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Numerical Simulation of Groundwater Flow in the Columbia Plateau Regional Aquifer System, Idaho, Oregon, and Washington By D. Matthew Ely, Erick R. Burns, David S. Morgan, and John J. Vaccaro

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All input and output available at linked website. Model developed following Supreme Court ruling on allocation of water among Colorado, Nebraska, and Kansas. Originally developed for 1918-2000 period and updated annually. Development team included representatives from each state and federal government. While the core model is MODFLOW, follow-on work has coupled it to agent-based and hydroeconomic models, and perhaps more that I am unaware of.

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A three-dimensional density dependent flow and transport model was developed for the Carbonate and Sandstone Aquifers in a 60,000 square-kilometre area of south-central Manitoba. Hydrogeological properties, such as transmissivity, and aquifer response data, were collected for both aquifers. Bayesian Updating was used to determine the heterogeneous transmissivity field of each aquifer. Other parameters were designated based on collected data or typical values from the literature. The resulting model was used to evaluate several water resources scenarios within the Province of Manitoba. The sustainability over 20 years with constant pumping rates was examined. Within both aquifers, hydraulic heads declined in some regions and on average a decline in head was predicted. Model simulations were also conducted to observe the effect of flooding as this is an issue of concern in southern Manitoba. A pseudo-flood was assumed to last for a period of one month. The model was run for a period of 50 years to observe the long-term effects. The solute transport results show a concentration increase in the region south of the City of Winnipeg after one-month, indicating a decline in water quality. Drought simulations were incorporated by reducing recharge rates to the aquifers. The hydraulic heads within the Carbonate Aquifer decline within the Interlake region with a maximum decline within the Sandilands region southeast of the City of Winnipeg. As might be expected, the effects of reduced recharge on the entire aquifer sequence are significant.

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Parsimonious groundwater modeling provides insight into hydrogeologic functioning of the Nubian Aquifer System (NAS), the world's largest non-renewable groundwater system (belonging to Chad, Egypt, Libya, and Sudan). Classical groundwater-resource issues exist (magnitude and lateral extent of drawdown near pumping centers) with joint international management questions regarding transboundary drawdown. Much of NAS is thick, containing a large volume of high-quality groundwater, but receives insignificant recharge, so water-resource availability is time-limited. Informative aquifer data are lacking regarding large-scale response, providing only local-scale information near pumps. Proxy data provide primary underpinning for understanding regional response: Holocene water-table decline from the previous pluvial period, after thousands of years, results in current oasis/sabkha locations where the water table still intersects the ground. Depletion is found to be controlled by two regional parameters, hydraulic diffusivity and vertical anisotropy of permeability. Secondary data that provide insight are drawdowns near pumps and isotope-groundwater ages (million-year-old groundwaters in Egypt). The resultant strong simply structured three-dimensional model representation captures the essence of NAS regional groundwater-flow behavior. Model forecasts inform resource management that transboundary drawdown will likely be minimal-a nonissue-whereas drawdown within pumping centers may become excessive, requiring alternative extraction schemes; correspondingly, significant water-table drawdown may occur in pumping centers co-located with oases, causing oasis loss and environmental impacts.

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Groundwater is the world's largest accessible source of fresh water. It plays a vital role in satisfying basic needs for drinking water, agriculture and industrial activities. During times of drought groundwater sustains baseflow to rivers and wetlands, thereby supporting ecosystems. Most global-scale hydrological models (GHMs) do not include a groundwater flow component, mainly due to lack of geohydrological data at the global scale. For the simulation of lateral flow and groundwater head dynamics, a realistic physical representation of the groundwater system is needed, especially for GHMs that run at finer resolutions. In this study we present a global-scale groundwater model (run at 6 0 resolution) using MODFLOW to construct an equilibrium water table at its natural state as the result of long-term climatic forcing. The used aquifer schematization and properties are based on available global data sets of lithology and transmissivities combined with the estimated thickness of an upper, unconfined aquifer. This model is forced with outputs from the land-surface PCRaster GlobalWater Balance (PCR-GLOBWB) model, specifically net recharge and surface water levels. A sensitivity analysis, in which the model was run with various parameter settings, showed that variation in saturated conductivity has the largest impact on the groundwater levels simulated. Validation with observed groundwater heads showed that groundwater heads are reasonably well simulated for many regions of the world, especially for sediment basins (R-2 = 0.95). The simulated regional-scale groundwater patterns and flow paths demonstrate the relevance of lateral groundwater flow in GHMs. Inter-basin groundwater flows can be a significant part of a basin's water budget and help to sustain river baseflows, especially during droughts. Also, water availability of larger aquifer systems can be positively affected by additional recharge from inter-basin groundwater flows.

NOTE: Model has global extent, bounding box is positioned over the Atlantic Ocean for visibility.

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The city of Santa Barbara, in cooperation with the U.S. Geological Survey (USGS) California Water Science Center, developed a three-dimensional density-dependent groundwater-flow and solute-transport model (the Santa Barbara Flow and Transport Model, or SBFTM), based on an existing groundwater-flow model, to simulate seawater intrusion into the Santa Barbara basin under various management strategies. In 2014, California adopted historic legislation to manage its groundwater: the Sustainable Groundwater Management Act (SGMA). Santa Barbara is interested in developing a better understanding of the sustainability of its groundwater supplies to avoid undesirable results: significant and unreasonable groundwater-level declines, reduction in groundwater storage, seawater intrusion, water-quality degradation, land subsidence, and surface-water depletion. The SBFTM uses the USGS code SEAWAT to simulate salinity transport and variable-density flow. The completed SBFTM was coupled with a management optimization tool, Borg, to develop five optimization scenarios that allow the decision makers to evaluate a range of optimal solutions given current water levels and chloride concentrations, and possible future climatic conditions. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20185059)

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Bari Doab on Pakistan side of the border, about 29,000 km2, is one of the most productive agricultural regions in the Sub-continent. The surge in population has increased the competition for available water resources. Ensuing to this, a number of irrigation-related issues have gained prominence. Effects of increasing climate aridity towards lower part of Bari Doab have emerged in the form of accelerated groundwater depletion. Lower Bari Doab Canal (LBDC) command, lying in the centre of Bari Doab, faces maximum spatial climate variability across its command area. This is the first model-based study of the long-term irrigation cost inequities due to successively increasing groundwater depletion towards the tail end. In the model, total water requirements of a grid cell are withdrawn from surface and/or sub-surface sources, based on rainfall and canal water availability. Groundwater pumping estimation is the most complex parameter; crop water deficit approach was adopted for the purpose. Due to excessive groundwater depletion, a tail-end farmer currently incurs 2.19 times higher irrigation costs as compared to the head-end counterpart. An additional depletion of 8-11 m is expected in the lower half of the command till 2031, in contrary to stable conditions in head end. As a result this irrigation cost anomaly is simulated to be further aggravating to 2.36 times in year 2031. Thus, irrigation systems with significant spatial climate variability need appropriate command scale conjunctive management of surface and groundwater by the concerned irrigation planning and management agencies. This would help in plummeting the exacerbating irrigation inequities by reducing waterlogging and groundwater depletion.

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In general, groundwater flow and transport models are being applied to investigate a wide variety of hydrogeological conditions besides to calculate the rate and direction of movement of groundwater through aquifers and confining units in the subsurface. Transport models estimate the concentration of a chemical in groundwater which requires the development of a calibrated groundwater flow model or, at a minimum, an accurate determination of the velocity and direction of groundwater flow that is based on field data. All the available hydrogeological, geophysical and water quality data in Musi basin, Hyderabad, India, were fed as input to the model to obtain the groundwater flow velocities and the interaction of surface water and groundwater and thereby seepage loss was estimated. This in turn paved the way to calculate the capacity of the storage treatment plants (STP) to be established at the inlets of six major lakes of the basin. The total dissolved solid was given as the pollutant load in the mass transport model, and through model simulation, its migration at present and futuristic scenarios was brought out by groundwater flow and mass transport modeling. The average groundwater velocity estimated through the flow model was 0.26 m/day. The capacities of STP of various lakes in the study area were estimated based on the lake seepage and evaporation loss. Based on the groundwater velocity and TDS as pollutant load in the lakes, the likely contamination from lakes at present and for the next 20 years was predicted.

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The application of groundwater resources in Punjab, Pakistan to meet the crop water requirements is increasing rapidly due to constrained surface water supplies. However, the abundant abstraction of groundwater has created serious negative concerns in terms of lowering water table. Thus the sustainability of regional groundwater resources depends upon its proficient management through groundwater modeling technique. Therefore, a research was accomplished to quantify the groundwater pumping and to identify the groundwater depletion areas using MODFLOW model. Three pumping scenarios were developed up to year 2030: such as Scenario-I (Maintaining the current pumping rate for the study period); Scenario-II (Increase in pumping rate according to the historical trend); and Scenario-III (Adjusted canal water supplies and groundwater patterns). The results of Scenario-I indicated that the groundwater level would decline up to 14m for the study period. Scenario-II results showed maximum decline of groundwater level, which would be 18m up to year 2030. The adjusted canal and groundwater supplies among upper and middle part of the study area in Scenario-III, which will recover the groundwater by 2-3m in the middle part of the study area, gave a good management strategy. So, in lower and middle part of study area, groundwater should be artificially recharged and more canal should be supplied water to avoid depletion.

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The exponential increase in groundwater usage over the past few decades in the Punjab province in Pakistan is responsible for the significant groundwater table decline in many parts of the province, leading to an urgent need for policy measures to better manage groundwater use. A better understanding of the underground water balance is necessary for drafting informed groundwater management plans. With limited data, this study develops the first physically-based groundwater model for the entire Punjab province. Using the calibrated provincewide model, simulations are performed to evaluate groundwater dynamics in the future under different scenarios. These scenarios comprise controls on groundwater pumping, canal infrastructure improvements, and precipitation changes. The impacts of these scenarios are highlighted with the mapping of changes in water table, pumping cost, and waterlogged area. The results show that changes in both groundwater abstraction and seepage from the canal system into the aquifer significantly impact groundwater heads, whereas the effect of changing precipitation is negligible. Under status quo conditions, the average provincewide pumping cost is projected to increase by 270% in 23years. The findings emphasize the heterogeneity in groundwater conditions across Punjab and highlight the need for region-specific management of groundwater resources. (C) 2016 American Society of Civil Engineers.

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A 3-D finite element model (Feflow) has been used for regional groundwater flow modelling of Upper Chaj Doab in Indus Basin, Pakistan. The thematic layers of soils, landuse, hydrology, infrastructure and climate were developed using Geographic Information System (GIS). The numerical groundwater flow model is developed to configure the groundwater equipotential surface, hydraulic head gradient and estimation of the groundwater budget of the aquifer. Integration of GIS with groundwater modelling and satellite remote sensing capabilities has provided an efficient way of analysing and monitoring groundwater status and its associated land conditions. The Arcview GIS software is used as additive tool to develop supportive data for numerical groundwater modelling, integration and presentation of image processing and modelling results. The groundwater behaviour of the regional model shows a gradual decline in watertable from year 1999 onward. The persistent dry condition and high withdrawal rates play an influential role in lowering down the groundwater levels. Different scenarios were developed to study the impact of extreme climatic conditions (drought/flood) and variable groundwater abstraction on the regional groundwater system. The results of the study provide useful information regarding the behaviour of aquifer in order to organize management schemes on local and regional basis to monitor future groundwater development in the area.

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Groundwater is a priceless resource in Alberta and therefore, estimating groundwater are crucial to identifying and promoting holistic and integrated management of groundwater-surface water. However, it is a challenge to simulate groundwater storage due to the current rudimentary representation of two-way groundwater-surface water exchange in current hydrologic models, such as Soil and Water Assessment Tool (SWAT), which, in turn, limits our ability to predict land-atmosphere processes and groundwater storage. In this study, we modified the SWAT model to improve module of evapotranspiration in two-way groundwater-surface water exchange. The modified SWAT was calibrated and validated against the groundwater table height and evapotranspiration from 2008 to 2011 period at two location (Lethbridge and Barons) Alberta, Canada. The results showed that the modified SWAT model predicts the groundwater table height very well at both locations. The modified model predicted the daily groundwater table height with R-2 values of 0.86 and 0.89 in the calibration period (2008-2009), 0.81 and 0.83 for the validation period (2010-2011) at Lethbridge and Barons, respectively. The Nash-Sutcliffe model efficiency (NSE) for daily groundwater table height was 0.69 and 0.71 during calibration periods (2008-2009) while the model gives lower values of NSE 0.65 and 0.67 for validation periods (2010-2011) at Lethbridge and Barons, respectively. Similarly, the model estimates evapotranspiration well with correlation coefficient (R-2) of 0.77 during the calibration period and 0.81 for validation period. Our result showed that the modified SWAT model did improve estimates to dynamic groundwater table heights.

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As part of the Quebec PACES III provincial groundwater resources assessment programme (Programme d'acquisition des connaissances en eaux souterraines), a regional-scale two-dimensional numerical groundwater model was developed in the Chaudiere-Appalaches region, Quebec, Canada. The model considers groundwater flow, transport of groundwater age and the influence of a fault on the flow system and its implications for groundwater quality. By including deep and shallow flow systems, the study helps fill a knowledge gap with respect to intermediate flow systems and the role they would play during potential energy resource development including shale gas exploitation from the Utica Shale. Physical and chemical hydrogeological data, including an analysis of C-14 in dissolved inorganic carbon in sampled groundwater, supported a regional conceptual flow model forming the basis for numerical simulations. The numerical model is first calibrated to regional piezometry through a semi-automated workflow using the inverse model PEST. Although some evidence for deeper regional flow exists, the area appears to be dominated by local flow systems on maximum length scales of about 5 km, with significant flow through the top 40 to 60 m of the fractured sedimentary rock aquifer. This regional-scale flow model is also supported by the local hydrogeochemical signatures. Simulated mean groundwater ages show young shallow water of <100 years with rapid increases in age with depth suggesting diffusion-controlled age evolution. Groundwater age is likely being perturbed in the vicinity of the Jacques Cartier River fault, which can act as both a barrier and a preferential pathway, provided permeability contrasts with the surrounding rock are at least two orders of magnitude.

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Since the 1970's the Ged Deeble (GD) basin is exploited to supply water to the town of Hargeisa (Somaliland, East Africa, 350,000 inhabitants). The goal of this work is to improve the comprehension of the recharge mechanisms, by the simulation of groundwater flow, in order to assess the sustainability of present-day and future exploitation schemes that aim to satisfy the water demand of the city. For this goal, the exploration activities performed in the past were used to reconstruct the geological framework, the basin shape and the mechanisms of recharge and to define the conceptual model. The mathematical model YAGMod, that simulates groundwater steady flow in presence of head-dependent sources and boundary conditions, was applied to quantify the terms of the groundwater balance. Different management scenarios, accompanied by a sensitivity analysis, have been examined to verify if the future water demand of the city could be satisfied and to provide some indications about the land use planning and the management of water resources.

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Many studies underline the importance of groundwater assessment at the larger, i.e. global, scale. The groundwater models used for these assessments are dedicated to the global scale and therefore not often applied for studies in smaller areas, e.g. catchments, because of their simplifying assumptions. In New Zealand, advanced numerical groundwater flow models have been applied in several catchments. However, that application is piecemeal: only for a limited amount of aquifers and through a variety of groundwater model suites, formats, and developers. Additionally, there are large areas where groundwater models and data are sparse. Hence, an inter-catchment, inter-regional, or nationwide overview of important groundwater information, such as the water table, does not exist. The investment needed to adequately cover New Zealand with high-resolution groundwater models in a consistent approach would be significant and is therefore not considered possible at this stage. This study proposes a solution that obtains a nationwide overview of groundwater that bridges the gap between the (too-) expensive advanced local models and the (too) simple global-scale models. We apply an existing, global-scale, groundwater flow model and improve it by feeding in national input data of New Zealand terrain, geology, and recharge, and by slight adjustment of model parametrisation and model testing. The resulting nationwide maps of hydraulic head and water table depths show that the model points out the main alluvial aquifers with fine spatial detail (200m grid resolution). The national input data and finer spatial detail result in better and more realistic variations of water table depth than the original, global-scale, model outputs. In two regional case studies in New Zealand, the hydraulic head shows excellent correlation with the available groundwater level data. Sensitivity and other analyses of our nationwide water tables show that the model is mostly driven by recharge, model resolution, and elevation (gravity), and impeded by the geology (permeability). The use of this first dedicated New Zealand-wide model can aid in provision of water table estimates in data-sparse regions. The national model can also be used to solve inconsistency of models in areas of trans-boundary aquifers, i.e. aquifers that cover more than one region in New Zealand. Comparison of the models, i.e. the national application (National Water Table model: NWT) with the global model (Equilibrium Water Table model: EWT), shows that most improvement is achieved by feeding in better and higher-resolution input data. The NWT model still has a bias towards shallow water tables (but less than the EWT model because of the finer model resolution), which could only be solved by feeding in a very high resolution terrain model that incorporates drainage features. Although this is a model shortcoming, it can also be viewed as a valuable indicator of the pre-human water table, i.e. before 90% of wetlands were drained for agriculture since European settlement in New Zealand. Calibration to ground-observed water level improves model results but can of course only work where there are such data available. Future research should therefore focus on both model improvements and more data-driven, improved estimation of hydraulic conductivity, recharge, and the digital elevation model. We further surmise that the findings of this study, i.e. successful application of a global-scale model at smaller scales, will lead to subsequent improvement of the global-scale model equations.

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To predict the movement of an existing creeping landslide, monitoring and analysis of hydrological parameters are crucial. This paper analyses the hydrological parameters of an existing creeping landslide site in western Japan. The groundwater flow and resulting fluctuation in pore water pressure at the slip layer of a sliding block was simulated using a groundwater flow model. A quasi-three-dimensional factor of safety of the block was obtained by combining the groundwater model with slope stability analysis methods. The results show that for prediction purposes at a creeping landslide site the time series analysis using long-term data is of limited use, because the fluctuations of ground surface movement and hydrological parameters are not completely synchronized when the factor of safety of the slope soil is in the creep movement range. The ground surface movement rate dropped after each episode of relatively big movement, even when the hydrological parameters were constant. The factor of safety of the sliding block was more influenced by groundwater recharge from the hills than by rainfall. Pore water pressure fluctuation obtained from groundwater flow model resulting from specific rainfall events indicated better relations between fluctuations in pore water pressure 3 and ground surface movement.

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Since 1900, Semarang City has been meeting its industrial water needs by pumping groundwater through its underlying aquifers. The trend toward exploiting groundwater resources has driven the number of deep wells and their production capacity to increase, and therefore leads to the water table to drop from time to time, which has been marked as one of the primary causes of land subsidence there. The main aim of the current study was to numerically model the temporal and spatial evolution of groundwater table under excess abstraction so that a groundwater management strategy can be accordingly drawn up for ensuing the sustainability of groundwater resources in the future. A series of numerical simulations were carried out to take into account hydrogeological data, artificial and natural discharges of deep wells, and boundary effects in Semarang City. The groundwater modeling is calibrated under two flow conditions of the steady state from 1970 to 1990 and the transient state from 1990 to 2005 for six observation wells distributed in Semarang City. Four scenarios that reflect potential management strategies were developed, and then their effectiveness was systematically investigated. The results of our study indicate that the implementation of proper groundwater control management and measure is able to restore the groundwater level to rise back in Semarang City, and in turn achieve the sustainability of groundwater resources.

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Location: Jakarta, Indonesia; Bachelor's Thesis focussing on sensitivity analysis.

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A methodology is proposed to define indices for quantifying risks under the threat of reducing in groundwater levels, the existence of saltwater intrusion (SWI), and an increasing nitrate contamination load in submarine groundwater discharge (SGD). The proposed methodology considers coastal regions under geological heterogeneity and it is tested on a groundwater system in Nassau County of Long Island, New York (USA). The numerical model is constructed with the SEAWAT code. The parameter uncertainty of this model is evaluated by coupling the Latin hypercube sampling method (as a sampling algorithm) and Monte Carlo simulation to consider the uncertainty in both hydraulic conductivity and recharge rate. The indices are presented in spatial maps that classify areas of risk to potential threats. The results show that two of the water districts have a high risk under conditions of decreasing groundwater level. Salinity occurs in the southern and southwestern parts of the Nassau County aquifer and a considerable area of high risk of SWI is identified. Furthermore, the average SGD rate with the associated fluxes of nitrate is estimated as 81.4 million m(3)/year (average 0.8 tons of nitrate through SGD per year), which can adversely affect the quality of life in the local coastal ecosystems. The framework developed in this study could help the water district managers to identify high-risk areas for short-term and long-term planning and is applicable to other coastal settings.

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A three-dimensional variable-density finite element model was developed to study the combined effects of overabstraction and seawater intrusion in the Pingtung Plain coastal aquifer system in Taiwan. The model was generated in different layers to represent the three aquifers and two aquitards. Twenty-five multilayer pumping wells were assigned to abstract the groundwater, in addition to 95 observation wells to monitor the groundwater level. The analysis was carried out for a period of 8 years (2008-2015 inclusive). Hydraulic head, soil permeability, and precipitation were assigned as input data together with the pumping records in different layers of the aquifer. The developed numerical model was calibrated against the observed head archives and the calibrated model was used to predict the inland encroachment of seawater in different layers of the aquifer. The effects of pumping rate, sea-level rise, and relocation of wells on seawater intrusion were examined. The results show that all layers of the aquifer system are affected by seawater intrusion; however, the lengths of inland encroachment in the top and bottom aquifers are greater compared with the middle layer. This is the first large-scale finite-element model of the Pingtung Plain, which can be used by decision-makers for sustainable management of groundwater resources and cognizance of seawater intrusion in coastal aquifers.

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The initial objectives of the efforts portrayed in this report were to (a) integrate all available groundwater data available in the Lake Chad Basin in an updated database; (b) develop an updated and integrative conceptual groundwater model of the Lake Chad Basin, including all old and new information and reflecting the best current understanding, and (c) develop the equivalent numerical groundwater model of the Lake Chad Basin, with emphasis on two focus areas: the Komadougu-Yobe and Chari-Logone river basins, given their relevance for groundwater recharge and use. Even though the overall conceptual model and the numerical model need to be further improved, the basin-wide perspective presented in this work, integrating multiple sources of available data, provides a foundation to better understand and quantify basin-wide hydrogeological dynamics. This enables future efforts to assess potential impacts of future investments and climate futures.

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The Nile Delta Aquifer (NDA) is threatened by salt water intrusion (SWI). This article demonstrates an approach for identifying critical salinity concentration zones using a three-dimensional (3D) variable-density groundwater flow model in the NDA. An innovative procedure is presented for the delineation of salinity concentration in 2010 by testing different simulation periods. The results confirm the presence of saline groundwater caused by SWI in the north of the NDA. In addition, certain regions in the east and southwest of the NDA show increased salinity concentration levels, possibly due to excessive groundwater extraction and dissolution of marine fractured limestone and shale that form the bedrock underlying the aquifer. The research shows that the NDA is still not in a state of dynamic equilibrium. The modeling instrument can be used for simulating future scenarios of SWI to provide a sustainable adaptation plan for groundwater resource.

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Coastal freshwater resources are commonly under high risk of being contaminated from seawater. The main processes that affect seawater intrusion are groundwater overexploitation, land use change, and climate change effects. In this context coastal lagoons represent the more sensitive environments prone to seawater intrusion. Numerical modelling is a useful tool to understand and predict seawater intrusion. In this study, a three-dimensional SEAWAT model is employed to simulate the seawater intrusion to coastal aquifers of Variconi Oasis (Italy). The present simulation was divided into a calibration and a validation model, then the model was used to predict the salinization trend up to 2050. Results show the role of the sea in salinizing the beach front, while the retrodunal environment is characterized by transitional environments. Future seawater intrusion scenarios considering only climate data showed no significative differences in respect to the actual situation. The same happens considering also a low sea level rise prediction. On the contrary, the worst scenario (high sea level rise prediction), depicts a quite different situation, with a saline intrusion in the Variconi oasis that will severely affect the fragile transitional ecosystem. This modelling framework can be used to quantify the effects of climate changes in similar coastal environments.

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Regional three-dimensional groundwater-flow and saltwater transport models were built to analyse saltwater intrusion in the Great Maputo area, southern Mozambique. Increased water demand has led to many private groundwater abstractions, as the local public water supply network has already reached maximum capacity. Pushing for new strategies to tackle the water-supply shortages exposes the aquifer system to saltwater intrusion from entrapped fossil saline groundwater and seawater. Previous attempts at modelling have been frustrated by data limitations. This study compiled all the available data to build the models, which were subsequently calibrated with observed heads, discharges and salt concentrations. The transport models were used to test hypotheses of potential sources of saltwater resulting in the current salinity distribution. Furthermore, scenarios were simulated to assess the impacts of sea-level rise and projected groundwater abstractions. Results show that saline groundwater is widely distributed in the aquifer's western sector, where it is a limiting factor for groundwater development, and seawater intrusion is a risk along the coastline. Newly constructed wells (46) along the Infulene River can be operated with some impacts of saltwater upconing and must be closely monitored. Although current groundwater abstractions (60,340 m(3)/day) are still small compared with groundwater recharge (980,823 m(3)/day), larger volumes of abstraction are feasible only when using a high number of production wells further away from the city with relatively low yields to avoid saltwater upconing. Capture of fresh groundwater upstream of discharge areas by wells for water supply is possible while maintaining groundwater discharges for groundwater dependent ecosystems.

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Since 1980s, seawater intrusion in coastal aquifers caused by groundwater over-abstraction has led to extensive deterioration in groundwater quality and quantity and has been fazing local residents in Zhoushuizi district of the metropolitan Dalian City in northern China. In this study, a three-dimensional (3D) density-dependent numerical model was constructed to simulate the seawater intrusion process in heterogeneous coastal aquifers in Zhoushuizi district of the metropolitan Dalian City. Considering that the groundwater flow in karst aquifers in northern China is relatively uniform, approximately following Darcy's law, the fracture-karst aquifer in Zhoushuizi district of Dalian City was simplified as an equivalent porous medium. To further identify the hydrogeological parameters of the aquifers in the study area, the model was calibrated and validated using the observation heads and concentrations. Based on the current groundwater abstraction conditions of the study area, the calibrated and validated model was then applied to predict the dynamics and trend of seawater intrusion for the following 30 years from 2010 to 2040 under different rainfall scenarios. The overall extent of seawater intrusion in the future would be even more severe under different prediction scenarios. This 3D seawater intrusion model provides the theoretical basis for implementing a reasonable allocation of groundwater resource, which may significantly affect the sustainability of water resources.

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A re-calibration of the Republican River Compact Administration (RRCA) Groundwater Model only for the northwest Kansas portion of the model. The report misses some essential information (blank answers above), but can be complemented by the original RRCA Groundwater Model's reports/data.

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The city of Rapid City and other water users in the Rapid City area obtain water supplies from the Minnelusa and Madison aquifers, which are contained in the Minnelusa and Madison hydrogeologic units. A numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units in the Rapid City area was developed to synthesize estimates of water-budget components and hydraulic properties, and to provide a tool to analyze the effect of additional stress on water-level altitudes within the aquifers and on discharge to springs. This report, prepared in cooperation with the city of Rapid City, documents a numerical groundwater-flow model of the Minnelusa and Madison hydrogeologic units for the 1,000-square-mile study area that includes Rapid City and the surrounding area. Water-table conditions generally exist in outcrop areas of the Minnelusa and Madison hydrogeologic units, which form generally concentric rings that surround the Precambrian core of the uplifted Black Hills. Confined conditions exist east of the water-table areas in the study area. The Minnelusa hydrogeologic unit is 375 to 800 feet (ft) thick in the study area with the more permeable upper part containing predominantly sandstone and the less permeable lower part containing more shale and limestone than the upper part. Shale units in the lower part generally impede flow between the Minnelusa hydrogeologic unit and the underlying Madison hydrogeologic unit; however, fracturing and weathering may result in hydraulic connections in some areas. The Madison hydrogeologic unit is composed of limestone and dolomite that is about 250 to 610 ft thick in the study area, and the upper part contains substantial secondary permeability from solution openings and fractures. Recharge to the Minnelusa and Madison hydrogeologic units is from streamflow loss where streams cross the outcrop and from infiltration of precipitation on the outcrops (areal recharge). MODFLOW-2000, a finite-difference groundwater-flow model, was used to simulate flow in the Minnelusa and Madison hydrogeologic units with five layers. Layer 1 represented the fractured sandstone layers in the upper 250 ft of the Minnelusa hydrogeologic unit, and layer 2 represented the lower part of the Minnelusa hydrogeologic unit. Layer 3 represented the upper 150 ft of the Madison hydrogeologic unit, and layer 4 represented the less permeable lower part. Layer 5 represented an approximation of the underlying Deadwood aquifer to simulate upward flow to the Madison hydrogeologic unit. The finite-difference grid, oriented 23 degrees counterclockwise, included 221 rows and 169 columns with a square cell size of 492.1 ft in the detailed study area that surrounded Rapid City. The northern and southern boundaries for layers 1-4 were represented as no-flow boundaries, and the boundary on the east was represented with head-dependent flow cells. Streamflow recharge was represented with specified-flow cells, and areal recharge to layers 1-4 was represented with a specified-flux boundary. Calibration of the model was accomplished by two simulations: (1) steady-state simulation of average conditions for water years 1988-97 and (2) transient simulations of water years 1988-97 divided into twenty 6-month stress periods. Flow-system components represented in the model include recharge, discharge, and hydraulic properties. The steady-state streamflow recharge rate was 42.2 cubic feet per second (ft3/s), and transient streamflow recharge rates ranged from 14.1 to 102.2 ft3/s. The steady-state areal recharge rate was 20.9 ft3/s, and transient areal recharge rates ranged from 1.1 to 98.4 ft3/s. The upward flow rate from the Deadwood aquifer to the Madison hydrogeologic unit was 6.3 ft3/s. Discharge included springflow, water use, flow to overlying units, and regional outflow. The estimated steady-state springflow of 32.8 ft3/s from seven springs was similar to the simulated springflow of 31.6 ft3/s, which included 20.5 ft3

ABSTRACT:

Ground-water levels have been declining during the last few decades in the Ogallala-High Plains aquifer (HPA) in western Kansas, including within Southwest Kansas Groundwater Management District No. 3 (GMD3). The water-level declines have decreased ground-water discharge to the Arkansas and Cimarron rivers, thereby causing decreasing streamflow. One of the Kansas Water Plan (KWP) objectives is to "Reduce water-level declines rates within the Ogallala aquifer and implement enhanced water management in targeted areas." An associated goal of the KWP is to "Conserve and extend the life of the HPA." As a part of planning and management activities, the Kansas Water Office (under a cooperative agreement with the U.S. Bureau of Reclamation) and GMD3 contracted with the Kansas Geological Survey (KGS) to develop a computer model of the HPA in the GMD3 area to further characterize the hydrologic system and water availability. The model will provide more information on water in storage and allow projection of likely aquifer responses to possible future conditions and management scenarios (KWP, Upper Arkansas River Basin High Priority Issue, Management of the HPA). The KGS constructed a numerical model for a rectangular area of 100 by 150 miles that enclosed GMD3 and extended approximately 6 miles to the north, east, south (into Oklahoma), and west (into Colorado) of the GMD3 boundaries. The active cells included the paleovalley of the Arkansas River in Hamilton and western Kearny counties. The KGS model utilizes MODFLOW, a widely used software program for modeling ground-water flow and stream- aquifer interactions developed by the U.S. Geological Survey. The KWO formed a Technical Advisory Committee to oversee the project, which included staff of the KWO, GMD3, KDA- DWR, and a consulting firm retained by KDA-DWR to provide technical review. The main focus of the project was the development of a calibrated transient model that simulated ground-water flow and stream-aquifer interactions during the period 1947-2007. Predevelopment conditions were simulated for 1944-1946. The model included 12,083 active model cells (each a mile square), involved one layer, and simulated ground-water flow in the HPA and associated alluvial aquifers. Six recharge zones were used and the types of recharge included that from precipitation, enhancement of precipitation recharge in irrigated land, and return recharge below fields irrigated with ground-water and river water diverted from the Arkansas River. The precipitation applied to each cell varied depending on the distribution for each year across the model area. Ground-water pumpage from the HPA for Kansas during 1990-2007 was based on reported water-use records, and for earlier years was estimated from regression equations based on a de-trended ratio of water use/authorized quantity versus precipitation and the Palmer drought severity index for 1990-2007. Similar approaches were applied to estimating pumpage in the Colorado and Oklahoma portions of the model, although the procedures varied because the data and data access for pumping records are not as readily available as those for Kansas. The pumpage rate from the HPA increased from 78,000 acre-ft/yr for predevelopment to a maximum of 2,708,000 acre-ft/yr in 1991 and was 1,844,000 acre-ft/yr for 2007 in the modeled area. The percentage of irrigation return recharge was calculated for each year in Kansas counties based on data for changes in irrigation type and applied to adjacent counties in Colorado and Oklahoma. Results from the calibrated model indicated that the long-term recharge from areal precipitation averaged over the model area was 0.41 in/yr during 1946-2007. Stream-aquifer interactions were simulated for the Arkansas and Cimarron rivers and Crooked Creek. Hydraulic conductivity (K) and specific yield (Sy) were estimated using lithologic data from about 15,000 well logs examined by the KGS PST+ (practical saturated thickness) program. In order to account for the impact of declining water levels on the calculation of K and Sy during the transient period, the calibrated model was broken into six step models: 1) predevelopment, 2) predevelopment to 1966, 3) 1967 to 1976, 4) 1977 to 1986, 5) 1987 to 1996 and 6) 1997 to 2007. In each step model, K and Sy were dynamically updated using the observed water levels for the corresponding time period. During model calibration, the K and Sy values were adjusted by matching streamflows and observed water levels during each step to simulated values. A recharge function with different parameters for each of the six recharge zones was also incorporated into the calibration. The parameter estimation program PEST was employed to optimize parameters during the calibration process. The model indicates that ground-water pumping has caused substantial decreases in aquifer storage. The storage decline rate started to increase in the 1950s, accelerated in the 1960s to mid-1970s, and then approximately leveled from the late 1970s to 2007, although it varied substantially each year depending on pumping. The accumulated decline in ground-water storage simulated for the entire model area for 1947-2007 is 66,409,000 acre-ft, which comprises 29.3% of the simulated predevelopment storage. The storage decreases have been accompanied by a decrease in streamflow out of the model. Water-level declines in the HPA have resulted in the "capture" of ground water that otherwise would have discharged to streams; without this capture, the aquifer storage loss would have been approximately 12% greater than simulated. The total storage volumes simulated for the HPA only within the GMD3 area for predevelopment and the end of 2007 are 193,454,000 and 133,622,000, respectively, giving a storage decline of 59,832,000 acre-ft, which is 30.9% of the predevelopment value. The total storage volumes computed for the GMD3 area from measured water levels are 191,216,000 and 133,726,000 acre-ft for predevelopment and 2007, respectively. These values give a storage decrease of 57,490,000 acre-ft, which is 30.1% of the predevelopment volume. The storage volumes from the model and estimated from observations for the GMD3 area differ by only 1.2% and 0.1% for predevelopment and 2007 conditions. The average water-level decline simulated for all the model cells within the GMD3 area is 69.89 ft in comparison with 67.01 ft for the difference between contoured water-level surfaces based on observations in the predevelopment period to 2007. The calibrated model will be used to simulate ground-water flow and stream-aquifer interactions for future conditions involving continuation and changes in pumping, and different climatic conditions as selected by the KWO and GMD3. A separate report that presents and discusses the results of these scenarios will be prepared.

ABSTRACT:

The study described in this report, initiated by the U.S. Geological Survey in 2014, was designed to evaluate fresh groundwater resources within the Ozark Plateaus, central United States, as an area within a broader national assessment of groundwater availability. The goals of the Ozark study were to evaluate historical effects of human activities on water levels and groundwater availability, quantify groundwater resources now and under probable future pumping and climate conditions, and evaluate existing monitoring networks for their value in making better predictions of future groundwater resources. Previous studies include simulation of local-scale groundwater flow under varying temporal scales, or simulation of the regional system under steady-state conditions. While these studies are useful, particularly for the problem for which they were designed, there is a need to look at the larger regional system under transient conditions to fully evaluate the water resource over time. This study focused on multiple spatial and temporal scales to examine changes in groundwater pumping, storage, and water-level declines. The regional scale provides a broad view of the sources and demands on the system with time. The study area covers approximately 68,000 square miles in the central United States in parts of Missouri, Arkansas, Kansas, and Oklahoma and encompasses the Ozark Plateaus Physiographic Province (Ozark Plateaus), including the Salem Plateau, Springfield Plateau, and Boston Mountains. Groundwater is withdrawn from the Ozark Plateaus aquifer system (Ozark system) for public supply and for domestic, agriculture (including irrigation and aquaculture), livestock, and non-agricultural use (including industrial, thermoelectric power generation, mining, and commercial). The Ozark system provides an important drinking-water supply for people living in the Ozark Plateaus because public supply and domestic use combined constitute the largest groundwater use. Precipitation is the ultimate source of freshwater to the Ozark system; most rainfall occurs during April, May, and June, and precipitation increases generally from north to south across the study area. Groundwater use currently accounts for only 10 percent of the total water use in the areas overlying the Ozark system, but provides a critical drinking-water resource because public supply and domestic groundwater withdrawals are largely from groundwater resources. The 380 million gallons per day of groundwater withdrawn from the Ozark system in 2010 accounts for approximately 2 percent of recharge. Although groundwater use represents a small component of the hydrologic budget, because of low storage in aquifer units, cones of depression with steep water-level gradients can develop quickly around pumping centers. The amount of water entering and leaving the aquifer system from 1900 to about 1965 was relatively constant at a rate of about 13 billion gallons per day (Bgal/d). Much of this inflow of water is discharged through streams in the system to balance the hydrologic budget. Changes in storage over time (from outflows to inflows) reflect the large variability in recharge: if recharge decreases, water levels will decrease, resulting in less groundwater discharge to streams and more water released from aquifer storage. Conversely, when recharge increases, water levels increase, more groundwater discharges to streams, and aquifer storage is replenished. Although pumping generally increased from 1900 to 2016, it does not appear to correlate with the change in storage over the same time period. Regionally, simulated change in groundwater storage corresponds with changes in recharge, more so than with increases in pumping. Average recharge was 11.6 Bgal/d for the period 1900 to 2016. Recharge was generally above average from predevelopment to 1965, followed by a period of below-average recharge from 1965 to about 1980. Recharge remained consistently above average from 1980 to about 1988, after which there was a period of average or below-average recharge, reflected by a decline through the mid-2000s. The implications and potential effects of increased pumping and long-term climate change on the Ozark Plateaus hydrologic system and groundwater availability are a concern for communities and resource managers in the area. Pumping varies from year to year, but is generally expected to moderately increase with population, industrial, and agricultural needs. Most climate models predict warmer minimum and maximum air temperatures by midcentury in the Ozark Plateaus area, especially from midspring through early fall. Three scenarios were developed to simulate possible future conditions from 2016 to 2060 and assess the potential effects on the hydrologic system and availability of water resources. For each scenario, changes in water levels and hydrologic budget components were evaluated from predevelopment (1900) to present (2016) and 45 years into the future (2060). The baseline scenario represents an extension of the average (1996 to 2016) seasonal pumping and recharge values. The pumping scenario is an extension of the average (1996 to 2016) seasonal recharge values with increases in pumping following the historical trend for the period 2016-2060 of up to 120 percent of the 1996 to 2016 average seasonal pumping values. The general circulation model (GCM) scenario is an extension of the average (1996 to 2016) seasonal pumping values and variable recharge based on seasonal averages of soil water storage from a water-balance model using temperature and precipitation from multiple GCMs. The general patterns of water-level decline are similar for each scenario. The areas of water-level decline in southwest Missouri and northeast Oklahoma are only marginally different by 2060 from those of 2009. In one area south of Springfield, Mo., water-level declines are less in the baseline and GCM scenarios than in 2009. This may be the result of a transition from groundwater use to surface-water supplies for a larger percentage of the demand in the area. For all three scenarios, forecasted pumping, recharge, and aquifer properties play an important role in determining the uncertainty of water-level forecasts at 94 real-time observation wells. Simulated aquifer properties in the productive middle and lower Ozark aquifers and the St. Francois confining unit of the Ozark system contribute most to predictive uncertainty in water levels at approximately 35 percent of the real-time observation wells. Out of the 94 real-time observation wells, 82 are developed in the lower Ozark aquifer.

ABSTRACT:

The city of Aberdeen, in northeastern South Dakota, requires an expanded and sustainable supply of water to meet current and future demands. Conceptual and numerical models of the glacial aquifer system in the area north of Aberdeen were developed by the U.S. Geological Survey in cooperation with the City of Aberdeen in 2012. The U.S. Geological Survey, in cooperation with the City of Aberdeen, completed a study to revise the original numerical groundwater-flow model using data through water year (WY) 2015 to aid the City of Aberdeen in their development of plans and strategies for a sustainable water supply and to increase understanding of the glacial aquifer system and groundwater-flow system near Aberdeen. The original model was revised to improve the fit between model-simulated values and observed (measured or estimated) data, provide greater insight into surface-water interactions, and improve the usefulness of the model for water-supply planning. The revised groundwater-flow model (hereafter referred to as the revised model) presented in this report supersedes the original model. The purpose of this report is to describe a revised groundwater-flow model including data collection, model calibration, and model results for the glacial aquifer system including the Elm, Middle James, and Deep James aquifers north of Aberdeen, South Dakota, using updated hydrologic data through WY 2015. The original numerical model was revised in several ways. The model was modified by adding four new layers, which included a surficial layer, two intervening confining layers, and a shale bedrock layer. The revised model provides an improved understanding of the groundwater-flow system in comparison to the original model. The principal aquifers of the model area include portions of the Elm, Middle James, and Deep James aquifers. The lithologic information used to define and describe the aquifers in the model area was unaltered; however, aquifer properties and boundary conditions were reviewed and updated using geological information reported by the South Dakota Department of Environmental and Natural Resources and information obtained from geophysical investigations for this study. The horizontal extent of the Elm, Middle James, and Deep James aquifers was unaltered from the original model. The thickness of the Deep James aquifer was modified based on interpretations from the geophysical investigations. In general, groundwater in the Elm aquifer flowed from northwest to southeast and locally towards rivers and streams. Similarly, in the Middle James and Deep James aquifers, groundwater also typically flowed southeast. The revisions made to the original model include use of the following MODFLOW stress packages: Recharge, Evapotranspiration, Time-Variant Specified Head, Wells, Drains, and Stream Flow Routing, all of which were updated from the original model except for the Stream Flow Routing Package, which replaced the River Package used in the original model. Model calibration is the process of estimating model parameters to minimize the differences, or residuals, between observed data and simulated values; therefore, Parameter ESTimation (PEST) software was used to optimize model input parameters by matching model-simulated values to observed data. Calibration parameters included horizontal hydraulic conductivity, vertical hydraulic conductivity, specific yield, specific storage, and vertical streambed conductance for stream and drain cells. Multipliers were used to calibrate the recharge and evapotranspiration stresses. Evapotranspiration extinction depth also was adjusted during model calibration. Comparisons to the original model are described to highlight the changes made in the revised model. In general, the revised model adequately simulates the natural system and compares favorably with observed hydrologic data. Simulated water levels were evaluated by comparing them to single water-level observations at selected well locations. The selected wells were the same wells used in the original model. The coefficient of determination value between simulated and observed water levels for the revised model was 0.89 and included simulated and observed values from October 1, 1974 (WY 1975), through September 30, 2015 (WY 2015). The coefficient of determination value for the original model was 0.94 and included simulated and observed values from October 1, 1974, through September 30, 2009. The difference may indicate that the original model could have been overfit to hydraulic head observations because base flow was not simulated. The additional data used in the revised model included some climatically wetter, more extreme periods, such as 2011, in which annual precipitation was 30.9 inches. Average annual precipitation for the original model timeframe, which included data from WYs 1975-2009, was 20.26 inches. Additional precipitation data for WYs 2010-15, included in the revised model timeframe, resulted in an average annual precipitation for WYs 1975-2015 in the model area of 20.6 inches. The larger variability in climate data coupled with the additional water-level data could explain the lower coefficient of determination for water levels in the revised model. The revised model was used to calculate various groundwater-budget components for steady-state and transient conditions for WYs 1975-2015. The time-variant specified-head cells in the revised model had the largest change when compared to the original steady-state model for inflows and outflows. Comparing the transient budget components between the original and the revised models indicated that inflow from recharge and time-variant specified-head cells had the greatest effect on groundwater inflows, and outflow from storage had the greatest effect on groundwater outflows. The simulated potentiometric contours from the revised model were compared with (1) the observed (interpreted) potentiometric surface (layer 2) and the hydraulic head values (layers 4 and 6) and (2) the simulated contours from the original model. The simulated hydraulic gradients and general direction of groundwater flow in the Elm aquifer in the revised model generally matched the observed potentiometric contours, the simulated potentiometric contours from the original model, and general flow directions interpreted to be perpendicular to the contours. Minor discrepancies between simulated potentiometric contours from the revised model and the observed potentiometric contours may be due to the lack of observed data in the model area. The revised model was designed to reduce the limitations of the original model. The revisions were validated by comparing the results of the original model with the revised model. A primary benefit of the revised model is the inclusion of the surficial deposits and the confining units as explicit layers in the model. The addition of the surficial layer was beneficial for three primary reasons: (1) more accurate representation of recharge from precipitation, (2) more accurate representation of groundwater evapotranspiration, and (3) more accurate representation of groundwater and surface-water interactions. The groundwater model is a numeric approximation of a complex physical hydrologic system, and the revised model data were interpolated in regions with sparse data. Additionally, model discretization included averaged and interpolated values for water use, withdrawal rates, and hydraulic conductivity. The revised model provides a useful estimate for hydraulic gradients, groundwater-flow directions, and aquifer response to groundwater withdrawals.

ABSTRACT:

The development of new, large-scale tools to evaluate water resources is critical to understanding the long-term sustainability of this resource under future land use, climate change, and population growth. In cold and humid regions it is imperative that such tools consider the hydrologic complexities associated with permafrost and groundwater-surface water (GW-SW) interactions, as these factors are recognized to have significant influence on the global water cycle. In this work we present a physics-based, three-dimensional, fully-integrated GW-SW model for Continental Canada constructed with the HydroGeoSphere simulation platform. The Canadian Continental Basin Model (CCBM) domain, which covers approximately 10.5 million km(2), is discretized using an unstructured control-volume finite element mesh that conforms to key river basin boundaries, lakes, and river networks. In order to construct the model, surficial geology maps were assembled, which were combined with near-surface information and bedrock geology into a seven-layer subsurface domain. For the large-scale demonstration, the model was used to simulate historic groundwater levels, surface water flow rates (R-2=0.85), and lake levels (R-2=0.99) across the domain, with results showing that these targets are well reproduced. To demonstrate the regional-scale utility, simulation results were used to perform a regional groundwater flow analysis for western Canada and a water balance analysis for the Laurentian Great Lakes (Superior, Michigan, Huron, Erie and Ontario). The outcome of this work demonstrates that large-scale fully-integrated hydrologic modeling is possible and can be employed to quantify components of a large-scale water balance that are otherwise difficult or impossible to obtain.

ABSTRACT:

The following paper describes the goals and some preliminary work in the Bani sustainability study, an ongoing project in Mali, West Africa. Rural communities in Mali are increasingly relying on hand-pumps, which tap groundwater resources, as a means of obtaining potable water. The long-term sustainable yield of groundwater resources is not known but can be evaluated in sustainability study. In 2005, a groundwater sustainability Study was established along the Bani River of Mali. The Bani study collected groundwater levels that were used in a conceptual groundwater flow model-the Bani model-to develop an understanding of current aquifer conditions and to make limited predictions of sustainability under various future scenarios. The Bani model showed the climatic parameters of recharge (derived from precipitation) and evapotranspiration to influence simulated groundwater levels and groundwater volume available, while increased pumping rates, due to population growth, showed little effect. When considered in the context of the actual Bani sustainability study area, the change in groundwater levels resulting from climatic parameters may have negative implications, especially during several consecutive years of decreased precipitation, such as drought, or if downward trends anticipated for precipitation continue.

ABSTRACT:

The Annapolis-Cornwallis Valley Aquifer Study was a regional hydrogeological study focusing on major aquifer units of the most important agricultural area of Nova Scotia. The study area covered 2100 km2, and included sedimentary rocks of the Wolfville and Blomidon formations, as well as part of the North and South mountains bordering the valley. The surficial sediment cover is mainly composed of glacial tills, but sand and gravel units are also present in the eastern part of the valley. The main objectives of this project were to improve the general understanding of groundwater flow dynamics and to provide baseline information and tools for a regional groundwater resource assessment. The main bedrock aquifers of the Valley are located in the Wolfville and Blomidon formations, which are composed of lenticular bodies of sandstone, conglomerate, shale and siltstone in variable proportions. The aquifers are often confined and the flow is topographically-driven. Their hydraulic conductivities are in the range of 10-6-10-5 m/s. Good aquifers, though limited in extent, can also be found in the sand and gravel units, with hydraulic conductivities on the order of 10-4 m/s. Groundwater recharge was estimated to range between 115 and 224 mm/a over the entire study area. The vulnerability study showed that bedrock aquifers are typically less vulnerable than surficial aquifers, with the Wolfville Formation being the most vulnerable bedrock formation. Groundwater of the Valley is generally of good quality, although nitrate levels are of concern in several areas.

ABSTRACT:

Groundwater (GW) is the main source of domestic water supply in Ethiopia (85%), however, despite widespread acknowledgement of its potential for resource-based development and climate change adaptation, the sector is still quite under-investigated. This is mainly due to the scarcity of in situ data, which are essential to building robust impact models. To address this, we developed a fine-resolution (500 m) GW model using MODFLOW-NWT, focusing on the Gilgel-Abay Catchment located in the Upper Blue Nile basin, fed with daily distributed input forcings of recharge and streamflow simulated by the Coupled Routing and Excess Storage (CREST) hydrological model. The model was calibrated against instantaneous observation records of GW table for 38 historical wells, and validated at selected sites using time series data collected from the Citizen Science Initiative (PIRE CSI), and the Innovation Lab for Small Scale Irrigation (ILSSI) project. An RMSE of 14.4 m (1.8% of range) was achieved for calibration and same for validation was 18.21 m and 15.76 mat the PIRE CSI and ILSSI sites, respectively. The findings of this research indicate substantial physical GW resource availability in the Gilgel-Abay region. Moreover, we expect the model to have multiscale future applications. These include obtaining dynamically downscaled boundary conditions for a local-scale GW model, to be developed in the next phase of our research. Further, an upscaled version of this model to encompass the entire Tana Basin would be developed to simulate lake-aquifer interactions. Finally, the approach of this research combining different types of datasets (e.g., reanalysis products, satellite data, citizen science data, etc.) is adaptable to other global data-scarce regions. Moreover, the method overcomes specific challenges associated to in situ data scarcity, limited knowledge on GW resources availability in the area, interaction with complex boundary conditions, and sensitivity under meteorological boundary forcings.

ABSTRACT:

Tunisia relies extensively on coastal groundwater resources that are pumped at unsustainable rates to support irrigated agriculture, causing groundwater drawdown and water quality problems due to seawater intrusion. It is imperative for the country to regulate future groundwater allocations and implement conservation strategies based on robust hydrogeological assessments to alleviate the adverse impacts of groundwater depletion. We developed a 3D transient density-dependent groundwater model by coupling MODFLOW-2000 and MT3DMS to improve understanding of seawater intrusion into the Korba aquifer in Tunisia. Results indicate that groundwater overexploitation since 1965 induced 5.15 Mm(3)/year of seawater inflow while reducing submarine discharge into the sea by about 9.74 Mm(3)/year as compared to the steady state water budget in 1965. Projecting withdrawals from 2014 up to 2050 results in a slow but extensive groundwater table decline forming a cone of depression 15 m below sea level. The seawater wedge under this business-as-usual scenario is expected to reach 1.8 km from the shoreline, causing significant mixing of the TDS-rich seawater in the aquifer system. The cone of depression under a 25% increase in groundwater withdrawal drops to about 20 m below sea level while the saltwater front reaches 2.5 km inland. Countering the seawater intrusion problem requires reducing groundwater pumping by 17 Mm(3)/year to push back the saltwater front along the coastline by about 25% over a 43-year period. Application of the presented generic groundwater simulation framework guides developing management strategies to mitigate seawater intrusion in the Korba coastal aquifer and similar areas.

ABSTRACT:

Water management in the Netherlands applies to a dense network of surface waters for discharge, storage and distribution, serving highly valuable land-use. National and regional water authorities develop long-term plans for sustainable water use and safety under changing climate conditions. The decisions about investments on adaptive measures are based on analysis supported by the Netherlands Hydrological Instrument NHI based on the best available data and state-of-the-art technology and developed through collaboration between national research institutes. The NHI consists of various physical models at appropriate temporal and spatial scales for all parts of the water system. Intelligent connectors provide transfer between different scales and fast computation, by coupling model codes at a deep level in software. A workflow and version management system guarantees consistency in the data, software, computations and results. The NHI is freely available to hydrologists via an open web interface that enables exchange of all data and tools. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).

ABSTRACT:

The Guarani Aquifer System (GAS) is a strategic transboundary aquifer system shared by Brazil, Argentina, Paraguay and Uruguay. This article presents a groundwater flow model to assess the GAS system in terms of regional flow patterns, water balance and overall recharge. Despite the continental dimension of GAS, groundwater recharge is restricted to narrow outcrop zones. An important part is discharged into local watersheds, whereas a minor amount reaches the confined part. A three-dimensional finite element groundwater-flow model of the entire GAS system was constructed to obtain a better understanding of the prevailing flow dynamics and more reliable estimates of groundwater recharge. Our results show that recharge rates effectively contributing to the regional GAS water balance are only approximately 0.6 km(3)/year (about 4.9 mm/year). These rates are much smaller than previous estimates, including of deep recharge approximations commonly used for water resources management. Higher recharge rates were also not compatible with known(81)Kr groundwater age estimates, as well as with calculated residence times using a particle tracking algorithm.

ABSTRACT:

The poor management of the leachates generated at the solid waste final disposal site in El Carrasco, Bucaramanga, Colombia, has been worrying environmental authorities for some years because its risk of contamination for the soil and the water in the disposal and closed areas. Objective. To establish the migration route for the leachates generated in El Carrasco landfill, in Bucaramanga, and in the direct and indirect areas of influence of the disposal site, by means of the analysis and the interpretation of the data obtained by the use of geoelectric units. Materials and methods. IT tools were used, including geographic information systems, the Modelmouse software, 180 meters deep vertical electrical soundings with a mesh modeling model comprised of 45 lines and 35 columns -10x10m- and six layers that met the units identified in the direct disposal area by means of a stratigraphic profile. Results. The results of the modeling developed within the MODFLOW environment show an East-West flow in most of the layers. The same happens with the flow established by the load coming from the Santander mountain range, where the resistivity rates are very low. Conclusion. Low resistivity zones associated, generated by the leachates, and fully saturated zones that were poorly managed in the disposal site, were identified for the area studied, by means of methodologies that combine geophysics, geology, hydrogeology and geochemistry.

ABSTRACT:

The U.S. Geological Survey, in cooperation with the Lewis and Clark, Lower Elkhorn, Lower Loup, Lower Platte North, Lower Niobrara, Middle Niobrara, Upper Elkhorn, and the Upper Loup Natural Resources Districts, designed a study to refine the spatial and temporal discretization of a previously modeled area. This updated study focused on a 30,000-square-mile area of the High Plains aquifer and constructed regional groundwater-flow models to evaluate the effects of groundwater withdrawal on stream base flow in the Elkhorn and Loup River Basins, Nebraska. The model was calibrated to match groundwater-level and base-flow data from the stream-aquifer system from pre-1940 through 2010 (including predevelopment [pre-1895], early development [1895-1940], and historical development [1940 through 2010] conditions) using an automated parameter-estimation method. The calibrated model then was used to simulate hypothetical development conditions (2011 through 2060). Predicted changes to stream base flow based on simulated changes to groundwater withdrawal will aid in developing strategies for management of hydrologically connected water supplies. Additional wells were simulated throughout the model domain and pumped for 50 years to assess the effect of wells on aquifer depletions, including stream base flow. The percentage of withdrawal for each well after 50 years, which was compensated by aquifer reductions to stream base flow, storage, or evapotranspiration, was computed and mapped. These depletions are influenced by aquifer properties, time, and distance from the well. Stream base-flow depletion results showed that the closer the added well was to a stream, the greatest the effect on the stream base flow. Areas of stream base-flow depletion percentages greater than 80 percent were generally within 1 mile (mi) from the stream. The distance increased to 6 mi near the confluence of the Dismal and Middle Loup Rivers, and the North Loup and Calamus Rivers. The percentage of stream base-flow depletion decreased as the distance from the stream increased. Areas more than 10 mi from the stream generally had a stream base-flow depletion of 10 percent or less. Evapotranspiration depletion was largest in areas closest to streams, specifically in the Elkhorn River watershed. It was also larger in areas of interdunal wetlands within the Sand Hills. Evapotranspiration depletion was negligible in areas greater than 5 mi from a stream, with the exception of interdunal areas in Cherry, Grant, and Arthur Counties. The storage depletion percentage increased as the distance from a stream increased. Storage depletion was largest in areas between streams. Areas experiencing the smallest amount of storage depletion were adjacent to streams. Calibrated model outputs and streamflow depletion analysis are publicly available online. Accuracy of the simulations is affected by input data limitations, system simplifications, assumptions, and resources available at the time of the simulation construction and calibration. Most of the important limitations relate either to data used as simulation inputs or to data used to estimate simulation inputs. Development of the regional simulations focused on generalized hydrogeologic characteristics within the study area and did not attempt to describe variations important to local-scale conditions. These simulations are most appropriate for analyzing groundwater-management scenarios for large areas and during long periods and are not suitable for analysis of small areas or short periods.

ABSTRACT:

To assess the effect that increased water use is having on the long-term availability of groundwater within the Ozark Plateaus aquifer system, a groundwater-flow model was developed using MODFLOW 2000 for a model area covering 7,340 square miles for parts of Arkansas, Kansas, Missouri, and Oklahoma. Vertically the model is divided into five units. From top to bottom these units of variable thickness are: the Western Interior Plains confining unit, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, and the St. Francois confining unit. Large mined zones contained within the Springfield Plateau aquifer are represented in the model as extensive voids with orders-of-magnitude larger hydraulic conductivity than the adjacent nonmined zones. Water-use data were compiled for the period 1960 to 2006, with the most complete data sets available for the period 1985 to 2006. In 2006, total water use from the Ozark aquifer for Missouri was 87 percent (8,531,520 cubic feet per day) of the total pumped from the Ozark aquifer, with Kansas at 7 percent (727,452 cubic feet per day), and Oklahoma at 6 percent (551,408 cubic feet per day); water use for Arkansas within the model area was minor. Water use in the model from the Springfield Plateau aquifer in 2005 was specified from reported and estimated values as 569,047 cubic feet per day. Calibration of the model was made against average water-level altitudes in the Ozark aquifer for the period 1980 to 1989 and against waterlevel altitudes obtained in 2006 for the Springfield Plateau and Ozark aquifers. Error in simulating water-level altitudes was largest where water-level altitude gradients were largest, particularly near large cones of depression. Groundwater flow within the model area occurs generally from the highlands of the Springfield Plateau in southwestern Missouri toward the west, with localized flow occurring towards rivers and pumping centers including the five largest pumping centers near Joplin, Missouri; Carthage, Missouri; Noel, Missouri; Pittsburg, Kansas; and Miami, Oklahoma. Hypothetical scenarios involving various increases in groundwater-pumping rates were analyzed with the calibrated groundwater-flow model to assess changes in the flow system from 2007 to the year 2057. Pumping rates were increased between 0 and 4 percent per year starting with the 2006 rates for all wells in the model. Sustained pumping at 2006 rates was feasible at the five pumping centers until 2057; however, increases in pumping resulted in dewatering the aquifer and thus pumpage increases were not sustainable in Carthage and Noel for the 1 percent per year pumpage increase and greater hypothetical scenarios, and in Joplin and Miami for the 4 percent per year pumpage increase hypothetical scenarios. Zone-budget analyses were performed to assess the groundwater flow into and out of three zones specified within the Ozark-aquifer layer of the model. The three zones represented the model part of the Ozark aquifer in Kansas (zone 1), Oklahoma (zone 2), and Missouri and Arkansas (zone 3). Groundwater pumping causes substantial reductions in water in storage and induces flow through the Ozark confining unit for all hypothetical scenarios evaluated. Net simulated flow in 2057 from Kansas (zone 1) to Missouri (zone 3) ranges from 74,044 cubic feet per day for 2006 pumping rates (hypothetical scenario 1) to 625,319 cubic feet per day for a 4 percent increase in pumping per year (hypothetical scenario 5). Pumping from wells completed in the Ozark aquifer is the largest component of flow out of zone 3 in Missouri and Arkansas, and varies between 88 to 91 percent of the total flow out of zone 3 for all of the hypothetical scenarios. The largest component of flow into Oklahoma (zone 2) comes from the overlying Ozark confining unit, which is consistently about 45 percent of the total. Flow from the release of water in storage, from general-head boundaries, and from zones 1 and 3 is considerably smaller values that range from 3 to 22 percent of the total flow into zone 2. The largest flow out of the Oklahoma part of the model occurs from pumping from wells and ranges from 52 to 69 percent of the total.

ABSTRACT:

HYDROLOGIC MODEL OF BIG BEND GROUNDWATER MANAGEMENT DISTRICT NO. 5

ABSTRACT:

The Propopis tamarugo Phil, also known as Tamarugo, is an endemic and protected tree that survives in the Atacama Desert-a hyper arid and highly saline environment. The Tamarugo is threatened because of groundwater overexploitation, and its preservation depends on the soil moisture in the vadose zone, as many of the tree roots do not reach the current water table levels. To improve the estimation of soil moisture available for the Tamarugo trees, we applied a hydrogeological model that couples the unsaturated and saturated zones. The model was used to represent different groundwater exploitation and recharge scenarios between February 2006 and September 2030 to predict simultaneously groundwater levels and soil moisture. The model results show that even at locations where water table depletion is relatively small (1-1.5 m), soil moisture can drastically decrease (0.25-0.30 m(3)/m(3)). Therefore, Tamarugo survival can be better addressed, as the applied model provides a management tool to estimate response of Tamarugo trees to changing soil moisture. To further improve the model and its use to assess Tamarugo survival, more field data, such as soil hydrodynamic properties and soil moisture, should be collected. Additionally, relationships between the state of the Tamarugo trees and soil moisture should be further constructed. In this way, the developed model will be able to predict future conditions associated to the Tamarugo's health state.

ABSTRACT:

The city of Sioux Falls, in southeastern South Dakota, is the largest city in South Dakota. The U.S. Geological Survey (USGS), in cooperation with the city of Sioux Falls, completed a groundwater-flow model to use for improving the understanding of groundwater-flow processes, estimating hydrogeologic properties, and analyzing groundwater and surface-water interactions for the Big Sioux aquifer in the model area. The model area includes the Big Sioux aquifer and the underlying hydrogeologic units from Dell Rapids, South Dakota, to the confluence of the Big Sioux River and the outlet of the Sioux Falls Diversion Channel in eastern Sioux Falls, S. Dak. The Big Sioux aquifer is the primary aquifer in the model area and the focus of the groundwater-flow model. The Big Sioux River is the largest stream in the model area and is in hydraulic connection with the Big Sioux aquifer. A conceptual model for the area was constructed and includes a characterization of the hydrogeologic framework, analysis and construction of potentiometric surfaces, and summary of estimated water budget components in the model area. The primary hydrogeologic units in the model area consist of (1) the Big Sioux aquifer, (2) a glacial till confining unit, and (3) bedrock aquifers (Split Rock Creek and Sioux Quartzite aquifers). Sources of groundwater recharge included infiltration of precipitation, stream seepage, and groundwater exchanges among the hydraulically connected Big Sioux aquifer, glacial till confining unit, and bedrock aquifers. Groundwater losses included evapotranspiration, groundwater discharge to streams, and groundwater withdrawal to supply water-use needs. A numerical groundwater-flow model (numerical model) was constructed and was used to simulate all aspects of the conceptual model for predevelopment (steady-state) and time-varying (transient) monthly conditions for 1950-2017. The numerical model was constructed using the USGS modular hydrologic simulation program, MODFLOW-6, and was calibrated using the Parameter ESTimation software, PEST++. The transient numerical model was calibrated for steady-state and transient monthly conditions for 1950-2017. Calibration targets were observations of hydraulic head, changes in hydraulic head, monthly mean streamflow (as a rate), and cumulative monthly stream discharge (as a volume). Parameters adjusted during model calibration were horizontal and vertical hydraulic conductivity, specific storage, specific yield, recharge and evapotranspiration multipliers, and streambed hydraulic conductivity. Horizontal and vertical hydraulic conductivity were estimated at pilot points distributed within the model area; specific storage and specific yield were assigned to uniform values in each layer in the model area; recharge and evapotranspiration multipliers were assigned uniformly for every stress period in the numerical model; and streambed hydraulic conductivity values were assigned uniformly between stream confluences. The final calibrated parameter values of horizontal and vertical hydraulic conductivity, specific yield, specific storage, streambed hydraulic conductivity, recharge, and evapotranspiration were considered reasonable for the hydrogeologic materials and conditions in the model area for 1950-2017. Overall, simulated hydraulic head altitudes had a linear regression coefficient of determination (R2) of 0.48. Hydraulic head altitude residuals for the glacial till confining unit and bedrock aquifers were typically greater in magnitude when compared to residuals in the Big Sioux aquifer, but simulated hydraulic head altitudes in the Big Sioux aquifer compared favorably with mean observed hydraulic head altitudes and had a linear regression R2 of 0.93. Simulated streamflow hydrographs matched the general trends of observed increases and decreases in streamflow for USGS streamgages 06482000 (Big Sioux River at Sioux Falls, S. Dak.) and 06482020 (Big Sioux River at North Cliff Avenue at Sioux Falls, S. Dak.), but larger streamflows were overestimated at the first streamgage and underestimated at the second streamgage. The numerical model reasonably estimated cumulative monthly stream discharge for the first 10-15 years of available streamflow records at both USGS streamgages. After the first 10-15 years of available streamflow record, cumulative monthly stream discharge was closely estimated for USGS streamgage 06482000 and underestimated at USGS streamgage 06482020. Composite sensitivities without regularization were calculated by PEST++ for the calibrated numerical model parameters and were averaged by parameter group. The parameter group with the highest mean composite sensitivity was the recharge multiplier parameter group. Model simplifications, assumptions, and limitations were necessary for construction of the conceptual and numerical models and for calibration efficiency. Spatial simplification of hydraulic properties could cause the numerical model to misrepresent reactions to changes in localized stresses, such as additional demands for groundwater withdrawal. The numerical model was temporally discretized into monthly periods and required scaling daily rates into representative monthly rates for model input and calibration targets. Based on the comparison between the observed and simulated groundwater levels, monthly mean streamflow and cumulative monthly stream discharge, and general groundwater distribution and flow, the numerical model favorably simulated the flow in the Big Sioux aquifer. Eventual capture was calculated in the model area using a steady-state numerical groundwater-flow model. The eventual capture map shows areas of higher streamflow capture adjacent to the Big Sioux River north of the city of Sioux Falls and along the lower part of the Sioux Falls Diversion Channel, and areas of lower streamflow capture along aquifer boundaries and near the southern Sioux Quartzite barrier. The timing of capture was determined using a transient numerical groundwater-flow model to determine the likely captured water sources for 30 years of groundwater withdrawal at three hypothetical wells using three continuous withdrawal rates (112.5, 450.0, and 900.0 gallons per minute). Supply for all three hypothetical wells became capture-dominated after only a short period of continuous withdrawal. Capture stabilized after about 10-15 years for well A, and after 20-25 years for well B, and after about 10-15 years for well C. The groundwater-flow model is a suitable tool to use for improving the understanding of groundwater-flow processes, estimating hydrogeologic properties, and analyzing groundwater and surface-water interactions for the Big Sioux aquifer near Sioux Falls, S. Dak. The numerical model can be used to simulate hydrologic scenarios, advance understanding of groundwater budgets, compute system response to stress, and determine likely sources of water supplied to wells.

ABSTRACT:

In order to better represent the configuration of the stream network and simulate local groundwater-surface water interactions, a version of MODFLOW with refined spacing in the topmost layer was applied to a Lake Michigan Basin (LMB) regional groundwaterflow model developed by the U. S. Geological. Regional MODFLOW models commonly use coarse grids over large areas; this coarse spacing precludes model application to local management issues (e. g., surface-water depletion by wells) without recourse to labor-intensive inset models. Implementation of an unstructured formulation within the MODFLOW framework (MODFLOW-USG) allows application of regional models to address local problems. A "semi-structured" approach (uniform lateral spacing within layers, different lateral spacing among layers) was tested using the LMB regional model. The parent 20-layer model with uniform 5000-foot (1524-m) lateral spacing was converted to 4 layers with 500-foot (152-m) spacing in the top glacial (Quaternary) layer, where surface water features are located, overlying coarser resolution layers representing deeper deposits. This semi-structured version of the LMB model reproduces regional flow conditions, whereas the finer resolution in the top layer improves the accuracy of the simulated response of surface water to shallow wells. One application of the semi-structured LMB model is to provide statistical measures of the correlation between modeled inputs and the simulated amount of water that wells derive from local surface water. The relations identified in this paper serve as the basis for metamodels to predict (with uncertainty) surface-water depletion in response to shallow pumping within and potentially beyond the modeled area, see Fienen et al. (2015a).

ABSTRACT:

Distributed numerical models, considered as optimal tools for groundwater resources management, have always been constrained by availability of spatio-temporal input data. This problem is particularly distinct in arid and semi-arid developing countries, characterized by large spatio-temporal variability of water fluxes but scarce ground-based monitoring networks. That problem can be mitigated by remote sensing (RS) methods, which nowadays are applicable for modelling not only surface-water but also groundwater resources, through rapidly increasing applications of integrated hydrological models (IHMs). This study shows implementation of various RS products in the IHM of the Central Kalahari Basin (similar to 200 Mm(2)) multi-layered aquifer system, characterized by semi-arid climate and thick unsaturated zone, both enhancing evapotranspiration. The MODFLOW-NWT model with UZF1 package, accounting for variably saturated flow, was set up and calibrated in transient conditions throughout 13.5 years using borehole hydraulic heads as state variables and RS-based daily rainfall and potential evapotranspiration as driving forces. Other RS input data included: digital-elevation-model, land-use/land-cover and soils datasets. The model characterized spatio-temporal water flux dynamics, providing 13-year (2002-2014) daily and annual water balances, thereby evaluating groundwater-resource dynamics and replenishment. The balances showed the dominant role of evapotranspiration in restricting gross recharge to only a few mm yr(-1) and typically negative net recharge (median,-1.5 mm yr(-1)), varying from -3.6 (2013) to +3.0 (2006) mm yr(-1) (rainfall of 287 and 664 mm yr(-1) respectively) and implying systematic water-table decline. The rainfall, surface morphology, unsaturated zone thickness and vegetation type/density were primary determinants of the spatio-temporal net recharge distribution.

ABSTRACT:

Study region: East African Rift Valley basin. Study focus: Water availability in the rift valley relies heavily on the discharge from the highlands to rivers that run to the rift floor. This research explores the effect of Land use/Land cover (LULC) and climate change on water yield and groundwater recharge (WYGR) using coupled SWAT-MODFLOW, which integrates Soil and Water Assessment Tool (SWAT) and Newton Modular Finite Difference Groundwater Flow (MODFLOW-NWT). The LULC change was analyzed using artificial neural network-based cellular automata. New hydrological insights: The dominant LULC is cultivated land and expanded by 5% to the forest and grassland areas. The average temperature and precipitation are expected to rise by 8-11% and 3-6%, respectively. Climate change affects the spatiotemporal distribution of WYGR significantly, while LULC change has a trivial effect. Under the baseline scenario, the recharge was 10% of the average annual precipitation, but climate change is projected to reduce it by 47-53%. Water yield reduction up to 48% and change of perennial rivers to intermittent are expected in the coming decades. The region will experience water scarcity, emerging mainly from climate change.

ABSTRACT:

Groundwater models often serve as management tools to evaluate competing water uses including ecosystems, irrigated agriculture, industry, municipal supply, and others. Depletion potential mapping-showing the model-calculated potential impacts that wells have on stream baseflow-can form the basis for multiple potential management approaches in an oversubscribed basin. Specific management approaches can include scenarios proposed by stakeholders, systematic changes in well pumping based on depletion potential, and formal constrained optimization, which can be used to quantify the tradeoff between water use and stream baseflow. Variables such as the maximum amount of reduction allowed in each well and various groupings of wells using, for example, K-means clustering considering spatial proximity and depletion potential are considered. These approaches provide a potential starting point and guidance for resource managers and stakeholders to make decisions about groundwater management in a basin, spreading responsibility in different ways. We illustrate these approaches in the Little Plover River basin in central Wisconsin, United States-home to a rich agricultural tradition, with farmland and urban areas both in close proximity to a groundwater-dependent trout stream. Groundwater withdrawals have reduced baseflow supplying the Little Plover River below a legally established minimum. The techniques in this work were developed in response to engaged stakeholders with various interests and goals for the basin. They sought to develop a collaborative management plan at a watershed scale that restores the flow rate in the river in a manner that incorporates principles of shared governance and results in effective and minimally disruptive changes in groundwater extraction practices.

ABSTRACT:

The Atlantis Water Supply Scheme (AWSS, Western Cape, South Africa) has been in operation for about 40 years as a means to supply and augment drinking water to the town of Atlantis via managed aquifer recharge (MAR). In this study, the numerical model MODFLOW for groundwater flow and contaminant transport was used in support of the management of the AWSS. The aims were: (i) to calibrate the MODFLOW model for the MAR site at Atlantis; (ii) to run realistic scenarios that cannot be replicated through experiments; and (iii) to make recommendations in support of efficient and sustainable management of the aquifer. MODFLOW was calibrated through comparison of observed and simulated groundwater levels (R-2 between 0.663 and 0.995). Scenario simulations indicated possible drawdowns between < 5 m (low groundwater abstraction and low artificial recharge of groundwater through infiltration basins) and > 20 m (high abstraction and high artificial recharge) at localized areas of the Witzand wellfield. At Silwerstroom, large drawdown levels were not predicted to occur, so this wellfield could be exploited more without affecting the sustainability of the groundwater resource. Groundwater moves from the infiltration basins towards the Witzand wellfield at a rate of 120-150 m.a(-1). The modelling results supported recommendations for balancing groundwater abstraction and artificial recharge volumes, monitoring the water balance components of the system, the potential risks of groundwater contamination and the delineation of groundwater protection zones.

ABSTRACT:

A groundwater-flow model was developed for the Bad River Watershed and surrounding area by using the U.S. Geological Survey (USGS) finite-difference code MODFLOW-NWT. The model simulates steady-state groundwater-flow and base flow in streams by using the streamflow routing (SFR) package. The objectives of this study were to: (1) develop an improved understanding of the groundwater-flow system in the Bad River Watershed at the regional scale, including the sources of water to the Bad River Band of Lake Superior Chippewa Reservation (Reservation) and groundwater/surface-water interactions; (2) provide a quantitative platform for evaluating future impacts to the watershed, which can be used as a starting point for more detailed investigations at the local scale; and (3) identify areas where more data are needed. This report describes the construction and calibration of the groundwater-flow model that was subsequently used for analyzing potential locations for the collection of additional field data, including new observations of water-table elevation for refining the conceptualization and corresponding numerical model of the hydrogeologic system. The study area can be conceptually divided into three primary hydrogeologic environments. The first encompasses the southern uplands with relatively low topographic relief, where groundwater-flow is unconfined and occurs primarily in sandy till and glacial outwash overlying Archean-aged crystalline bedrock. The second includes a transitional area of higher topographic relief and shallow depth to bedrock, in the vicinity of ridges formed by steeply dipping, early-Proterozoic aged metasedimentary units of the Marquette Range Supergroup (including the Ironwood Formation), and late-Proterozoic igneous units associated with the Midcontinent Rift System (MRS). Groundwater-flow in this area likely occurs primarily through connected networks of bedrock fractures that are not well characterized, and also in isolated pockets of Quaternary deposits. The third and last hydrogeologic environment includes lowlands along Lake Superior where a deep sandstone aquifer is confined by thick deposits of clay-rich till. Model input was compiled by using both published and unpublished data. Constant flux boundary conditions for the model perimeter were developed from a regional analytic element model described in appendix 1 of this report. Pumping from 26 high-capacity wells within the model area was included. The SFR stream network was developed from the National Hydrography Dataset (NHDPlus Version 2) and hydrography from the Wisconsin Department of Natural Resources (WDNR). Hydraulic conductivity values were determined for each model cell by interpolation from a network of pilot points, within zones representing major hydrogeologic units. Recharge to the groundwater system was estimated on a cell-by-cell basis by using the Soil Water Balance code (SWB), with gridded daily temperature and precipitation data for the period 1980-2011, and GIS coverages of soil and land-surface conditions. Estimated recharge varies considerably, following spatial patterns in the precipitation and soil hydrologic group inputs. The lowest recharge values occur in the Superior lowlands, whereas the highest values occur in the upland areas, especially those underlain by sandy soils, and in the vicinity of bedrock hills. The model was calibrated to groundwater-levels and base flows obtained from the USGS National Water Information System (NWIS) database, and groundwater-levels obtained from the WDNR and Band River Band well-construction databases. Calibration was performed via nonlinear regression by using the parameter-estimation software suite PEST. Groundwater levels and base-flow observations in the calibration dataset were well simulated by the calibrated model, with reasonable values of hydraulic conductivity. The pilot-point parameters that were most constrained by observations during model calibration coincided with the locations containing the most wells (head observations) especially the population centers of Ashland, Mellen, and other communities along the major highway corridors. Results from the calibrated model illustrate differences in the nature of groundwater-?ow within the watershed. In the southern part of the watershed, where bedrock is shallow, groundwater ?ow paths are relatively short, extending from local recharge areas to adjacent ?rst and second-order streams. In contrast, laterally continuous deposits of clay-rich till covering the Superior Lowlands isolate most smaller streams from the sandstone aquifer, allowing for longer ?ow paths toward larger streams such as the Bad, Marengo, and White Rivers. Approximately three-quarters of all ?rst-order stream cells were dry in the Superior Lowlands, compared to only half of ?rst-order stream cells in the southern bedrock uplands. The model was used to delineate the groundwatershed for the Bad and Kakagon Rivers. Groundwatershed is defned as the area contributing groundwater discharge to one of these streams and their tributaries. The groundwatershed was found to align closely with the surface-watershed, with the most notable exception occurring along the southwestern half of Birch Hill, where surface water drains southwest towards the Potato River, and groundwater ?ows north and east towards Lake Superior. Similarly, the contributing area of groundwater-?ow to the Reservation was delineated. Results indicate the off-Reservation groundwater contributing area to be limited in comparison to the extent of the watershed, extending southward into the highlands underlain by MRS igneous rock units, but not further into the area underlain by the Marquette Range Supergroup. Stable isotope samples were collected from 54 wells within the watershed, to investigate sources of groundwater. Oxygen-18 (? 18O) values lower than -13.0 per mil were documented in the sampling, and likely indicate the presence of recharge water from the last glacial period (>9,500 years old) beneath the northern portion of the Reservation, in the vicinity of Odanah, Wisconsin. Finally, a new data-worth analysis of potential new monitoring-well locations was performed by using the model. The relative worth of new measurements was evaluated based on their ability to increase con?dence in model predictions of groundwater levels and base ?ows at 35 locations, under the condition of a proposed open-pit iron mine. Results of the new data-worth analysis, and other inputs and outputs from the Bad River model, are available through an online dynamic web mapping service at (http://wim.usgs.gov/badriver/).

ABSTRACT:

Transient recharge to the water table is often not well understood or quantified. Two approaches for simulating transient recharge in a ground water flow model were investigated using the Trout Lake watershed in north-central Wisconsin: ( 1) a traditional approach of adding recharge directly to the water table and ( 2) routing the same volume of water through an unsaturated zone column to the water table. Areas with thin ( less than 1 m) unsaturated zones showed little difference in timing of recharge between the two approaches; when water was routed through the unsaturated zone, however, less recharge was delivered to the water table and more discharge occurred to the surface because recharge direction and magnitude changed when the water table rose to the land surface. Areas with a thick ( 15 to 26 m) unsaturated zone were characterized by multimonth lags between infiltration and recharge, and, in some cases, wetting fronts from precipitation events during the fall overtook and mixed with infiltration from the previous spring snowmelt. Thus, in thicker unsaturated zones, the volume of water infiltrated was properly simulated using the traditional approach, but the timing was different from simulations that included unsaturated zone flow. Routing of rejected recharge and ground water discharge at land surface to surface water features also provided a better simulation of the observed flow regime in a stream at the basin outlet. These results demonstrate that consideration of flow through the unsaturated zone may be important when simulating transient ground water flow in humid climates with shallow water tables.

ABSTRACT:

Understanding the fresh groundwater lens (FGL) behavior and potential threat of climatic-induced seawater intrusion (SWI) are significant for the future water resources management of many small islands. In this paper, the FGL of Kish Island, an arid-region case in the Persian Gulf, Iran, is modeled using two-dimensional (2D) and three-dimensional (3D) simulations. These simulations are based on the application of SUTRA, a density-dependent groundwater numerical model. Also, the numerical model parameters are calibrated using PEST, an automated parameter estimation code. Firstly a detailed conceptualization of the FGL model is completed to understand the sensitivity of the FGL to some particular aspects of the model prior to analysis of climate change simulations. For these investigations, the FGL system is defined based on Kish Island system to accomplish the integrated comparison of features of a conceptual model that are representative of real-world systems. This is the first study which adopts such an approach. The comparison of cross-sectional simulations suggests that the two-layer properties of the Kish Island aquifer have a significant influence on the FGL while the impacts of lateral-boundary irregularities are negligible. The impacts of sea-level rise (SLR), associated land-surface inundation (LSI), and variations in recharge rate on the FGL salinization of Kish Island are investigated numerically. Variations of SLR value (1-4 m) and net recharge rate (17-24 mm/year) are considered to cover a possible range of climatic scenarios in this arid-region island. The 2D and 3D simulation results demonstrate that LSI caused by SLR and recharge rate variation impacts are more important factors in the FGL in comparison to estimated SLR impacts without LSI. It is also shown that climate change impacts on the FGL are long-term to reach a new FGL equilibrium in the case of Kish Island's aquifer system. The comparative analysis of 2D and 3D results shows that three-dimensionality is a significant factor, especially in large-scale 3D systems of small islands. The results of this study are expected to have implications for the understanding and management of the fresh groundwater resources of Kish Island and are also expected to be relevant to the study of the impact of climate change on groundwater resources on islands worldwide. (C) 2014 Elsevier B.V. All rights reserved.

ABSTRACT:

During the 1990s, groundwater overexploitation has resulted in seawater intrusion in the coastal aquifer of the Shenzhen city, China. Although water supply facilities have been improved and alleviated seawater intrusion in recent years, groundwater overexploitation is still of great concern in some local areas. In this work we present a three-dimensional density-dependent numerical model developed with the FEFLOW code, which is aimed at simulating the extent of seawater intrusion while including tidal effects and different groundwater pumping scenarios. Model calibration, using waterheads and reported chloride concentration, has been performed based on the data from 14 boreholes, which were monitored from May 2008 to December 2009. A fairly good fitness between the observed and computed values was obtained by a manual trial-and-error method. Model prediction has been carried out forward 3 years with the calibrated model taking into account high, medium and low tide levels and different groundwater exploitation schemes. The model results show that tide-induced seawater intrusion significantly affects the groundwater levels and concentrations near the estuarine of the Dasha river, which implies that an important hydraulic connection exists between this river and groundwater, even considering that some anti-seepage measures were taken in the river bed. Two pumping scenarios were considered in the calibrated model in order to predict the future changes in the water levels and chloride concentration. The numerical results reveal a decreased tendency of seawater intrusion if groundwater exploitation does not reach an upper bound of about 1.32 x 10(4) m(3)/d. The model results provide also insights for controlling seawater intrusion in such coastal aquifer systems.

ABSTRACT:

The control and management of seawater intrusion in coastal aquifers is a major challenge in the field of water resources management. Seawater intrusion is a major problem in the coastal aquifer of Wadi Ham, United Arab Emirates, caused by intensive groundwater abstraction from increased agricultural activities. This has caused the abandonment of salinized wells and ultimately affected farming activities and domestic water supply in the area. In this study, the 3D finite element groundwater flow and solute transport model is developed using FEFLOW to simulate pumping of brackish water from the intrusion zone to control seawater intrusion in the aquifer. The model was calibrated and validated with available records of groundwater levels and salinity distribution. Different simulation scenarios were conducted to obtain optimum pumping locations, rates as well as a number of wells. A comparison between scenarios of non-pumping and pumping of brackish water was conducted. Results showed an increase in the concentration of groundwater salinity under the non-pumping scenario, while it decreased under the pumping scenario. Under the non-pumping scenario, isoline 30,000 mgl(-1) was observed to have intruded into the south-eastern part of the aquifer, while the maximum isoline observed for the same area under the pumping scenario was 20,000 mgl(-1). This result showed an overall improvement in the quality of groundwater and ultimately halted seawater intrusion in the aquifer.

ABSTRACT:

A stochastic study of long-term forecasts of seawater intrusion with an application to the Korba aquifer (Tunisia) is presented. Firstly, a geostatistical model of the exploitation rates was constructed, based on a multi-linear regression model combining incomplete direct data and exhaustive secondary information. Then, a new method was designed and used to construct a geostatistical model of the hydraulic conductivity field by combining lithological information and data from hydraulic tests. Secondly, the effects of the uncertainties associated with the pumping rates and the hydraulic conductivity field on the 3D density-dependent transient model were analysed separately and then jointly. The forecasts of the impacts of two different management scenarios on seawater intrusion in the year 2048 were performed by means of Monte Carlo simulations, accounting for uncertainties in the input parameters as well as possible changes of the boundary conditions. Combining primary and secondary data allowed maps of pumping rates and the hydraulic conductivity field to be constructed, despite a lack of direct data. The results of the stochastic long-term forecasts showed that, most probably, the Korba aquifer will be subject to important losses in terms of regional groundwater resources.

ABSTRACT:

The Moghra aquifer has shown promise in land reclamation projects conducted in the Western Desert of Egypt. Although this aquifer has hundreds of pumping wells in new urban communities built to meet the needs of the increased population, the system is threatened by the phenomenon of seawater intrusion (SWI). The present study evaluates the degree to which these pumping wells will attract seawater to the aquifer system in the Western Desert region under different pumping conditions. Using the SEAWAT module of Groundwater Modeling System (GMS) software, a three-dimensional (3D) finite-difference model is built to simulate the flow and salinity distribution in the Moghra aquifer considering the geological and hydrogeological characteristics of the aquifer system. The procedure used to solve the mathematical model relied on merging two different approaches. The first approach described the dividing lines of the transition zone due to the SWI. The second approach was applied to conduct the perfect calibration process for the aquifer system. The results show that the flow and quality of the groundwater aquifer are affected by pumping. The water level and salinity are predicted under different pumping rates, a fivefold increase in the pumping rate results that the salinity increased between 4% and 26.8% according to the well location. Moreover, the drawdown values reached 162 m, which is about 46.3% of the saturated thickness.

ABSTRACT:

During the last years, we have developed a model, which is able to simulate hydrological processes at a Pan-European scale. The model has multiple possible uses, including flood forecasting, identification of groundwater recharge / discharge zones and large-scale water resources management. The integrated model is based on the LISFLOOD model, which simulates hydrological processes with a focus on snow and soil hydrology and streamflow routing. The area of interest is the full European continent, divided in 5 x 5 km cells. A conceptual 2D MODFLOW model was linked to improve groundwater simulation. With this coupling, it is now possible to simulate the water exchanges between adjacent cells, and between groundwater and river. Available meteorological data from 1-1-1990 to 31-10-2014 were used as input for the coupled model, together with values of aquifer properties derived from literature. We used observed data of recharge, discharge and hydraulic heads from the Danube river basin to check if the model results correspond to reality. The results show a reasonably high degree of agreement between observed and simulated data, taking into account the limitations of large scale modelling. This model is the first step to improve integrated groundwater and surface water modelling which includes the collection of data and the production of Pan-European groundwater parameter maps.

ABSTRACT:

Applying the Terrestrial Systems Modeling Platform, TSMP, this study provides the first simulated long-term (1996-2018), high-resolution (~12.5?km) terrestrial system climatology over Europe, which comprises variables from groundwater across the land surface to the top of the atmosphere (G2A). The data set offers an unprecedented opportunity to test hypotheses related to short- and long-range feedback processes in space and time between the different interacting compartments of the terrestrial system. The physical consistency of simulated states and fluxes in the terrestrial system constitutes the uniqueness of the data set: while most regional climate models (RCMs) have a tendency to simplify the soil moisture and groundwater representation, TSMP explicitly simulates a full 3D soil- and groundwater dynamics, closing the terrestrial water cycle from G2A. As anthopogenic impacts are excluded, the dataset may serve as a near-natural reference for global change simulations including human water use and climate change. The data set is available as netCDF files for the pan-European EURO-CORDEX domain.

ABSTRACT:

The Wadi Watir delta, in the arid Sinai Peninsula, Egypt, contains an alluvial aquifer underlain by impermeable Precambrian basement rock. The scarcity of rainfall during the last decade, combined with high pumping rates, resulted in degradation of water quality in the main supply wells along the mountain front, which has resulted in reduced groundwater pumping. Additionally, seawater intrusion along the coast has increased salinity in some wells. A three-dimensional (3D) groundwater flow model (MODFLOW) was calibrated using groundwater-level changes and pumping rates from 1982 to 2009; the groundwater recharge rate was estimated to be 1.58 x 10(6) m(3)/year. A variable-density flow model (SEAWAT) was used to evaluate seawater intrusion for different pumping rates and well-field locations. Water chemistry and stable isotope data were used to calculate seawater mixing with groundwater along the coast. Geochemical modeling (NETPATH) determined the sources and mixing of different groundwaters from the mountainous recharge areas and within the delta aquifers; results showed that the groundwater salinity is controlled by dissolution of minerals and salts in the aquifers along flow paths and mixing of chemically different waters, including upwelling of saline groundwater and seawater intrusion. Future groundwater pumping must be closely monitored to limit these effects.

ABSTRACT:

Over the past few decades, seawater desalination has become a necessity for freshwater supply in many countries worldwide, particularly in arid and semi-arid regions. One potentially high-quality feed water for desalination is saline groundwater (SGW) from coastal aquifers, which has lower fouling propensity than seawater. This study examines the effect of pumping SGW from a phreatic coastal aquifer on fresh groundwater, particularly on the dynamics of the fresh-saline water interface (FSI). Initially, we constructed a 3D finite-element model of a phreatic coastal aquifer by using the FEFLOW software, which solves the coupled variable density groundwater flow and solute transport equations. Then, we compared and validated the results of the model to those of a field-scale pumping test. The model indicates that pumping SGW from a coastal aquifer freshens the aquifer and rehabilitates parts that were salinized due to seawater intrusion - an effect that increases with increasing pumping rate. In addition, when simultaneously pumping fresh groundwater further inland and SGW from below the FSI, the freshening effect is less pronounced and the salinity of the aquifer is more stable. In line with the results of the model, the field experiment revealed that salinity in the observation well decreases over the course of pumping. Taken together, our findings demonstrate that, in addition to providing a high-quality source feed water for desalination, pumping SGW does not salinize the aquifer and even rehabilitates it by negating the effect of seawater intrusion. These findings are important for planning shoreline desalination facilities and for managing arid coastal regions with lack of water supply and over exploited aquifers. (C) 2019 Published by Elsevier Ltd.

ABSTRACT:

This study tests for the first time the long-term effects of pumping saline groundwater (SGW) as feed for a desalination plant on a coastal aquifer. Field measurements combined with 3D modeling of the hydrological conditions were conducted to examine the effects of SGW pumping on the aquifer system. The plant is next to the city of Almeria (South East Spain) and has been operating since 2006. It uses multiple beach wells along the shore to draw SGW from beneath the fresh-saline water interface (FSI) of the Andarax coastal aquifer. The long-term impact of the intensive pumping on the aquifer was assessed by electrical conductivity profiles in three observation wells dining 12 years of pumping. The FSI deepened with continuous pumping, reaching a decrease of similar to 50 m in the observation well closest to the pumping wells. A calibrated three-dimensional numerical model of the Anthrax aquifer replicates the freshening of the aquifer due to the continuous pumping, resulting in a salinity decrease of similar to 16% in the vicinity of the wells. The salinity decrease stabilizes at 17%, and the model predicts no further significant decrease in salinity for additional 20 years. Submarine groundwater discharge is lowered due to the SGW pumping and similar to 19,000,000 m(3) of freshwater has not lost to the sea during the 12 years of pumping with a rate of similar to 1,100,000 m(3) yr(-1) after 6 years of pumping. After pumping cessation, hydrostatic equilibrium would take about 20 years to recover. This work presents the complex dynamics of the HI due to the SGW pumping for desalination in the first real long-term scenario. It shows by combining field work and numerical modeling, a significant freshening of the aquifer by pumping SGW, emphasizing an additional advantage and the effectiveness of this use as a negative hydraulic barrier against seawater intrusion. (C) 2020 Elsevier B.V. All rights reserved.

ABSTRACT:

Climate change is expected to induce sea level rise in the German Bight, which is part of the North Sea, Germany. Climate change may also modify river discharge of the river Weser flowing into the German Bight, which will alter both pressure and salinity distributions in the river Weser estuary. To study the long-term interaction between sea level rise, discharge variations, a storm surge and coastal aquifer flow dynamics, a 3D seawater intrusion model was designed using the fully coupled surface-subsurface numerical model HydroGeoSphere. The model simulates the coastal aquifer as an integral system considering complexities such as variable-density flow, variably saturated flow, irregular boundary conditions, irregular land surface and anthropogenic structures (e.g., dyke, drainage canals, water gates). The simulated steady-state groundwater flow of the year 2009 is calibrated using PEST. In addition, four climate change scenarios are simulated based on the calibrated model: (i) sea level rise of 1 m, (ii) the salinity of the seaside boundary increases by 4 PSU (Practical Salinity Units), (iii) the salinity of the seaside boundary decreases by 12 PSU, and (iv) a storm surge with partial dyke failure. Under scenarios (i) and (iv), the salinized area expands several kilometers further inland during several years. Natural remediation can take up to 20 years. However, sudden short-term salinity changes in the river Weser estuary do not influence the salinized area in the coastal aquifer. The obtained results are useful for coastal engineering practices and drinking water resource management. (C) 2015 Elsevier B.V. All rights reserved.

ABSTRACT:

In global hydrological models, groundwater (GW) is typically represented by a bucket-like linear groundwater reservoir. Reservoir models, however, (1) can only simulate GW discharge to surface water (SW) bodies but not recharge from SW to GW, (2) provide no information on the location of the GW table, and (3) assume that there is no GW flow among grid cells. This may lead, for example, to an underestimation of groundwater resources in semiarid areas where GW is often replenished by SW or to an underestimation of evapotranspiration where the GW table is close to the land surface. To overcome these limitations, it is necessary to replace the reservoir model in global hydrological models with a hydraulic head gradient-based GW flow model. We present G(3)M, a new global gradient-based GW model with a spatial resolution of 5 0 (arcminutes), which is to be integrated into the 0.5 degrees WaterGAP Global Hydrology Model (WGHM). The newly developed model framework enables in-memory coupling to WGHM while keeping overall run-time relatively low, which allows sensitivity analyses, calibration, and data assimilation. This paper presents the G3M concept and model design decisions that are specific to the large grid size required for a global-scale model. Model results under steady-state naturalized conditions, i.e., neglecting GW abstractions, are shown. Simulated hydraulic heads show better agreement to observations around the world compared to the model output of de Graaf et al. (2015). Locations of simulated SW recharge to GW are found, as is expected, in dry and mountainous regions but areal extent of SW recharge may be underestimated. Globally, GW dis-charge to rivers is by far the dominant flow component such that lateral GW flows only become a large fraction of total diffuse and focused recharge in the case of losing rivers, some mountainous areas, and some areas with very low GW recharge. A strong sensitivity of simulated hydraulic heads to the spatial resolution of the model and the related choice of the water table elevation of surface water bodies was found. We suggest to investigate how global-scale ground-water modeling at 5' spatial resolution can benefit from more highly resolved land surface elevation data.

NOTE: Model has global extent, bounding box is positioned over the Atlantic Ocean for visibility.

ABSTRACT:

Groundwater salinization is one of the most severe environmental problems in coastal aquifers worldwide, causing exceeding salinity in groundwater supply systems for many purposes. High salinity concentration in groundwater can be detected several kilometers inland and may result in an increased risk for coastal water supply systems and human health problems. This study investigates the impacts of groundwater pumping practices and regional groundwater flow dynamics on groundwater flow and salinity intrusion in the coastal aquifers of the Vietnamese Mekong Delta using the SEAWAT model-a variable-density groundwater flow and solute transport model. The model was constructed in three dimensions (3D) and accounted for multi-aquifers, variation of groundwater levels in neighboring areas, pumping, and paleo-salinity. Model calibration was carried for 13 years (2000 to 2012), and validation was conducted for 4 years (2013 to 2016). The best-calibrated model was used to develop prediction models for the next 14 years (2017 to 2030). Six future scenarios were introduced based on pumping rates and regional groundwater levels. Modeling results revealed that groundwater pumping activities and variation of regional groundwater flow systems strongly influence groundwater level depletion and saline movement from upper layers to lower layers. High salinity (>2.0 g/L) was expected to expand downward up to 150 m in depth and 2000 m toward surrounding areas in the next 14 years under increasing groundwater pumping capacity. A slight recovery in water level was also observed with decreasing groundwater exploitation. The reduction in the pumping rate from both local and regional scales will be necessary to recover groundwater levels and protect fresh aquifers from expanding paleo-saline in groundwater.

ABSTRACT:

Puri city is situated on the east coast of India, and groundwater is the only source available to meet city water supply. Due to increase in population and urbanization of the city, groundwater withdrawal is continuously increasing, which may lead to the movement of saline water interface toward the fresh groundwater. Therefore, the objective of this study was to assess the hydrodynamics of groundwater flow and to predict withdrawal for future water demand of the city without affecting the saltwater intrusion. For this, a groundwater flow model was conceptualized and validated for the present withdrawal coupled with the saltwater intrusion model. To assess the safe yield of groundwater withdrawal, various iterations were carried out with different withdrawal rates and movement of fresh and saltwater interface. This helped in quantifying the future demand of city water supply without affecting the interface between fresh groundwater and saltwater. Based on the simulation results, various measures were suggested to safeguard the groundwater resource against saltwater intrusion.

ABSTRACT:

To address concerns about the effects of water-resource management practices and rising sea level on saltwater intrusion, the U.S. Geological Survey in cooperation with the Broward County Environmental Planning and Community Resilience Division, initiated a study to examine causes of saltwater intrusion and predict the effects of future alterations to the hydrologic system on salinity distribution in eastern Broward County, Florida. A three-dimensional, variable-density solute-transport model was calibrated to conditions from 1970 to 2012, the period for which data are most complete and reliable, and was used to simulate historical conditions from 1950 to 2012. These types of models are typically difficult to calibrate by matching to observed groundwater salinities because of spatial variability in aquifer properties that are unknown, and natural and anthropogenic processes that are complex and unknown; therefore, the primary goal was to reproduce major trends and locally generalized distributions of salinity in the Biscayne aquifer. The methods used in this study are relatively new, and results will provide transferable techniques for protecting groundwater resources and maximizing groundwater availability in coastal areas. The model was used to (1) evaluate the sensitivity of the salinity distribution in groundwater to sea-level rise and groundwater pumping, and (2) simulate the potential effects of increases in pumping, variable rates of sea-level rise, movement of a salinity control structure, and use of drainage recharge wells on the future distribution of salinity in the aquifer. Results from the simulation of historical conditions indicate that the model generally represents the observed greater westward extent of elevated salinity in the central part of the intruded area relative to the northern and southernmost parts of the intruded area. Results of sensitivity testing indicate that the extent of elevated salinity is most sensitive to pumping in areas where the source of saltwater is largely offshore, from the Atlantic Ocean, and is most sensitive to sea-level rise in areas where the source of salinity is downward leakage of brackish water from canals. Simulations of future scenarios indicate that increases in pumping near the existing interface may cause the interface to advance and decreases in pumping may cause it to retreat. Climatic effects, such as periods of prolonged drought or high precipitation, may augment or counteract long-term effects of changes in pumping on aquifer salinity at well fields. With increasing rates of sea-level rise, the freshwater-saltwater interface advances progressively inland, and flow-averaged salinities at well fields near the existing interface increase commensurately. Hypothetical southeastward (downstream) re-positioning of the existing G-54 salinity-control structure may prevent the interface from moving northwestward along and near the North New River canal, but beneficial effects are localized. Implementation of freshwater recharge wells in the city of Hallandale Beach may also have only a localized freshening effect in the aquifer and little appreciable effect on the freshwater-saltwater interface or on concentrations of salinity at well fields. Model accuracy and use are limited by uncertainty in the physical properties and boundary conditions of the system, uncertainty in historical and future conditions, and generalizations made in the mathematical relationships used to describe the physical processes of groundwater flow and transport. Because of these limitations, model results should be considered in relative rather than absolute terms. Nonetheless, model results do provide useful information on the relative scale of response of the system to changes in pumping distribution, sea-level rise, and mitigation activities.

ABSTRACT:

In 2010, the U.S. Geological Survey, in cooperation with the San Antonio Water System, began a study to assess the brackish-water movement within the Edwards aquifer (more specifically the potential for brackish-water encroachment into wells near the interface between the freshwater and brackish-water transition zones, referred to in this report as the transition-zone interface) and effects on spring discharge at Comal and San Marcos Springs under drought conditions using a numerical model. The quantitative targets of this study are to predict the effects of higher-than-average groundwater withdrawals from wells and drought-of-record rainfall conditions of 1950-56 on (1) dissolved-solids concentration changes at production wells near the transition-zone interface, (2) total spring discharge at Comal and San Marcos Springs, and (3) the groundwater head (head) at Bexar County index well J-17. The predictions of interest, and the parameters implemented into the model, were evaluated to quantify their uncertainty so the results of the predictions could be presented in terms of a 95-percent credible interval. The model area covers the San Antonio and Barton Springs segments of the Edwards aquifer; the history-matching effort was focused on the San Antonio segment. A previously developed diffuse-flow model of the Edwards aquifer, which forms the basis for the model in this assessment, is primarily based on a conceptualization in which flow in the aquifer is predominately through a network of numerous small fractures and openings. Primary updates to this model include an extension of the active area downdip, a conversion to an 8-layer SEAWAT variable-density flow and transport model to simulate dissolved-solids concentration effects on water density, history matching to 1999-2009 conditions, and parameter estimation in a highly parameterized context using automated methods in PEST (a model-independent Parameter ESTimation code). In addition to the best-fit parameter values derived from history matching, the uncertainty of model parameters was also estimated by using linear uncertainty analysis. Comparison of prior (before history matching) and posterior (after history matching) variances of parameters indicate that the information within the observation dataset used for history matching informs many parameters. The concentration threshold parameters were well-informed by the observation dataset as their posterior distributions were much narrower than their prior distributions. The transition-zone scaling parameters of hydraulic conductivity, effective porosity, and specific storage were all informed by the observation dataset, as evidenced by the difference between the prior and posterior variances. Saline-zone scaling parameters, alternatively, were not informed by the observation dataset for effective porosity and specific storage. Resulting posterior drier-month, wetter-month, and annual recharge multiplier parameter variances are important to understanding how well recharge is estimated and implemented within the model. The shifts of the posterior distributions left and right indicate that there were zones where less or more water was needed in the model. The widths of the distributions were not decreased substantially, indicating that many of the best-fit recharge parameters are not statistically different from the initial values specified in the history-matching effort. Recharge from rainfall is the driving force behind groundwater flow and heads in the aquifer; therefore, an increase in understanding of this process would benefit model development by potentially decreasing the uncertainty of this parameter. The history-matching effort was most helpful in informing the parameters in the model that control discharge at springs, namely, the spring orifice (drain) altitude and drain conductance parameters for each spring. The uncertainty assessment of the predictive model (a hypothetical recurrence of 1950-56 drought conditions and higher-than-average groundwater withdrawals from wells) provided insights into the potential effects of these conditions on dissolved-solids concentration changes at production wells near the transition-zone interface, discharges at Comal and San Marcos Springs, and heads at Bexar County index well J-17. Results at the 25 production wells near the transition-zone interface indicate that the uncertainty of model input parameters based on expert knowledge yielded an upper bound of the 95-percent credible interval of dissolved-solids concentrations that exceeds the secondary drinking water standards of 1,000 milligrams per liter (mg/L) of the Texas Commission on Environmental Quality (TCEQ) for many wells. However, the history-matching process provided key information to inform prediction-sensitive model parameters and therefore, contributed to a substantial decrease of the upper bound of the 95-percent credible interval to below the secondary drinking water standards. Reductions in dissolved-solids concentration changes were on the order of 400 mg/L to 1,300 mg/L. The reduction in uncertainty in regards to this prediction implies that this prediction of dissolved-solids concentration change can be made with some certainty using this current model and that those parameters that control this prediction are informed by the observation dataset. Even though predictive uncertainty was reduced for this prediction, dissolved-solids concentration changes were still greater than zero, indicating a minimal increase in concentration at these 25 production wells during the 7-year simulation period is likely. However, this minimal concentration increase indicates a small potential for movement of the brackish-water transition zone near these wells during the 7-year simulation period of drought-ofrecord (1950-56) rainfall conditions with higher-than-average groundwater withdrawals by wells. Predictive results of total spring discharge during the 7-year period, as well as head predictions at Bexar County index well J-17, were much different than the dissolved-solids concentration change results at the production wells. These upper bounds are an order of magnitude larger than the actual prediction which implies that (1) the predictions of total spring discharge at Comal and San Marcos Springs and head at Bexar County index well J-17 made with this model are not reliable, and (2) parameters that control these predictions are not informed well by the observation dataset during historymatching, even though the history-matching process yielded parameters to reproduce spring discharges and heads at these locations during the history-matching period. Furthermore, because spring discharges at these two springs and heads at Bexar County index well J-17 represent more of a cumulative effect of upstream conditions over a larger distance (and longer time), many more parameters (with their own uncertainties) are potentially controlling these predictions than the prediction of dissolved-solids concentration change at the prediction wells, and therefore contributing to a large posterior uncertainty.

ABSTRACT:

Groundwater has been a part of the city of Santa Barbara's water-supply portfolio since the 1800s; however, since the 1960s, the majority of the city's water has come from local surface water, and the remainder has come from groundwater, State Water Project, recycled water, increased water conservation, and as needed, seawater desalination. Although groundwater from the Santa Barbara and Foothill groundwater basins only accounts for a small percentage of the long-term supply, it is an important source of supplemental water during times of surface-water shortages. During the late 1980s and early 1990s, production wells extracted additional groundwater to compensate for drought related water-delivery shortfalls from other sources; in response, water levels declined substantially in the Santa Barbara and Foothill groundwater basins (below sea level in the Santa Barbara groundwater basin). In coastal basins that have groundwater extraction near shore, seawater intrusion is often a problem. Seawater intrusion in the Santa Barbara groundwater basin is thought to be more limited than in other coastal basins because of an offshore fault that acts as a partial barrier to groundwater flow. During the late 1980s and early 1990s, seawater intrusion was observed in the Santa Barbara groundwater basin, as indicated by increased chloride concentrations at several monitoring wells that ranged from 200 ft to 1,300 ft from the ocean and as close as 2,900 ft to the nearest pumping well. This demonstrated that seawater can intrude into the Santa Barbara groundwater basin when groundwater levels fall below sea level near the coast. The city of Santa Barbara is interested in developing a better understanding of the sustainability of its groundwater supplies. In 2014, California adopted historic legislation to manage its groundwater: the Sustainable Groundwater Management Act (SGMA). The SGMA requires the development and implementation of Groundwater Sustainability Plans in 127 priority groundwater basins; although Santa Barbara was not a designated priority basin, the city is taking steps to achieve sustainability. Sustainability was defined in the SGMA in terms of avoiding undesirable results: significant and unreasonable groundwater-level declines, reduction in groundwater storage, seawater intrusion, water-quality degradation, land subsidence, and surface-water depletion. In this project, a cooperative study between the U.S. Geological Survey (USGS) and the city of Santa Barbara, sustainable yield is defined as the volume of groundwater that can be pumped from storage without causing water-level drawdowns and the associated increases in seawater intrusion (as indicated by increases in measured chloride concentrations) at selected wells. In order to estimate the sustainability of Santa Barbara's groundwater basins, a three-dimensional density-dependent groundwater-flow and solute-transport model (the Santa Barbara Flow and Transport Model, or SBFTM) was developed on the basis of an existing groundwater-flow model. To simulate seawater intrusion to the Santa Barbara Basin under various management strategies, the SBFTM uses the USGS code SEAWAT to simulate salinity transport and variable-density flow. The completed SBFTM was coupled with a management optimization tool, in this case a multi-objective evolutionary algorithm, to determine optimal pumping strategies that maximize the sustainable yield and at the same time satisfy user-defined drawdown and chloride-concentration constraints. As part of this study, a three-dimensional hydrogeologic framework model was developed to quantify the extent and hydrogeologic characteristics of the Santa Barbara and Foothill groundwater basins and to help define the discretization and hydraulic properties used in the SBFTM. The development of the hydrogeologic framework model required the collection and reconciliation of geologic and geophysical data from existing maps, reports, and databases, along with geologic and hydrologic data from recently drilled wells. These data were integrated into a three-dimensional hydrogeologic framework model that defines the stratigraphy and geometry of the aquifer zones and the major geologic structures in the basin. The hydrogeologic framework model also quantifies the variation in sediment grain size within each aquifer zone as the percentage of coarse-grained sediment. Previous studies indicated that there are two principal water-producing zones in the Santa Barbara groundwater basin, the upper and lower producing zones; an additional thin, productive zone was identified as part of this study. This middle producing zone is not as areally extensive as the upper and lower producing zones and only exists in the coastal part of Storage Unit I. These producing zones are bounded at depth by less productive shallow, middle, and deep zones. Two versions of the SBFTM were constructed: an initial-condition model and a modern transient model. The initial-condition model is a long-term transient model that simulates flow and solute-transport conditions during a period with limited anthropogenic influences preceeding the modern transient model. The simulation-transient model simulates flow and transport conditions from 1929 through 2013; however, because of data availability, the focus of the model calibration was 1972-2013. The SBFTM was calibrated to measured groundwater levels and drawdown, as well as measured chloride concentrations and change in concentrations, using a combination of automated and trial-and-error parameter-estimation techniques. A sensitivity analysis indicated that, in general, the SBFTM was most sensitive to recharge- and pumping-distribution parameters, specifically those controlling the amount of small-catchment recharge and the distribution of water extraction by hydrogeologic layer for production wells. The model was also sensitive to parameters controlling stream-recharge rates, horizontal and vertical hydraulic conductivity, and porosity. From 1929 to 1971, most of the water entering the area represented by the SBFTM was from creek and small-catchment recharge, and the majority of water leaving the SBFTM area was from pumping, discharge to creeks, and drains. In addition, about 37 percent of the total pumpage came from a net reduction in groundwater storage. From 1972 to 2013, the amount of water entering and leaving the SBFTM was fairly similar as that from 1929 to 1971, except the reduction in pumpage added about 17,000 acre-ft of water to storage. During this later period, there were also times of storage loss. For example, during July 1990, a month when approximately 705 acre-ft of groundwater was pumped in the study area, the pumpage was much greater than all sources of recharge combined, and about 382 acre-ft of water was removed from groundwater storage. Simulated hydraulic heads replicated the observed data to an acceptable matching of the measured water-level, flow direction, and vertical gradients. Simulated hydrographs for selected wells were in good agreement with the measured data, with an average residual of -2.7 ft and a standard deviation of 14.5 ft, indicating that the simulated heads, on average, underestimated the observed water levels. An examination of the model fit indicated that most of the discrepancies were lower simulated heads at wells proximal to production well sites. The simulated chloride concentrations reasonably matched the rising limbs of the measured breakthrough curves in terms of timing and magnitude; however, the simulation overestimated the chloride concentrations on the falling limbs. The overestimation of low chloride concentrations was attributed to the model overestimating the advance of the chloride front during periods of heavy pumping and underestimating the retreat of the chloride front during periods of low pumping. These simulation errors would result in a conservative response by local water managers to seawater intrusion. The SBFTM was used to develop a collection of predictive simulations optimized to produce pumping schedules that maximize yield, subject to a set of constraints and competing objectives. The simulations were grouped as scenarios that differed in their time horizon, initial conditions for groundwater levels and chloride concentrations, as well as precipitation, which was incorporated into the model through simulated recharge. Overall, five scenarios were developed in a multi-objective framework to obtain optimal pumping rates for all of the wells managed by the city, while minimizing excessive drawdown and seawater intrusion. For the current study, complexities in the simulation model and the optimization formulation required additional considerations. Incorporating the solute-transport equations to simulate chloride transport added a highly nonlinear process that is solved iteratively in each time step of the groundwater-flow model. These nonlinearities, coupled with the highly refined grid in the current model, creates challenges for many traditional optimization methods. Therefore, an optimization method was needed that could address nonlinear relationships as well as a very large problem size. Lastly, the optimization problem was reformulated to include multiple objectives without requiring convergence to a single solution. This approach, guided by the city's objectives, allowed the maximum extraction of information from the complex simulation. Borg, a multi-objective evolutionary algorithm, was chosen as the optimization algorithm for this study for several reasons: (1) it is very computationally efficient; (2) it can run in parallel; (3) it requires little user input; and (4) it can solve for multiple competing objectives. The first three points allow the algorithm to proceed toward the optimal solutions at the fastest possible rate. The fourth point is advantageous for large, complex optimization problems because it is difficult to formulate the optimization problem in a way that produces only one optimal solution. The problem formulation consisted of four competing objectives and a constraint set in accordance with the main concerns of the city. The objectives were maximizing total pumpage, minimizing seawater intrusion, minimizing total drawdown in production wells, and minimizing the maximum drawdown. The constraints were pump capacity, meeting drinking-water standards for chloride, maintaining a specified minimum flowrate to a groundwater treatment plant, and maintaining minimum water levels in pumping wells. The decision variables either were quarterly pumpage by well or total pumpage by basin. Five optimization scenarios were developed that allow the decision makers to evaluate a range of optimal solutions for a variety of water levels and chloride concentrations as well as potential future climatic conditions. Three scenarios (1, 2, and 5) were multi-objective optimization formulations that allowed for variations in management preferences and climatic conditions. The other two scenarios (3 and 4) were designed to examine the optimization results to answer specific questions. Scenario 1 described the best-case sustainable yield assuming a full basin (that is, high initial water levels) and typical climate conditions for 10 years. Scenario 2 also started with a full basin; however, this was followed by a 10-year drought. Scenario 3 determined if an empty basin (that is, low initial water levels) would recover to full conditions (1998 conditions) given climate assumptions and optimal pumping schedules from scenarios 1 and 2. Scenario 4 was designed to produce decision rules that can be used by water managers to help choose an optimal pumping schedule based on measured water-level or chloride data. Scenario 5 identified future pumping schedules based on short-term climate variations during a 2-year management horizon. The results from scenarios 1 and 2 described the differences in maximum pumpage in the basin under typical and dry long-term climate projections, respectively. The scenario 1 results indicated the maximum 10-year pumpage of the basin was about 31,300 acre-ft under typical conditions and controlling simulated seawater intrusion and drawdowns. For scenario 2, less recharge over the 10-year dry climate produced a maximum pumpage estimate of 30,000 acre-ft to control seawater intrusion and drawdowns. The larger pumpage for scenario 1 resulted in more seawater intrusion, but less total drawdown, compared to that of scenario 2. Results for scenarios 3 and 4 showed the basin's response to management actions combined with climate projections. Both scenarios used the optimal pumping schedules and the 10-year climates from scenarios 1 and 2. The scenario 3 results showed that under minimal pumping, the basin did not fully recover to 1998 water levels within 10 years under either climate scenario. The relatively larger recharge from the typical climate resulted in less drawdown at coastal monitoring wells after the 10-year recovery period than that from the dry climate. The location of the seawater intrusion front was not appreciably different between the scenarios, however. Scenario 4 used the optimal results from scenarios 1 and 2 to produce decision-rule curves that illustrated the pumpage for each basin, given measured levels of chloride concentration or drawdown. This allowed the use of additional measurements at monitoring wells to assess future management decisions on the basis of the sensitivity of observations of drawdown and seawater intrusion to various pumping rates. Scenario 5 allowed managers to investigate the effects of short-term climate variations on optimal pumping schedules. Three specific 2-year simulations were optimized: typical-to-dry (scenario 5A), dry-to-typical (scenario 5B), and dry-to-dry (scenario 5C). The most noteable result from scenario 5 was the overall reduction in optimal pumpage for most schedules in scenario 5C, when the climate is simulated as dry-to-dry. There are also many optimal pumping schedules that produced an overall increase in waterlevels over the two-year simulation period, regardless of climatic condition. Similar to scenario 2, the scenario 5C results represents conservative yield estimates under a minimal-precipitation climatic condition.

ABSTRACT:

Arkansas continues to be one of the largest users of groundwater in the Nation. As such, long-term planning and management are essential to ensure continued availability of groundwater and surface water for years to come. The Mississippi Embayment Regional Aquifer Study (MERAS) model was developed previously as a tool to evaluate groundwater availability within the Mississippi embayment, which encompasses much of eastern Arkansas where the majority of groundwater is used. The Arkansas Water Plan is being updated for the first time since 1990 and serves as the State's primary, comprehensive water-resources planning and guidance document. The MERAS model was selected as the best available tool for evaluation of specific water-use pumping scenarios that are currently being considered by the State of Arkansas. The model, developed as part of the U.S. Geological Survey Groundwater Resources Program's assessment of the Nation's groundwater availability, is proving to be invaluable to the State as it works toward development of a sustained yield pumping strategy. One aspect of this investigation was to evaluate multiple methods to improve the match of observed to simulated groundwater levels within the Mississippi River Valley alluvial and middle Claiborne (Sparta) aquifers in the MERAS model. Five primary methods were evaluated: (1) explicit simulation of evapotranspiration (ET), (2) upgrade of the Multi-Node Well (MNW2) Package, (3) geometry improvement within the Streamflow Routing (SFR) Package, (4) parameter estimation of select aquifer properties with pilot points, and (5) modification of water-use estimates. For the planning purposes of the Arkansas Water Plan, three scenarios were developed to evaluate potential future conditions: (1) simulation of previously optimized pumping values within the Mississippi River Valley alluvial and the middle Claiborne aquifers, (2) simulated prolonged effects of pumping at average recent (2000-5) rates, and (3) simulation of drawdown constraints on most pumping wells. The explicit simulation of ET indicated little, if any, improvement of model fit at the expense of much longer simulation time and was not included in further simulations. Numerous attempts to fully utilize the MNW2 Package were unsuccessful in achieving model stability, though modifications made to the water-use dataset remained intact. Final improvements in the residual statistics may be attributed to a single method, or a cumulative effect of all other methods (geometry improvement with the SFR Package, parameter estimation with pilot points, and modification of water-use estimates) attempted. The root mean squared error (RMSE) for all observations in the model is 22.65 feet (ft) over a range in observed hydraulic head of 741.66 ft. The RMSE for water-level observations in the Mississippi River Valley alluvial aquifer is 14.14 ft (an improvement of almost 3 ft) over a range in observed hydraulic head of 297.25 ft. The RMSE for the Sparta aquifer is 32.02 ft (an improvement of approximately 3 ft) over a range in observed hydraulic head of 634.94 ft. Three scenarios were developed to utilize a steady-state version of the MERAS model. Scenario 1 was developed to use pumping values resulting from the optimization of baseline rates (typically 1997 pumping rates) from previous optimization modeling of the alluvial aquifer and the Sparta aquifer. Scenario 2 was developed to evaluate the prolonged effects of pumping from the alluvial aquifer at recent pumping rates. Scenario 3A was designed to evaluate withdrawal limits from the alluvial aquifer by utilizing drawdown constraints equal to an altitude of approximately 50 percent of the predevelopment saturated thickness of the alluvial aquifer or 30 ft above the bottom of the alluvial aquifer, whichever was greater. The results of scenario 1 indicate large water-level declines throughout the area of the alluvial aquifer, regardless of the substitution of the optimized pumping values from earlier model simulations. The results of scenario 2 also indicate large areas of water-level decline, as compared to half of the saturated thickness, throughout the alluvial aquifer. The results of scenario 3A reveal some effects from the inclusion of multiple aquifers in a single simulation. The initial configuration of scenario 3A resulted in water levels well below the defined drawdown constraint, and some areas of depleted aquifer (water levels that are near or below the bottom of the aquifer) in east-central Arkansas. A fourth simulation (scenario 3B) was configured to apply the same drawdown constraints from the alluvial aquifer wells to the Sparta aquifer wells in the depleted area. These drawdown constraints reduce leakage from the alluvial aquifer to the underlying Sparta aquifer. This configuration did not produce depleted areas within the alluvial aquifer. Scenarios 3A and 3B indicate that even when pumping is limited in the alluvial aquifer, water levels in the alluvial aquifer may continue to decline in some areas because of pumping in the underlying Sparta aquifer.

ABSTRACT:

In cooperation with the Harris-Galveston Subsidence District, Fort Bend Subsidence District, and Lone Star Groundwater Conservation District, the U.S. Geological Survey developed and calibrated the Houston Area Groundwater Model (HAGM), which simulates groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system in Texas from predevelopment (before 1891) through 2009. Withdrawal of groundwater since development of the aquifer system has resulted in potentiometric surface (hydraulic head, or head) declines in the Gulf Coast aquifer system and land-surface subsidence (primarily in the Houston area) from depressurization and compaction of clay layers interbedded in the aquifer sediments. The MODFLOW-2000 groundwater flow model described in this report comprises four layers, one for each of the hydrogeologic units of the aquifer system except the Catahoula confining system, the assumed no-flow base of the system. The HAGM is composed of 137 rows and 245 columns of 1-square-mile grid cells with lateral no-flow boundaries at the extent of each hydrogeologic unit to the northwest, at groundwater divides associated with large rivers to the southwest and northeast, and at the downdip limit of freshwater to the southeast. The model was calibrated within the specified criteria by using trial-and-error adjustment of selected model-input data in a series of transient simulations until the model output (potentiometric surfaces, land-surface subsidence, and selected water-budget components) acceptably reproduced field measured (or estimated) aquifer responses including water level and subsidence. The HAGM-simulated subsidence generally compared well to 26 Predictions Relating Effective Stress to Subsidence (PRESS) models in Harris, Galveston, and Fort Bend Counties. Simulated HAGM results indicate that as much as 10 feet (ft) of subsidence has occurred in southeastern Harris County. Measured subsidence and model results indicate that a larger geographic area encompassing this area of maximum subsidence and much of central to southeastern Harris County has subsided at least 6 ft. For the western part of the study area, the HAGM simulated as much as 3 ft of subsidence in Wharton, Jackson, and Matagorda Counties. For the eastern part of the study area, the HAGM simulated as much as 3 ft of subsidence at the boundary of Hardin and Jasper Counties. Additionally, in the southeastern part of the study area in Orange County, the HAGM simulated as much as 3 ft of subsidence. Measured subsidence for these areas in the western and eastern parts of the HAGM has not been documented.

ABSTRACT:

Malioboro is a famous tourism area in Yogyakarta City, in which there are many hotels and increases every years and this follows by the increasing needs of fresh water taken from underlying groundwater. The decreasing of groundwater table become a great issue on this area, therefore the objective of the research is to predict groundwater table change in the next 10 years due to increase abstraction of groundwater. To answer the mentioned objectives, field observation of dug wells and collection of secondary data of log bores also calculation of recharge and water abstraction are used to understand and build the conceptual model of local groundwater system. The prediction is done by conducting simulation on a numerical groundwater model by using MODFLOW. The local groundwater system consists of two aquifer layers; upper aquifer and lower aquifer which separated incompletely by clay layer. Simulation is conducting by distributing the groundwater pumping for domestic and non-domestic utilization by dug wells in the upper aquifer, whereas deep wells non-domestic utilization are applied only in the lower aquifer. Simulations are conducted twice for the recent day and the next ten years prediction of groundwater abstraction. In the case of groundwater abstraction in the next ten years, dug wells abstraction and deep wells pumping are setting to 4727 m3/day and 1648 m3/day, respectively. The groundwater pumping rates is representing increase of groundwater withdrawal of users in the range only between 0.2-1.2 % per year compare to the recent condition. The simulation reveals change occur on groundwater table depth and pattern. In average, the groundwater table will decrease of about 0.25 meter.

ABSTRACT:

A study was undertaken to understand the groundwater flow conditions in the Bangkok Basin, Thailand, by comparing 14 C-based and simulated groundwater ages. 14 C measurements were made on about 50 water samples taken from wells throughout the basin. Simulated ages were obtained using 1) backward-pathline tracking based on the well locations, and 2) results from a three-dimensional groundwater flow model. Comparisons of ages at these locations reveal a large difference between 14 C-based ages and ages predicted by the steady-state groundwater flow model. Mainly, 14 C and 13C analyzes indicate that groundwater in the Bangkok area is about 20,000 years old, whereas steady-state flow and transport simulations imply that groundwater in the Bangkok area is 50,000-100,000 years old. One potential reason for the discrepancy between simulated and 14C-based ages is the assumption in the model of steady-state flow. Groundwater velocities were probably greater in the region before about 10,000 years ago, during the last glacial maximum, because of the lower position of sea level and the absence of the surficial Bangkok Clay. Paleoflow conditions were estimated and then incorporated into a second set of simulations. The new assumption was that current steady-state flow conditions existed for the last 8,000 years but were preceded by steady-state conditions representative of flow during the last glacial maximum. This transient paleohydrologic simulation yielded a mean simulated age that more closely agrees with the mean 14 C-based age, especially if the 14C-based age corrected for diffusion into clay layers. Although the uncertainties in both the simulated and 14 C-based ages are nontrivial, the magnitude of the improved match in the mean age using a paleohydrologic simulation instead of a steady-state simulation suggests that flow conditions in the basin have changed significantly over the last 10,000-20,000 years. Given that the valid age range of 14 C-dating methods and the timing of the last glacial maximum are of similar magnitude, adjustments for paleohydrologic conditions may be required for many such studies.

ABSTRACT:

Watersheds of three streams, the Mousam River, Branch Brook, and Merriland River in southeastern Maine were investigated from 2010 through 2013 under a cooperative project between the U.S. Geological Survey and the Maine Geological Survey. The Branch Brook watershed previously had been deemed at risk by the Maine Geological Survey because of the proportionally large water withdrawals compared to estimates of the in-stream flow requirements for habitat protection. The primary groundwater withdrawals in the study area include a water-supply well in the headwaters of the system and three water-supply wells in the coastal plain near the downstream end of the system. A steady-state groundwater flow model was used to understand the movement of water within the system, to evaluate the water budget and the effect of groundwater withdrawals on streamflows, and to understand streamflow depletion in relation to the State of Maine's requirements to maintain in-stream flows for habitat protection. Delineation of the simulated groundwater divides compared to the surface-water divides suggests that the groundwater divides in the headwater areas do not exactly correspond to the surface-water divides. Under both pumping and non-pumping conditions, groundwater flows from the headwaters of the Branch Brook watershed into the Mousam River watershed. Pumping in the Mousam River watershed captures a small amount of groundwater from the Branch Brook basin. The cumulative effect of groundwater withdrawals on base flows in two rivers in the study area (Branch Brook and the Merriland River) was evaluated using the groundwater flow model. Streamflow depletion in the headwaters of Branch Brook was 0.12 cubic feet per second (ft3/s) for the steady-state simulation, or about 10 percent of the average base flow at that location. Downstream on Branch Brook, the total streamflow depletion from all the wells was 0.59 ft3/s, or 3 percent of the average base flow at that location. In the Merriland River downstream from the Merriland River well, the total amount of streamflow depletion was 0.6 ft3/s, or about 7 percent of the average base flow. The groundwater model was used to evaluate several different scenarios that could affect streamflow and groundwater discharging to the rivers and streams in the study area. The scenarios were (1) no pumping from the water-supply wells; (2) current pumping from the water-supply wells, but simulated drought conditions (25 percent reduction in recharge); (3) current recharge, but with increased pumping from the large water-supply wells; and (4) drought conditions and increased pumping combined. Simulations of increased pumping in the water-supply wells resulted in streamflow depletion in the headwaters of Branch Brook increasing to 16 percent of the headwater base flow. Simulated increases in the pumping in the coastal plain wells increased the amount of streamflow depletion to 6 percent of the flow in Branch Brook and to 8 percent of the flow in the Merriland River. The additional stress of a drought imposed on the model (25 percent less recharge) had a substantial impact on streamflows, as expected. If the simulated drought occurred simultaneously with an increase in pumping, the base flows would be reduced 48 percent in the headwaters of Branch Brook, compared to the no-pumping scenario. Downstream in Branch Brook, the total reduction in flow would be 29 percent of the simulated base flows in the no-pumping scenario, and in the Merriland River, the reduction would be 33 percent of the base flows in the no-pumping scenario. The study evaluated two different methods of calculating in-stream flow requirements for Branch Brook and the Merriland Rivera set of statewide equations used to calculate monthly median flows and the MOVE.1 record-extension technique used on site-specific streamflow measurements. The August median in-stream flow requirement in the Merriland River was calculated as 7.18 ft3/s using the statewide equations but was 3.07 ft3/s using the MOVE.1 analysis. In Branch Brook, the August median in-stream flow requirements were calculated as 20.3 ft3/s using the statewide equations and 11.8 ft3/s using the MOVE.1 analysis. In each case, using site-specific data yields an estimate of in-stream flow that is much lower than an estimate the statewide equations provide.

ABSTRACT:

Increasing population, agricultural development (including shifts to more water-intensive crops), and climate variability are placing increasingly larger demands on available groundwater resources in the Pajaro Valley, one of the most productive agricultural regions in the world. This study provided a refined conceptual model, geohydrologic framework, and integrated hydrologic model of the Pajaro Valley. The goal of this study was to produce a model capable of being accurate at scales relevant to water management decisions that are being considered in the revision and updates to the Basin Management Plan (BMP). The Pajaro Valley Hydrologic Model (PVHM) was designed to reproduce the most important natural and human components of the hydrologic system and related climatic factors, permitting an accurate assessment of groundwater conditions and processes that can inform the new BMP and help to improve planning for long-term sustainability of water resources. Model development included a revision of the conceptual model of the flow system, reevaluation of the previous model transformed into MODFLOW, implementation of the new geohydrologic model and conceptual model, and calibration of the transient hydrologic model. The PVHM model, using MODFLOW with the Farm Process (MF-FMP2), is capable of being accurate at seasonal to interannual time frames and subregional to valley-wide spatial scales for the assessment of the groundwater hydrologic budget for water years 1964-2009, as well as potential assessment of the BMP components and sustainability analysis of conjunctive use. The model provides a good representation of the regional flow system and the use and movement of water throughout the valley. Simulated changes in storage over time show that, prior to the 1984-92 dry period, significant withdrawals from storage occurred only during drought years. Since about 1993, growers in the Pajaro Valley have shifted to more water intensive crops, such as strawberries, bushberries, and vegetable row crops, as well as making additional rotational plantings, which have increased demand on limited groundwater resources. Simulated groundwater flow indicates that vertical hydraulic gradients between horizontal layers fluctuate and even reverse in several parts of the basin as recharge and pumpage rates change seasonally and annually. The majority of recharge predominantly enters the Alluvial aquifer system, and along with pumpage and the largest fractions of storage depletion, occurs in the inland regions. Coastal inflow as seawater intrusion replaces much of the potential storage depletion in the coastal regions. The simulated long-term imbalance between inflows and outflows indicates overdraft of the groundwater basin averaging about 12,950 acre-feet per year (acre-ft/yr) over the 46-year period of water years (1964-2009). Annual overdraft varies considerably from year to year, depending on land use, pumpage, and climate conditions. Climatically driven factors can affect inflows, outflows, and water use by as much as a factor of two between wet and dry years. Coastal inflows and outflows vary by year and by aquifer; the net coastal inflow, or seawater intrusion, ranges from about 1,000 to more than 6,000 acre-ft/yr. Maps of simulated and measured water-level elevations indicate regions with water levels below sea level in the alluvium and Aromas layers. Ongoing expansion of local hydrologic monitoring networks indicates the importance of these networks to the understanding of changes in groundwater flow, streamflow, and streamflow infiltration. In particular, the monitoring of streamflow, groundwater pumpage, and groundwater levels throughout the valley not only indicates the state of the resources, but also provides valuable information for model calibration and for model-based evaluation of management actions. The HS-ASR was simulated for the years 2002-09, and replaced about about 1,290 acre-ft of coastal pumpage. This was combined with the simulation of additional 6,200 acre-ft of deliveries from supplemental wells, recycled water, and city connection deliveries through the CDS that also supplanted some coastal pumpage. Total simulated deliveries were 7,350 acre-ft of the 7,500 acre-ft of reported deliveries for the period 2002-09. The completed CDS should be capable of delivering about 8.8 million cubic meters (7,150 acre-ft) of water per year to coastal farms within the Pajaro Valley, if all the local supply components were fully available for this purpose. This would represent about 15 percent of the 48,300 acre-ft (59.6 million cubic meters) average agricultural pumpage for the period 2005 to 2009. Combined with the potential capture and reuse of some of the return flows and tile-drain flows, this could represent an almost 70 percent reduction of average overdraft for the entire valley and a large part of the coastal pumpage that induces seawater intrusion.

ABSTRACT:

Water managers in the Santa Rosa Plain face the challenge of meeting increasing water demand with a combination of Russian River water, which has uncertainties in its future availability; local groundwater resources; and ongoing and expanding recycled water and water from other conservation programs. To address this challenge, the U.S. Geological Survey, in cooperation with the Sonoma County Water Agency, the cities of Cotati, Rohnert Park, Santa Rosa, and Sebastopol, the town of Windsor, the California American Water Company, and the County of Sonoma, undertook development of a fully coupled groundwater and surface-water model to better understand and to help manage the hydrologic resources in the Santa Rosa Plain watershed. The purpose of this report is to (1) describe the construction and calibration of the fully coupled groundwater and surface-water flow model for the Santa Rosa Plain watershed, referred to as the Santa Rosa Plain hydrologic model; (2) present results from simulation of the Santa Rosa Plain hydrologic model, including water budgets, recharge distributions, streamflow, and the effect of pumping on water-budget components; and (3) present the results from using the model to evaluate the potential hydrologic effects of climate change and variability without pumpage for water years 2011-99 and with projected pumpage for water years 2011-40.

ABSTRACT:

The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and public supply uses in the Pecos County region of western Texas. The U.S. Geological Survey completed a comprehensive, integrated analysis of available hydrogeologic data to develop a numerical groundwater-flow model of the Edwards-Trinity and related aquifers in the study area in parts of Brewster, Jeff Davis, Pecos, and Reeves Counties. The active model area covers about 3,400 square miles of the Pecos County region of Texas west of the Pecos River, and its boundaries were defined to include the saturated areas of the Edwards-Trinity aquifer. The model is a five-layer representation of the Pecos Valley, Edwards-Trinity, Dockum, and Rustler aquifers. The Pecos Valley aquifer is referred to as the alluvial layer, and the Edwards-Trinity aquifer is divided into layers representing the Edwards part of the Edwards-Trinity aquifer and the Trinity part of the Edwards-Trinity aquifer, respectively. The calibration period of the simulation extends from 1940 to 2010. Simulated hydraulic heads generally were in good agreement with observed values; 1,684 out of 2,860 (59 percent) of the simulated values were within 25 feet of the observed value. The average root mean square error value of hydraulic head for the Edwards-Trinity aquifer was 34.2 feet, which was approximately 4 percent of the average total observed change in groundwater-level altitude (groundwater level). Simulated spring flow representing Comanche Springs exhibits a pattern similar to observed spring flow. Independent geochemical modeling corroborates results of simulated groundwater flow that indicates groundwater in the Edwards-Trinity aquifer in the Leon-Belding and Fort Stockton areas is a mixture of recharge from the Barilla and Davis Mountains and groundwater that has upwelled from the Rustler aquifer. The model was used to simulate groundwater-level altitudes resulting from prolonged pumping to evaluate sustainability of current and projected water-use demands. Each of three scenarios utilized a continuation of the calibrated model. Scenario 1 extended recent (2008) irrigation and nonirrigation pumping values for a 30-year period from 2010 to 2040. Projected groundwater-level changes in and around the Fort Stockton area under scenario 1 change little from current conditions, indicating that the groundwater system is near equilibrium with respect to recent (2008) pumping stress. Projected groundwater-level declines in the eastern part of the model area ranging from 5.0 to 15.0 feet are likely the result of nonequilibrium conditions associated with recent increases in pumping after a prolonged water-level recovery period of little or no pumping. Projected groundwater-level declines (from 15.0 to 31.0 feet) occurred in localized areas by the end of scenario 1 in the Leon-Belding area. Scenario 2 evaluated the effects of extended recent (2008) pumping rates as assigned in scenario 1 with year-round maximum permitted pumping rates in the Belding area. Results of scenario 2 are similar in water-level decline and extent as those of scenario 1. The extent of the projected groundwater-level decline in the range from 5.0 to 15.0 feet in the Leon-Belding irrigation area expanded slightly (about a 2-percent increase) from that of scenario 1. Maximum projected groundwater-level declines in the Leon-Belding irrigation area were approximately 31.3 feet in small isolated areas. Scenario 3 evaluated the effects of periodic increases in pumping rates over the 30-year extended period. Results of scenario 3 are similar to those of scenario 2 in terms of the areas of groundwater-level decline; however, the maximum projected groundwater-level decline increased to approximately 34.5 feet in the Leon-Belding area, and the extent of the decline was larger in area (about a 17-percent increase) than that of scenario 2. Additionally, the area of projected groundwater-level declines in the eastern part of the model area increased from that of scenario 2 two individual areas of decline coalesced into one larger area. The localized nature of the projected groundwater-level declines is a reflection of the high degree of fractured control on storage and hydraulic conductivity in the Edwards-Trinity aquifer. Additionally, the finding that simulated spring flow is highly dependent on the transient nature of hydraulic heads in the underlying aquifer indicates the importance of adequately understanding and characterizing the entire groundwater system.

ABSTRACT:

Water resources sustainable management is a vital issue for small islands where groundwater is often the only available water resource. Nauru is an isolated and uplifted limestone atoll island located in the Pacific Ocean. Politecnico di Milano performed a feasibility study for the development of sustainable use of groundwater on the island. This paper focuses on the first phase of the study that concerns the conceptual site model development, the hydrogeological characterization and the 2D model implementation. During the project, different activities were performed such as GNSS topographic survey of monitoring wells and groundwater level surveys taking into account tidal fluctuation. This data collection and the analysis of previous studies made it possible to identify the most suitable areas for groundwater sustainable extraction. The characterization findings suggested, unlike previous studies and surveys, the presence of only few drought resilient thin freshwater lenses, taking place in low conductivity sandy deposits, unexpectedly next to the seashore. Thanks to the 2D modeling results, it has been possible to clarify the mechanism that allows the storage of freshwater so close to the sea.

ABSTRACT:

A multicell groundwater model was constructed to investigate the potential improvement in the modelling of karstic aquifers by using a mixed equation suitable for both the free surface and pressure flow conditions in karstic conduits. To estimate the model parameters the shuffled complex evolution (SCE) optimisation method was used. This ensured a fast and objective model calibration. The model was applied to two real-world karstic aquifers and it became clear that in case of absence of water level measurements, the use of the mixed equation did not improved the performance. In cases where both spring discharge and water level measurements were available, the use of the mixed equation proved to be advantageous in reproducing the features of the observed time series especially of the water level. (c) 2005 Elsevier B.V. All rights reserved.

ABSTRACT:

The Miocene Columbia River Basalt Group and younger sedimentary deposits of lacustrine, fluvial, eolian, and cataclysmic-flood origins compose the aquifer system of the Quincy Basin in eastern Washington. Irrigation return flow and canal leakage from the Columbia Basin Project have caused groundwater levels to rise substantially in some areas. Water resource managers are considering extraction of additional stored groundwater to supply increasing demand. To help address these concerns, the transient groundwater model of the Quincy Basin documented in this report was developed to quantify the changes in groundwater flow and storage. The model based on the U.S. Geological Survey modular three-dimensional finite-difference numerical code MODFLOW uses a 1-kilometer finite-difference grid and is constrained by logs from 698 wells in the study area. Five model layers represent two sedimentary hydrogeologic units and underlying basalt formations. Head-dependent flux boundaries represent the Columbia River and other streams, lakes and reservoirs, underflow to and (or) from adjacent areas, and discharge to agricultural drains and springs. Specified flux boundaries represent recharge from precipitation and anthropogenic sources, including irrigation return flow and leakage from water-distribution canals and discharge through groundwater withdrawal wells. Transient conditions were simulated from 1920 to 2013 using annual stress periods. The model was calibrated with the parameter-estimation code PEST to a total of 4,064 water levels measured in 710 wells. Increased recharge since predevelopment resulted in an 11.5 million acre-feet increase in storage in the Quincy Groundwater Management Subarea of the Quincy Basin. Four groundwater-management scenarios were formulated with input from project stakeholders and were simulated using the calibrated model to provide representative examples of how the model could be used to evaluate the effect on groundwater levels as a result of potential changes in recharge, groundwater withdrawals, or increased flow in Crab Creek. Decreased recharge and increased groundwater withdrawals both resulted in declines in groundwater levels over 2013 conditions, whereas increasing the flow in Crab Creek resulted in increased groundwater levels over 2013 conditions.

ABSTRACT:

Projecting the Effects of Saltwater Intrusion on the Fresh Groundwater Resources of Southeastern Louisiana and the New Orleans Area, USA, based on 3D Variable-Density Groundwater Modelling

ABSTRACT:

Numerical computation of hurricane-induced saltwater intrusion on fresh groundwater availability in peninsular Florida under different climate scenarios

ABSTRACT:

Simulation of ground-water flow in the Mojave River Basin, California

ABSTRACT:

Rhythmic springs occur when a groundwater flowpath that supplies a spring's discharge form a hydraulic siphon. The hydraulic siphon brings the spring varying fluxes of water that cycle over time. If these flows are only one flowpath in the total spring system, the influx of water from the siphon may have strong effects on water quality, but be difficult to detect in hydrograph data during spring storm response. Oscillations in electrical conductivity data were observed at Byrds Mill Spring, Pontotoc County, Oklahoma (USA). Byrds Mill Spring is the largest spring in Oklahoma by volume, and oscillations in electrical conductivity were observed during a set of extreme precipitation events in May 2015. A data logger placed at the spring's outflow recorded the electrical conductivity of the spring's oscillating between 520 ?S/cm and 10 ?S/cm multiple times while discharge remained steady. A numerical tank model was developed to simulate the electrical conductivity chemograph of Byrds Mill Spring to test hypotheses about the geometry of the siphoning system. The model simplified the karst system as a tank connected to a siphoning drain and a tank connected to a non-siphoning drain joined together by mixing at a T-junction. Using this approach, the model was able to reproduce key features of the Byrds Mill Springs chemograph. The model results provide controls on where the siphon may be located and the dimensions of the siphon system.

ABSTRACT:

The distribution coefficient (Kd) expresses the relationship between the concentration of an element, which is adsorbed in the solid surface and its remaining concentration in the solution. The Kd is a very important factor in reactive transport, representing the source/sink term, and explaining the difference between the velocity of transport of non-conservative elements (Kd > 0) and water flow velocity. In this paper, the Kd value for Zn element in loess like sediments forming the Pampeano aquifer is determined and this value is used in the modeling of reactive transport from the landfill of the city of Mar del Plata (Argentina). The determination of Kd value was done by means of batch experiments. The results obtained showed good agreement with Freundlich isotherm, with a value of K-F = 300.95 ml g(-1) and a super index value b of 0.3961. These values were applied to reactive transport modeling using Visual Modflow code. The Zn plume obtained showed the low mobility of the element in the oxidizing conditions of the environment.

ABSTRACT:

The Rio Salado catchment covers 170,000km2 of the Buenos Aires province, Argentina. The area suffers from persistent flooding situations that affect a large proportion of the catchment and hence imposes a severe constraint in the existing production levels and in the realisation of the fall economic potential of the region. The complexity of the landscape and the delicate groundwater-surface water interaction in a large dune field area made it essential to develop different approaches to model such interaction, as part of the study for an Integrated Master Plan for the whole basin. An approach using MODFLOW proved to be useful at a regional and prefeasibility level to generate flood risk maps and estimate net benefits for different drainage schemes. However ISISMOD, a groundwater model coupled with a surface water model proved to be a key water resource management tool to support feasibility studies and the detailed design of a drainage network capable of removing flood waters without detriment to the wetlands and fresh groundwater lenses of the area during dry periods.

ABSTRACT:

This paper proposes a modeling approach for assessing changes in groundwater pollution hazard under two different socio-economic and environmental scenarios: The first one considers an exponential growth of agriculture land-use (Relegated Sustainability), while the other deals with regional economic growth, taking into account, the restrictions put on natural resources use (Sustainability Reforms). The recent (2011) and forecasted (2030) groundwater pollution hazard is evaluated based on hydrogeological parameters and, the impact of land-use changes in the groundwater system, coupling together a land-use change model (Dyna-CLUE) with a groundwater flow model (MODFLOW), as inputs to a decision system support (EMDS). The Dulce Stream Watershed (Pampa Plain, Argentina) was chosen to test the usefulness and utility of this proposed method. It includes a high level of agricultural activities, significant local extraction of groundwater resources for drinking water and irrigation and extensive available data regarding aquifer features. The Relegated Sustainability Scenario showed a negative change in the aquifer system, increasing (+ 20%; high-very high classes) the contribution to groundwater pollution hazard throughout the watershed. On the other hand, the Sustainability Reforms Scenario displayed more balanced land-use changes with a trend towards sustainability, therefore proposing a more acceptable change in the aquifer system for 2030 with a possible 2% increase (high-very high classes) in groundwater pollution hazard. Results in the recent scenario (2011) showed that 54% of Dulce Stream Watershed still shows a moderate to a very low contribution to groundwater pollution hazard (mainly in the lower area). Therefore, from the point of view of natural resource management, this is a positive aspect, offering possibilities for intervention in order to prevent deterioration and protect this aquifer system. However, since it is quite possible that this aquifer status (i.e. groundwater quality) changes in the near future, the implementation of planning measures and natural resource management is recommended. (C) 2015 Elsevier B.V. All rights reserved.

ABSTRACT:

The study of the dynamics of anthropic disturbances that have an effect on the hydrological systems in plains requires integral simulation tools for their diagnosis. The objective of this article is, first, to analyse and reproduce the spatio-temporal interactions between groundwater (GW) and surface water, net recharge, GW level, surface run-off, and evapotranspiration in the upper creek basin of Del Azul, which is located in the centre of the province of Buenos Aires, Argentina, and second, to obtain insights to apply the methodology to other similar situations. For this purpose, a model coupling the semidistributed hydrological model (Soil and Water Assessment Tool [SWAT]) and the hydrogeological model (MODFLOW) has been used. A simulation was carried out for a period of 13 years (2003-2015) on a daily scale. The application of the SWAT-MODFLOW coupling gave good results based on the adjustment between the calculated flows and levels, reaching a Nash-Sutcliffe of 0.6 and R(2)0.6 at the Seminario hydrometric station located at the watershed outlet point. According to the annual average balance, out of the total rainfall, evapotranspiration accounts for 85%, recharge accounts for 10.2%, and surface run-off accounts for 4.8%. Annual and monthly trends of the stream-aquifer interaction were determined, obtaining on average an annual GW discharge of 34 mm and an annual average recharge of the stream to the aquifer of 1.4 mm. Monthly GW discharges are higher in winter-spring (July to December with an average of 3.3 mm) and lower in summer-autumn (January to June with an average of 2.8 mm). The monthly average recharge of the stream towards the aquifer varies from 0.02 to 0.36 mm and is higher in March, May, and August, when water excess is produced in the basin. Through the analysis of coupled modelling, it is possible to analyse and reproduce the spatio-temporal transitions of flow existing between the stream, the hyporheic zone, and the aquifer.

ABSTRACT:

The Peninsula Vald,s, in northeastern Patagonia, Argentina, is characterised by its arid climate and the lack of perennial watercourses; thus, all economic activities depend on the groundwater resources. Water demand is mainly associated with tourism, which is centralised in Puerto Piramides and supplied by a water desalination plant, and to sheep farming, supplied by the local aquifer. Due to the exponential growth of tourism, the government is planning to exploit groundwater and convey it by aqueduct to the abovementioned locality. The objectives of this study were to corroborate the conceptual geohydrological model, to develop a mathematical model to simulate the response of the aquifer to different scenarios, and to assess the incidence of water input into the system as a variable-a function that poses difficulties in the models for arid regions. The Visual Modflow 4.1 code was used, calibrating it in trial-and-error mode, changing the recharge and hydraulic conductivity parameters with different variants in the recharge zone and in the inclusion or exclusion of the evapotranspiration module. Results indicate the importance of the recharge analysis by treating rainfall at daily time steps. The adjusted model was exposed to four scenarios with variations in water input and in output by pumping. It can be concluded that under different input conditions, but with a controlled extraction, the system responds in a sustainable manner.

ABSTRACT:

Groundwater and surface water sourced from the high Andes of Argentina are highly important for societal, agricultural, and domestic usage in the foothills and valleys, less than hundred kilometers away from the headwaters. Despite their importance, efforts to provide estimates and predictions of surface water and especially groundwater sources and sinks have been limited. During most of the year, precipitation in the high Andes falls primarily as snow, with minimal rainfall over the summer. A widespread lack of measurements and statistical analysis in the region makes it difficult to understand groundwater storage and flow patterns in the Andean watersheds. The contribution of mountain snowmelt to groundwater is a key component of recharge to this area. While this study is limited to a small watershed in the Altar valley of the Central Andes of Argentina, it is representative of most of the Dry Andes region, which runs from Bolivia south to a latitude of 35S between Argentina and Chile. This region is characterized by steep and abrupt topography, highly fractured bedrock, and large fault systems. Here, we investigate the groundwater flow system through observations from pressure transducers and weather stations installed by a mining company exploring the area. We use this data to create a MODFLOW groundwater model of the watershed and develop then a sensitivity analysis to gain insight into the hydrologic system. We explore changes in hydraulic conductivity with depth and reduction in recharge due to uncertainties in sublimation and evaporation and potential future trends. We then analyze heads, surface outflows to assess the impact of these changes within the hydrologic system. In addition, ages distribution in particles from the one well and the river are analyzed. ? This research contributes to the understanding of groundwater recharge and discharge estimates and the hydraulic behavior of upland mountainous watersheds toward better water management in the area.

ABSTRACT:

A three-dimensional modular model (MODFLOW) was used to simulate groundwater flow in the Azul River basin. Buenos Aires Province. Argentina: in order to assess the correctness of the conceptual model of the hydrogeological system. Simulated heads satisfactorily match observed heads in the regional water-table aquifer. Model results indicate that: (1) groundwater recharge is not uniform throughout the region but is best represented by three recharge rates, decreasing downgradient, similar to the distribution of soils and geomorphological characteristics; and (2) evapotranspiration rates are larger than previous estimates, which were made by using the Thornthwaite-Mather method. Evapotranspiration rates estimated by MODFLOW agree with results of independent studies of the region. Model results closely match historical surface-flow records, thereby suggesting that the model description of the aquifer-river relationship is correct.

ABSTRACT:

This paper gives an account of the assessment and quantification of the water balance and the hydrogeological processes related to lake-groundwater interaction in the Pampa Plain by using hydrogeochemical, isotopic and flow numerical modeling techniques. La Salada is a permanent shallow lake, with an area of 5.8 km(2), located on the SE of Buenos Aires Province. A total of 29 lake water samples and 15 groundwater samples were collected for both hydrochemical analysis and environmental stable isotope determination. Water table depths were measured in wells closed to the lake. Groundwater samples appear grouped on the Local Meteoric Water Line, suggesting a well-mixed system and that rainfall is the main recharge source to the aquifer. Water evaporation process within La Salada is also corroborated by its isotopic composition. The model that best adjusts to La Salada Lake hydrochemical processes includes evaporation from groundwater, calcite precipitation with CO2 release and cationic exchange. The annual water balance terms for the lake basin indicates for each hydrological component the following values: 1.16 E-08 m(3) rainfall, 8.15 E-07 m(3) evapotranspiration, 1.90 E-06 m(3) runoff, 1.55 E-07 m(3) groundwater recharge, 6.01 E-06 m(3) groundwater discharge to the lake, 9.54 E-06 m(3) groundwater discharge to the river, 5.00 E-05 m(3) urban extraction and 4.90 E-06 m(3) lake evaporation. Integrated analysis of hydrochemical and isotopic information helped to calibrate the groundwater flow model, to validate the conceptual model and to quantitatively assess the basin water balance.

ABSTRACT:

This work describes the application of a methodology designed to improve the representation of water surface profiles along open drain channels within the framework of regional groundwater modelling. The proposed methodology employs an iterative procedure that combines two public domain computational codes, MODFLOW and HEC-RAS. In spite of its known versatility, MODFLOW contains several limitations to reproduce elevation profiles of the free surface along open drain channels. The Drain Module available within MODFLOW simulates groundwater flow to open drain channels as a linear function of the difference between the hydraulic head in the aquifer and the hydraulic head in the drain, where it considers a static representation of water surface profiles along drains. The proposed methodology developed herein uses HEC-RAS, a one-dimensional. (1D) computer code for open surface water calculations, to iteratively estimate hydraulic profiles along drain channels in order to improve the aquifer/drain interaction process. The approach is first validated with a simple closed analytical solution where it is shown that a Piccard iteration is enough to produce a numerically convergent and mass preserving solution. The methodology is then applied to the groundwater/surface water system of the Choele Choel Island, in the Patagonian region of Argentina. Smooth and realistic hydraulic profiles along drains are obtained while backwater effects are clearly represented. (C) 2008 Elsevier B.V. All rights reserved.

ABSTRACT:

The Lower Piura Sub-basin Aquifer is a vital source of water in the north of Peru. Despite its importance, few local studies describe this formation. Most are limited to reporting hydraulic characteristics and abstraction rates, lacking a broader analysis. This article characterizes the aquifer, presenting the development of a conceptual and mathematical model with sparse data, completed using several assumptions and interpolations. The model will improve understanding of the aquifer system and the impacts of abstraction. The aquifer system includes an unconfined aquifer connected to a confined aquifer through an aquitard. Steady-state and transient-state models from 2004 to 2014 were used. The development and calibration of the model have led to proper identification of hydraulic parameters and boundary conditions, clarifying the dynamics of the system. In the unconfined aquifer, groundwater flows towards the south-west without significant variation in the water table. Conversely, the piezometric surface of the confined aquifer shows a cone of depression with a falling trend of 1.6 m/year between 2004 and 2014. Outflows include abstractions (48.42 x 10(6) m(3)/year), gaining surface waters (6.33 x 10(6) m(3)/year), and sea discharge (18.50 x 10(6) m(3)/year). Inflows are from irrigation return (34.67 x 10(6) m(3)/year) and from the Higher Piura Aquifer (27.23 x 10(6) m(3)/year). The imbalance of 11.24 x 10(6) m(3)/year is abstracted from aquifer storage leading to hydraulic head drops and flow changes, revealing a clearly unsustainable overexploitation scenario that impacts more intensively the confined aquifer. Model results provide the basis to understand how this is happening and help to suggest strategies to alleviate the current aquifer situation.

ABSTRACT:

Coastal aquifers are part of the natural resources contributing to local development and promote resilience in the most vulnerable communities near the sea. Manglaralto, an Ecuadorian coastal parish, is affected by water resource scarcity. The increase in salinity and deterioration of the water quality is generated by the local and floating population's demand, causing an increase in the Total Dissolved Solids (TDS) concentrations and decreasing the aquifer's piezometric levels. The aim is to establish a numerical model of flow and transport of the Manglaralto coastal aquifer by using hydrogeological data and Visual Transin software, relating the hydraulic importance of a dyke's design ("tape") and its impact on the quality of the water. The methodology is (i) hydrogeological database analysis, (ii) the system's recharge concerning the soil water balance, (iii) the boundary conditions of the flow and transport model and, (iv) the results and validation of the numerical simulation. The results configure the importance of the coastal aquifer's artificial recharge in the area where the tape is located, as reflected in the increase in piezometric levels and the decrease in salinity in wells near the sea. In conclusion, the numerical model of flow and transport allows expanding the knowledge of the variation of the piezometric levels and TDS concentrations over time, the importance of recharge in the hydrogeological system's operation, and correct community management resilience and projection to sustainable development.

ABSTRACT:

The Chambo river basin, in central Ecuador, belongs to the watershed of the upper Pastaza, a major north-western tributary of the Amazon. It is a densely inhabited region, where the drinkable water infrastructures of the cities existing within the basin exclusively rely on the groundwater extracted from the Chambo aquifer. The results thrown by a study based on the use of the C-14 isotopes as groundwater tracers, accompanied by an overall scarcity of scientific knowledge about this hydrological system, have lead the local communities and decision makers to think that the Chambo aquifer is fossil. In this study we demonstrate that the Chambo aquifer is actually recharged over time, providing an estimate of the recharge, and showing that it is caused by the ongoing melting of the glaciers existing on top of the Chimborazo volcano. Such a scenario is compatible with the C-14 analysis, which showed that the aquifer groundwater is about 8000 years old, and suggests that a lateral water inflow actually feeds the Chambo aquifer, highlighting the present influence of the global climate change on the future water availability in central Ecuador.

ABSTRACT:

Unplanned exploitation of groundwater from coastal aquifers may cause salt water intrusion in coastal aquifers. Coastal areas are generally overpopulated with fertile agricultural lands and diversified irrigated farming activities. The objective of this study was to develop a model to control/prevent seawater intrusion into the coastal aquifer with a case study of the Silifke-Goksu Deltaic Plain. A computer program for the simulation of three-dimensional variable density groundwater flow, SEAWAT, is used to model the seawater intrusion mechanism of the Goksu Deltaic Plain along the Mediterranean coast of Turkey. The calibration analysis of the developed seawater intrusion model is performed using field measured data in the water-year of 2008 including static groundwater head, electrical conductivity, total dissolved solid (TDS), and chloride concentration values collected from 23 observation wells and the existing data which were compiled and reviewed. The main objectives for applying the seawater intrusion model to the Goksu Deltaic Plain were (1) to determine the hydraulic and hydrogeologic parameters of the aquifer, (2) to estimate the spatial variation of the salt concentration in the aquifer and (3) to investigate the impact of the increase and decrease in groundwater extractions. The simulation results show that the Goksu Deltaic Plain aquifer is especially sensitive to the increase in groundwater extraction. (C) 2012 Elsevier B.V. All rights reserved.

ABSTRACT:

In coral islands, groundwater is a crucial freshwater resource for terrestrial life, including human water supply. Response of the freshwater lens to expected climate changes and subsequent vegetation alterations is quantified for Grande Glorieuse, a low-lying coral island in the Western Indian Ocean. Distributed models of recharge, evapotranspiration and saltwater phytotoxicity are integrated into a variable-density groundwater model to simulate the evolution of groundwater salinity. Model results are assessed against field observations including groundwater and geophysical measurements. Simulations show the major control currently exerted by the vegetation with regards to the lens morphology and the high sensitivity of the lens to climate alterations, impacting both quantity and salinity. Long-term changes in mean sea level and climatic conditions (rainfall and evapotranspiration) are predicted to be responsible for an average increase in salinity approaching 140 % (+8 kg m(-3)) when combined. In low-lying areas with high vegetation density, these changes top +300 % (+10 kg m(-3)). However, due to salinity increase and its phytotoxicity, it is shown that a corollary drop in vegetation activity can buffer the alteration of fresh groundwater. This illustrates the importance of accounting for vegetation dynamics to study groundwater in coral islands.

ABSTRACT:

This study presents a method to assess the contributions of 21st-century sea-level rise and groundwater extraction to sea water intrusion in coastal aquifers. Sea water intrusion is represented by the landward advance of the 10,000 mg/L iso-salinity line, a concentration of dissolved salts that renders groundwater unsuitable for human use. A mathematical formulation of the resolution of sea water intrusion among its causes was quantified via numerical simulation under scenarios of change in groundwater extraction and sea-level rise in the 21st century. The developed method is illustrated with simulations of sea water intrusion in the Seaside Area sub-basin near the City of Monterey, California (USA), where predictions of mean sea-level rise through the early 21st century range from 0.10 to 0.90 m due to increasing global mean surface temperature. The modeling simulation was carried out with a state-of-the-art numerical model that accounts for the effects of salinity on groundwater density and can approximate hydrostratigraphic geometry closely. Simulations of sea water intrusion corresponding to various combinations of groundwater extraction and sea-level rise established that groundwater extraction is the predominant driver of sea water intrusion in the study aquifer. The method presented in this work is applicable to coastal aquifers under a variety of other scenarios of change not considered in this work. For example, one could resolve what changes in groundwater extraction and/or sea level would cause specified levels of groundwater salinization at strategic locations and times.

ABSTRACT:

The Pampa del Tamarugal Aquifer (PTA) is an important source of groundwater in northern Chile. In this study, a groundwater flow model of this aquifer is developed and calibrated for the period 1983-2004. The model reproduces the observed flow-field and the water balance components reasonably well. Five scenarios are defined to evaluate the response to different pumping situations. These scenarios show that groundwater heads will continue to decrease with the present pumping discharge rates. To account for variations in the model results due to uncertainties in average recharge rates, randomly generated recharge realizations with different levels of uncertainty are simulated. Evaporation flow rates and groundwater flowing out of the modelled area seem unaffected by the recharge uncertainty, whereas the storage terms can vary considerably. For the most intensive pumping scenario under the generated random recharge rates, it is unlikely that the cumulative discharged volume from the aquifer, at the end of the simulation period, will be larger than 12% of the estimated groundwater reserve. Fluctuations in simulated groundwater heads due to uncertainties in the average recharge values are more noticeable in certain areas. These fluctuations could explain unusual behaviour in the observed groundwater heads in these areas.

ABSTRACT:

The use of groundwater as water supply has increased dramatically in Santiago, Chile, during the last decades, and there is a need for accurately estimating the actual groundwater supply capacity in the upper Santiago Valley aquifer. The behavior of this aquifer was studied in order to determine the availability of water and the long-range sustainable extraction rate. Water-table depths were simulated using a numerical model with information on recharge from the last 48 years under different extraction policies. With this series of groundwater level data, groundwater level probability distribution functions were determined and extraction statistics were estimated by fitting time series models and by using the crossing theory. With this information, it has been possible to calculate the risk of being unable to supply groundwater demand because the results verify that only 67% of the water rights granted are able to be extracted on a sustained basis with a 90% exceedance probability. Furthermore, the results obtained demonstrate that the method is adequate for determining exceedance probabilities of groundwater flow.

ABSTRACT:

Aquifers within the Pampa del Tamarugal Basin (Atacama Desert, northern Chile) are the sole source of water for the coastal city of Iquique and the economically important mining industry. Despite this, the regional groundwater system remains poorly understood. Although it is widely accepted that aquifer recharge originates as precipitation in the Altiplano and Andean Cordillera to the east, there remains debate on whether recharge is driven primarily by near-surface groundwater flow in response to periodic flood events or by basal groundwater flux through deep-seated basin fractures. In addressing this debate, the present study quantifies spatial and temporal variability in regional-scale groundwater flow paths at 20.5A degrees S latitude by combining a two-dimensional model of groundwater and heat flow with field observations and delta O-18 isotope values in surface water and groundwater. Results suggest that both previously proposed aquifer recharge mechanisms are likely influencing aquifers within the Pampa del Tamarugal Basin; however, each mechanism is operating on different spatial and temporal scales. Storm-driven flood events in the Altiplano readily transmit groundwater to the eastern Pampa del Tamarugal Basin through near-surface groundwater flow on short time scales, e.g., 10(0)-10(1) years, but these effects are likely isolated to aquifers in the eastern third of the basin. In addition, this study illustrates a physical mechanism for groundwater originating in the eastern highlands to recharge aquifers and salars in the western Pampa del Tamarugal Basin over timescales of 10(4)-10(5) years.

ABSTRACT:

Estimating groundwater recharge in arid regions with seasonal snow cover, as in the Andean Altiplano of northern Chile, is important for sustainable development policies and the effective management of scarce resources in a high water demanding zone, as fragile ecosystems depends on a stable water contribution. This research aims to evaluate and quantify rainfall and snowfall contribution to aquifer recharge while assessing the factors that control the hydrodynamics in such areas, based in the knowledge of the better documented Tuyajto Lake in the Tuyajto catchment/basin. The modeling framework involves an energy balance of the snow cover, a soil water balance and a groundwater flow and chloride transport model. The basin average annual recharge is about 23% of average precipitation. Snowmelt contribution to recharge is important at altitudes above 4700 m a.s.l. during September, while rainfall is more important in February and March, during short intense precipitation events. The hydraulic conductivity of ignimbrites and other volcanic formations are the most important hydrogeological parameters controlling lake level and spring flow rates, while albedo and snowpack surface roughness length on the energy balance causes the greatest variation of lake level. Evaporation is the process controlling the variability of the lake level, as aquifer contribution remains relatively constant and springs flow variability is not enough to cause the observed variations, except during November. Possible buried salts deposits on the eastern edges of Pampa Colorada and Tuyajto Lake, together with volcanic HCl contribution, justify the high measured groundwater chloride concentrations. A recharge 2-3 higher than the current one is necessary to justify a lake level 40 m above its modern value during the Last Glacial period, giving insight into past hydrological changes in the basin due to climate variability. The knowledge gained can be applied to other high altitude volcanic basins with seasonal snow cover. (C) 2019 Elsevier B.V. All rights reserved.

ABSTRACT:

Agricultural production of high value crops in Chile's Central Valley is highly dependent on surface and groundwater resources. They are connected and together form an integrated hydrological system, the individual components of which have to be studied. This research is addressed to answering two questions: 1) to what extent do irrigation and canal seepage contribute to groundwater recharge and 2) what is the influence of the interactions between the Cachapoal River and ground water. The study was carried out from 2003 to 2007 in Peumo Valley (34.3 S, 71.3 W). In winter, the irrigation canal network intercepts and diverts surface runoff, which flows to flat areas and recharges groundwater. In summer, infiltration from the canals recharges the aquifer directly and partially compensates for water uptake from plants and evaporation. The effects of both interactions keep groundwater at a relatively constant level over the whole year. The water balance of the valley is strongly affected by agricultural practices, groundwater recharge mainly originating from irrigation loss (22%) and canal seepage (52%). It is important to know how management decisions, such as change in irrigation practices or canal lining, can affect the hydrological system and agricultural production within the valley.

ABSTRACT:

The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m(3)/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.

ABSTRACT:

The harsh climate, shallow and erodible soils of low fertility uplands have led to farmers extending their cultivable areas to wetlands for optimal crop production since these systems have the potential for irrigation in the dry season. Inland valleys have been cited as having high potential for development of rice-based, small-holder farming systems at the village level, due to their specific hydrological conditions and relatively high soil fertility. This paper applies a 3D groundwater flow model, PM-WIN MODFLOW to simulate the groundwater heights of the two layered alluvial aquifer of the Besease Inland Valley Bottom. Groundwater recharge estimates from the watertable fluctuation method was used as the recharge input into the model. The results showed that groundwater levels ranged from 259.10-259.97 m in the wet season and 258.19 -258.86 m in the dry season for the simulation period. It also exhibited a form of interaction between the inland valley wetland and the bordering Oda River which varied over time depending on the river stage. The values for storage from the model were substantial and indicated the temporal variability in the watertable with continuous movement of water to and from storage over an annual cycle. Sensitivity analysis was performed, and model outputs were found to be highly sensitive to the catchment parameters such as horizontal hydraulic conductivity, specific yield and specific storage. The model helps to unravel the relationship between recurrent spatial and temporal patterns of watertable response within the inland valley bottom and their controlling factors.

ABSTRACT:

Coastal plains are in the frontline of climate change. Predicted increase in recharge and sea level rise will alter groundwater flow, water quality distribution, recharge, and discharge considerably. This is simulated here in the Belgian western coastal plain. lt consists of a shore, dunes, and polder (low-lying area) with a heterogeneous groundwater reservoir of quaternary age. A three-dimensional density-dependent groundwater flow model based on numerous (hydro)geologic observations was made. First the current groundwater flow and distribution between fresh and salt water was simulated. Then the effects of a 15% recharge increase and 0.4 m of sea level rise in the next 100 years were modelled. Sea level rise results in an increased flow of fresh water toward the polder and a decreased flow toward the sea. An increase in recharge results in more water flowing toward both the polder and the sea. Brackish water present in the polder will be pushed back as is a current saltwater intrusion from the polder in the dunes. The simulations also show that groundwater levels will rise. This will put strain on the ecologically valuable dunes and the drainage system in the polders.

ABSTRACT:

Groundwater abstraction from coastal aquifers is vulnerable to climate change and sea level rise because both may potentially impact saltwater intrusion and hence groundwater quality depending on the hydrogeological setting. In the present study the impacts of sea level rise and changes in groundwater recharge are quantified for an island located in the Western Baltic Sea. The low-lying central area of the investigated part of the island was extensively drained and reclaimed during the second half of the 19th century by a system of artificial drainage canals that significantly affects the flow dynamics of the area. The drinking water, mainly for summer cottages, is abstracted from 11 wells drilled to a depth of around 20 m into the upper 5-10 m of a confined chalk aquifer, and the total pumping is only 5-6% of the drainage pumping. Increasing chloride concentrations have been observed in several abstraction wells and in some cases the WHO drinking water standard has been exceeded. Using the modeling package MODFLOW/MT3D/SEAWAT the historical, present and future freshwater-sea water distribution is simulated. The model is calibrated against hydraulic head observations and validated against geochemical and geophysical data from new investigation wells, including borehole logs, and from an airborne transient electromagnetic survey. The impact of climate changes on saltwater intrusion is found to be sensitive to the boundary conditions of the investigated system. For the flux-controlled aquifer to the west of the drained area only changes in groundwater recharge impacts the freshwater-sea water interface whereas sea level rise does not result in increasing sea water intrusion. However, on the barrier islands to the east of the reclaimed area, below which the sea is hydraulically connected to the drainage canals, and the boundary of the flow system therefore controlled, the projected changes in sea level, groundwater recharge and stage of the drainage canals all have significant impacts on saltwater intrusion and the chloride concentrations found in abstraction wells.

ABSTRACT:

Quantitative evaluation of management strategies for long-term supply of safe groundwater for drinking from the Bengal Basin aquifer (India and Bangladesh) requires estimation of the large-scale hydrogeologic properties that control flow. The Basin consists of a stratified, heterogeneous sequence of sediments with aquitards that may separate aquifers locally, but evidence does not support existence of regional confining units. Considered at a large scale, the Basin may be aptly described as a single aquifer with higher horizontal than vertical hydraulic conductivity. Though data are sparse, estimation of regional-scale aquifer properties is possible from three existing data types: hydraulic heads, C-14 concentrations, and driller logs. Estimation is carried out with inverse groundwater modeling using measured heads, by model calibration using estimated water ages based on C-14, and by statistical analysis of driller logs. Similar estimates of hydraulic conductivities result from all three data types; a resulting typical value of vertical anisotropy (ratio of horizontal to vertical conductivity) is 10(4). The vertical anisotropy estimate is supported by simulation of flow through geostatistical fields consistent with driller log data. The high estimated value of vertical anisotropy in hydraulic conductivity indicates that even disconnected aquitards, if numerous, can strongly control the equivalent hydraulic parameters of an aquifer system.

ABSTRACT:

A numerical groundwater model of the Nubian Aquifer System was established to prove the influence of rising seawater levels on the groundwater salinity in northern Egypt over the last 140,000 years. In addition, the impact of a groundwater recharge scenario for these 140,000 years, involving climatic change, on the saltwater/freshwater interface was investigated. Saltwater intrusion induced by rising water levels of the Mediterranean Sea led to salinisation from the Mediterranean Sea to the Qattara depression. This modeling approach was supported by a density-driven model setup and calculation. The modelled saltwater/freshwater interfaces partially fitted the observed ones, especially in the southern half of the Qattara depression. In other parts of the northern Nubian Aquifer System, the ingression of salt water was modelled adequately, but in the west, small regions of the measured interface were not. The development in the Qattara depression (Egypt) and Sirte basin (Libya) were investigated in more detail. The different behaviour in the Sirte basin may be due to high evapotranspiration rates in some former periods, salt solutions from the pre-Quaternary layers or saltwater infiltration from sabkha-like recent salt-bearing sediments.

ABSTRACT:

Effective porosity plays an important role in contaminant management. However, the effective porosity is often assumed to be constant in space and hence heterogeneity is either neglected or simplified in transport model calibration. Based on a calibrated highly parametrized flow model, a three-dimensional advective transport model (MODPATH) of a 1300 km(2) coastal area of southern Denmark and northern Germany is presented. A detailed voxel model represents the highly heterogeneous geological composition of the area. Inverse modelling of advective transport is used to estimate the effective porosity of 7 spatially distributed units based on apparent groundwater ages inferred from 11 C-14 measurements in Pleistocene and Miocene aquifers, corrected for the effects of diffusion and geochemical reactions. By calibration of the seven effective porosity units, the match between the observed and simulated ages is improved significantly, resulting in a reduction of ME of 99 % and RMS of 82 % compared to a uniform porosity approach. Groundwater ages range from a few hundred years in the Pleistocene to several thousand years in Miocene aquifers. The advective age distributions derived from particle tracking at each sampling well show unimodal (for younger ages) to multimodal (for older ages) shapes and thus reflect the heterogeneity that particles encounter along their travel path. The estimated effective porosity field, with values ranging between 4.3 % in clay and 45 % in sand formations, is used in a direct simulation of distributed mean groundwater ages. Although the absolute ages are affected by various uncertainties, a unique insight into the complex three-dimensional age distribution pattern and potential advance of young contaminated groundwater in the investigated regional aquifer system is provided, highlighting the importance of estimating effective porosity in groundwater transport modelling and the implications for groundwater quantity and quality assessment and management.

ABSTRACT:

A digital simulation model was used to analyze regional ground-water flow in the Madison Group aquifer in the Powder River Basin in Montana and Wyoming and adjacent areas. Most recharge to the aquifer originates in or near the outcrop areas of the Madison in the Bighorn Mountains and Black Hills, and most discharge occurs through springs and wells. Flow through the aquifer in the modeled areas was approximately 200 cubic feet per second. The aquifer can probably sustain increased ground-water withdrawals of up to several tens of cubic feet per second, but these withdrawals probably would significantly lower the potentiometric surface in the Madison aquifer in a large part of the basin. (Woodard-USGS)

ABSTRACT:

The Propopis tamarugo Phil, also known as Tamarugo, is an endemic and protected tree that survives in the Atacama Desert-a hyper arid and highly saline environment. The Tamarugo is threatened because of groundwater overexploitation, and its preservation depends on the soil moisture in the vadose zone, as many of the tree roots do not reach the current water table levels. To improve the estimation of soil moisture available for the Tamarugo trees, we applied a hydrogeological model that couples the unsaturated and saturated zones. The model was used to represent different groundwater exploitation and recharge scenarios between February 2006 and September 2030 to predict simultaneously groundwater levels and soil moisture. The model results show that even at locations where water table depletion is relatively small (1-1.5 m), soil moisture can drastically decrease (0.25-0.30 m(3)/m(3)). Therefore, Tamarugo survival can be better addressed, as the applied model provides a management tool to estimate response of Tamarugo trees to changing soil moisture. To further improve the model and its use to assess Tamarugo survival, more field data, such as soil hydrodynamic properties and soil moisture, should be collected. Additionally, relationships between the state of the Tamarugo trees and soil moisture should be further constructed. In this way, the developed model will be able to predict future conditions associated to the Tamarugo's health state.

ABSTRACT:

We investigate (a) the submarine groundwater discharge (SGWD) defined as the net groundwater discharge to the sea and (b) the typical characteristics of the spatial distribution of the groundwater outflow at the sea bottom. The investigation concerns the Eckernforde Bay in the western Baltic Sea. A large-scale groundwater model was established in order to model groundwater flow toward the sea. Due to insufficient field data, different scenarios were simulated in order to approximate the value of SGWD. It is found that the probable range of SGWD in the study area per kilometer of the land-sea interface is from 0.05 to 0.07 m(3)/s. The distribution of the groundwater outflow rates at two sea bottom sites (pockmarks) was investigated using two approaches. First, density effects were neglected. Under this condition, the resulting discharge distribution at one site is approximately uniform whereas at the other site it is strongly non-uniform with high outflow rates at the edges of the pockmark. These differences are due to different hydraulic conductivity distributions of the aquifer. Second, the investigation by means of a density-driven flow model shows that the main effect of the saltwater is to displace the groundwater outflow from the central part of the pockmark to its edges. The approximately uniform distribution estimated by neglecting the density effects does not reflect the conditions at the sea bottom whereas the strongly non-uniform distribution does. The strongly lion-uniform distribution of the outflow rates at the sea bottom indicates that locally measured outflow rates can hardly be used for the estimation of mean outflow rates over large parts of the sea bottom. (C) 2002 Elsevier Science B.V. All rights reserved.

ABSTRACT:

Over the last century, soils in the region of Nordenham in northern Germany received high loads of heavy-metals by air-borne immissions from a close-by metal smelter. Based on measured soil properties and cadmium contamination data the leaching of Cd to groundwater was predicted for Nordenham using a numerical transport model based on the convection-dispersion equation. The main objective in this study was to account for the spatial variability and uncertainty of Cd sorption controlling soil properties (pH, organic carbon content) and to analyze their propagation into the variance of area-related model outputs, i.e. Cd breakthrough concentrations at the groundwater surface. For this purpose a nested Monte-Carlo method was combined with deterministic numerical 1D simulations of Cd leaching. The transport model was parameterized without any parameter fitting involved. The validity of the model was verified by retrospective simulations from the initial operation of the smelter until the year of soil sampling. Forecast simulations were run for a period of 200 years. Predicted local scale Cd breakthrough concentrations at the groundwater surface were evaluated by spatial aggregation for single blocks at the field scale, yielding area-related concentrations with associated uncertainties from imprecise knowledge on local soil properties. Significant exceedance of the limit of the German drinking water ordinance of 5 mu g L-1 is observed on approximately 90% of the study area with the average point in time of limit value exceedance being the year 2066 and a 90% prediction interval of 2049-2092. At the end of the simulation period, Cd concentrations at the groundwater surface still increase on large parts of the study area. The spatially averaged Cd concentration is 19.89 mu g L-1 with a 90% prediction interval of 15.28-24.69 mu g L-1. Locally, however, concentrations larger than 60 mu g L-1 may be reached. Prediction uncertainty is only moderate and does not question the exceedance of the limit value on the majority of the regarded plots even for spatially averaged concentrations, unless measures to prevent leaching are taken, such as an increase of soil pH by liming. (C) 2009 Elsevier B.V. All rights reserved.

ABSTRACT:

A multilevel groundwater model was developed for the geological unit Rurscholle to forecast the impact of drainage from open pit mines on the groundwater balance and to evaluate measures to protect wetlands influenced by the drainage. The numerical model is based on a quasi-3D finite element scheme. Geological faults, wetlands, and the open pit mines are considered by a local mesh refinement. A special feature of the modelling of the open pit mines is the temporal change of the soil parameters caused by the mining process. The calibration challenges included the size of the modelling area and drainage wells with well filters in more than one aquifer. In order to reduce the number of calibration parameters, the soil parameters are divided into zones. The calibration results are presented and evaluated with examples.

ABSTRACT:

The research project GLOWA-Danube, financed by the German Federal Government, is investigating long-term changes in the water cycle of the upper Danube river basin (77,000 km(2)) in light of global climatic change. Its aim is to build a fully integrated decision-support tool "DANUBIA" that combines the competence of 11 different research institutes in domains covering all major aspects governing the water cycle-from the formation of clouds, to groundwater flow patterns, to the behaviour of the water consumer. Both the influence of natural changes in the ecosystem, such as climate change, and changes in human behaviour, such as changes in land use or water consumption, are considered. DANUBIA is comprised of 15 individual disciplinary models that are connected via customized interfaces that facilitate network-based parallel calculations. The strictly object-oriented DANUBIA architecture was developed using the graphical notation tool UML (Unified Modeling Language) and has been implemented in Java code. All models use the same spatial discretisation for the exchange of data (1 x 1 km grid cells) but are using different time steps. The representation of a vast number of relevant physical and social processes that occur at different spatial and temporal scales is a very demanding task. Newly developed up- and downscaling procedures [Rojanschi, V., 2001. Effects of upscaling for a finite-difference flow model. Master's Thesis, Institut fur Wasserbau, Universitat Stuttgart, Stuttgart, Germany] and a sophisticated time controller developed by the computer sciences group [Hennicker, R., Barth, M., Kraus, A., Ludwig, M., 2002. DANUBIA: A Web-based modelling and decision support system for integrative global change research in the upper Danube basin. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle Status Report 2002. GSF, Munich, pp. 35-38; Kraus, A., Ludwig, M., 2003. GLOWA-Danube Papers Technical Release No. 002 (Danubia Framework), Software-Release No.: 0.9.2, Documentation Version: 0.10, Release Date: 27 March 2003] are required to solve the emerging problems. After a first successful public demonstration of the DANUBIA package (nine models) in May 2002 [Mauser, W., Stolz, R., Colgan, A., 2002. GLOWA-Danube: integrative techniques, scenarios and strategies regarding global change of the water cycle. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle (Phase I, 2000-2003) Status Report 2002. GSF, Munich, pp. 31-34], the research consortium is now preparing a first validation run of DANUBIA for the period 1995-1999 with all 15 models. After successful completion of the validation, a scenario run based on IPCC climate scenarios [IPCC, 2001. Climate Change 2001: Synthesis Report. In: Watson, R.T., Core Writing Team (Eds.), A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA, 398pp] for a five year period between 2025 and 2040 will follow at the end of 2003. The research group "Groundwater and Water Resources Management" at the Institute of Hydraulic Engineering, Universitat Stuttgart, is contributing both a three-dimensional groundwater flow model of the catchment and an agent-based model for simulating water supply and distribution. This paper gives a general overview of the GLOWA-Danube project and describes the groundwater modeling segment. Nickel et al. deal with the water supply model in a second contribution to this special issue. A three-dimensional numerical groundwater flow model consisting of four main layers has been developed and is in a continual state of refinement (MODFLOW, [McDonald, M.G., Harbaugh, AW., 1988. A modular three-dimensional finite-difference ground-water flow model: US Geological Survey Techniques of Water-Resources Investigations, Washington, USA (book 6, Chapter A1)]). One main research focus has been on the investigation of upscaling techniques to meet the requirement of a fixed 1 x 1 km cell size. This cell size is compulsory for all models in DANUBIA in order to facilitate a one to one parameter exchange. In a second stage, a transport model (nitrogen) will be added (MT3D): [Zheng, C., Hathaway, D-L., 1991. MT3D: a new modular three-dimensional transport model and its application in predicting the persistence and transport of dissolved compounds from a gasoline spill, with implications for remediation. Association of Ground Water Scientists and Engineers Annual Meeting on Innovative Ground Water Technologies for the '90s, National Ground Water Association, Westerville, Ohio, USA. Ground Water 29 (5)]. (c) 2005 Elsevier Ltd. All rights reserved.

ABSTRACT:

To date, studies on the geological conditions in inland aquifers leading to pathways for upwelling deep saline groundwater due to pumping have not been published yet. Therefore, this paper conducted a theoretical modeling study to raise two hypotheses about deep saline-groundwater pathways leading to saltwater upconing below a pumping well in an inland aquifer based on the field situation at the Beelitzhof waterworks in southwestern Berlin (Germany), defined as follows: (1) there are windows in the Rupelian clay caused by glacial erosion, where their locations are uncertain, and (2) there are no windows in the clay, but the clay is partially thinned out but not completely removed by glacial erosion, so salt can merely come through the clay upward by diffusion and eventually accumulate on its top. These hypotheses were tested to demonstrate the impact of the lateral distance between windows in the clay and the well, as well as salt diffusion through the clay depending on its thickness on saltwater intrusion in the pumping well, respectively, using a density-dependent groundwater flow and solute transport model. Hypothesis 1 was validated with four scenarios that windows could occur in the clay at the site, and their locations under some conditions could significantly cause saltwater intrusion, while hypothesis 2 could be excluded, because salt diffusion through the clay with thickness greater than 1 m at the site was not able to cause saltwater intrusion.

ABSTRACT:

Ecosystems in river valleys are affected mainly by the hydraulic conditions in wetlands including groundwater dynamics. The quantitative prediction of changes in groundwater dynamics caused by river embankment relocation requires numerical modelling using a physically-based approach. Groundwater recharge from the intermittently flooded river plains was determined by a leakage approach considering soil hydraulic properties. For the study area in the Elbe river valley north of Magdeburg, Germany, a calibrated groundwater flow model was established and the groundwater dynamics for the present situation as well as for the case of embankment relocation were simulated over a 14-year time period. Changes in groundwater depth derived from simulated groundwater levels occurred only during flood periods. By analysing the spatial distributions of changes in statistical parameters, those areas with significant impact on the ecosystems by embankment relocation can be determined.

ABSTRACT:

This publication discusses the computer program development of the "Groundwater Model for the Netherlands (LGM)". The publication is also intended to be a user's guide. It describes the various steps to be taken and procedures to be observed throughout the modelling process while applying LGM. LGM is a coupled system of so-called AQ-computer program packages and the Geographic Information System (GIS). The communication between the AQ-environment and the GIS-environment is based on ASCII files. The AQ programs are based on the numerical technique of finite elements (triangles and quadrilaterals). The saturated multi-aquifer geohydrological system consists of a series of aquifers separated by aquitards. Presently, the main output of simulations with LGM are maps of groundwater heads in aquifer, flux between the upper boundary of the geohydrological system and the top system, and fluxes across the aquitards. LGM can be used to assess the effect of various stresses upon the geohydrological system, for example due to changes in groundwater abstraction. LGM proves to be an efficient and versatile tool to address various types of geohydrological problems.

ABSTRACT:

Basal water pressure and water flow patterns are significant factors in controlling the behavior of an ice sheet, because they influence ice-sheet thickness, stability and extent. Water produced by basal melting may infiltrate the subsurface, or occur as sheet or channelized flow at the ice/bed interface. We examine subglacial groundwater conditions along a flowline of the Scandinavian ice sheet through Nordfjord, in the western fjords region of southern Norway, using a steady-state, two-dimensional groundwater-flow model. Meltwater input to the groundwater model is calculated by a two-dimensional, time-dependent, thermomechanically coupled ice-flow model oriented along the same flowline. Model results show that the subglacial sediments could not have transmitted all the meltwater out of the fjord during times of ice advance and when the ice sheet was at its maximum position at the edge of the continental shelf. In order for pore-water pressures to remain below the overburden pressure of the overlying ice, other paths of subglacial drainage are necessary to remove excess water. During times of retreat, the subglacial aquifer is incapable of transmitting all the meltwater that was probably generated. Pulses of meltwater reaching the bed could explain non-climatically driven margin readvances during the overall retreat phase.

ABSTRACT:

Using a modified version of the USGS MODFLOW code, coupled with a Penman- Grindley type recharge model, it has been possible to produce a transient, 3- dimensional groundwater flow model of the Ovre Romerike aquifer. A steady state model has been calibrated against 183 regional water level observation data from autumm 1975 and against the flows in groundwater-fed springs and streams. The distribution of hydraulic conductivity calibrated using the steady state model was then used to simulate water table variations over a period in excess of 30 years at 3 observation wells. The results show a satisfactory fit with real data, allowing for the limited spatial resolution of the model. A sevenmonth running average filter has been applied to the re- charge data to simulate the damping effects of the unsaturated zone on recharge naxima and minima, resulting in an even better fit. The modelling work has enabled the project's participants to obtain a deeper understanding of the hydraulics of the aquifer, and has also indicated that hydraulic conductivity values obtained from grain size distributions tend to lead to underestimates of aquifer transmissivity. The model provides a framework for further modelling work on contaminant transport at Trandum land- fill.

ABSTRACT:

A numerical flow and transport model is developed to assess groundwater discharge and nutrient transport to the Ria Formosa coastal lagoon in southern Portugal. A total N load of 350 ton/year is estimated for the considered area, of which agriculture accounts for 73% of total N load, and domestic effluent and atmospheric deposition for the remaining 9% and 18% respectively. Model results suggest that nutrient recycling has led to the high concentrations observed in the Campina de Faro (M12) aquifer, but is still insufficient to account for observed values at the coastline. Furthermore results suggest that even for the best case mitigation scenario, good quality status will not be achieved by 2027, as mandated by the EU Water Framework Directive. (C) 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.

ABSTRACT:

The cities of Rivera and Santana do Livramento are located on the outcropping area of the sandstone Guarani Aquifer on the Brazil-Uruguay border, where the aquifer is being increasingly exploited. Therefore, recharge estimates are needed to address sustainability. First, a conceptual model of the area was developed. A multilayer, heterogeneous and anisotropic groundwater-flow model was built to validate the conceptual model and to estimate recharge. A field campaign was conducted to collect water samples and monitor water levels used for model calibration. Field data revealed that there exists vertical gradients between confining basalts and underlying sandstones, suggesting basalts could indirectly recharge sandstone in fractured areas. Simulated downward flow between them was a small amount within the global water budget. Calibrated recharge rates over basalts and over outcropping sandstones were 1.3 and 8.1% of mean annual precipitation, respectively. A big portion of sandstone recharge would be drained by streams. The application of a water balance yielded a recharge of 8.5% of average annual precipitation. The numerical model and the water balance yielded similar recharge values consistent with determinations from previous authors in the area and other regions of the aquifer, providing an upper bound for recharge in this transboundary aquifer.

ABSTRACT:

The analysis of the impact of climate change on water resources in plains requires integral simulation tools that quantify topographic complexity and the strong interaction of groundwater and surfacewater components (GW-SW). The objective of this study is to implement a coupled hydrological-hydrogeological model under climate change scenarios in order to quantify the spatio-temporal dynamics of water balance and GW-SW interactions for the upper creek basin of Del Azul, which is located in the center of the province of Buenos Aires. The simulation was carried out for a baseline scenario calibrated and validated for the period 2003-2015 and contrasted with two scenarios of the regional climate model CCSM4, RCP (4.5 and 8.5) simulated for the period 2020-2050. First, the annual andmonthly anomalies of precipitation, temperature, surface runoff, evapotranspiration, soilmoisture, recharge, flow, aswell as the discharge, head level and reserves of groundwater are studied. Then the spatio-temporal anomalies of the GW-SWinteraction were analyzed and finallywet and dry periods by means of the standardized precipitation index and the annual water balance were studied. Simulation results show that climate change will significantly alter the spatio-temporal patterns of the GW-SW interaction as well as the water balance. These showed monthly, seasonal and annual variations. They show an increase in most of the components of the water balance towards the middle of the 21st century, except soil moisture. Regarding GW-SW interactions, the average annual discharge of the aquifer to the stream is expected to increase by 5% with RCP 4.5while itwill increase 24% with RCP 8.5. The recharge fromthe streamto the aquifer is expected to increase by 12% with RCP 4.5while a decrease by 5% with RCP 8.5. Concerning the SPI related to the water balance for the period 2020-2050, alternations of both the time and the length of dry and wet periods are expected for the two scenarios, with RCP 4.5 lowfrequency ofwet episodes, butwith a greater severity and permanence in time in contrast to RCP 8.5 that presents less frequency in dry periods, but with high permanence and severity. Climate change could alter groundwater mainly through changes in the recharge, leading tomodify groundwater levels and this will cause GW-SWflow to be reversed in some sectors of the stream by increasing or decreasing groundwater discharge into the stream. (C) 2020 Elsevier B.V. All rights reserved.

ABSTRACT:

The application of computer simulation models plays a significant role in the understanding of water dynamics in basins. The recent and explosive growth of the processing capabilities of General-Purpose Graphics Processing Units (GPGPUs) has resulted in widespread interest in parallel computing from the modelling community. In this paper, we present a GPGPU implementation of finite-differences solution of the equations of the 2D groundwater flow in unconfined aquifers for heterogeneous and anisotropic media. We show that the GPGPU-accelerated solution implemented using CUDA(1) C/C++ largely outperforms the corresponding serial solution in C/Cthornthorn. The results show that the GPGPU-accelerated implementation is capable of providing up to a 56-fold speedup in the solution using an ordinary office computer equipped with an inexpensive GPU(2) card. The code developed for this research is available for download and use at http://modelagemambientaluffs.blogspot.com.br/. (C) 2017 Elsevier Ltd. All rights reserved.
Note: Bounding box set based on locaiton of Brazil generally since exact location unknown.

ABSTRACT:

The estimation of groundwater recharge volume is a crucial requirement for the management of subsurficial water resources. The implementation of monitoring of the water table in shallow aquifers allows the seasonal variation in the water table induced by natural and anthropogenic factors. The assessment of groundwater recharge through analysis of the water table is commonly estimated by the water table fluctuation (WTF) method, an approach subject to uncertainty. Aiming to improve estimation of groundwater recharge, we proposed and tested a simple approach combining a numerical flow model with statistical analysis of cross-correlation. Our strategy produces a time-series of recharge that is able to generate the observed water-table fluctuation and may be especially useful in analyses of the hydrological balance. The obtained results showed that our approach was suitable and was capable of producing a time-series of monthly recharge, with groundwater recharge comprising 17% of total precipitation. The cross-correlation indicates that the most significant correlation (0.63) between precipitation and groundwater recharge is observed at a time lag of 1.5 months, suggesting fast movement of precipitated water toward the unsaturated zone.

ABSTRACT:

SRV MODFLOW model development began in the late 1980's. Previous to the late 1980's, two groundwater models within the Salt River Valley had been developed. Thomas Anderson (1968) developed an electric analog model simulating the groundwater depletion of Central Arizona between 1923 and 1964. In 1982 Long et al. developed a USGS Trescott Model which simulated 1964 - 1977. Since the first SRV MODFLOW release in 1994 the model has undergone several updates with the most recent update completed in 2009 (transient calibration period 1983-2006). The SRV model geology was updated in 2010 and expanded the model grid to include the Hassayampa sub-basin. The next SRV model update is currently in the initial phase of development and plans to include a simulation of steady state (circa 1900) and transient (1901-2011) conditions.

ABSTRACT:

The Indian Creek Basin in the southwestern Piedmont of North Carolina is one of five type areas studied as part of the Appalachian Valleys-Piedmont Regional Aquifer-System analysis. Detailed studies of selected type areas were used to quantify ground-water flow characteristics in various conceptual hydrogeologic terranes. The conceptual hydrogeologic terranes are considered representative of ground-water conditions beneath large areas of the three physiographic provinces--Valley and Ridge, Blue Ridge, and Piedmont--that compose the Appalachian Valleys-Piedmont Regional Aquifer-System Analysis area. The Appalachian Valleys-Piedmont Regional Aquifer-System Analysis study area extends over approximately 142,000 square miles in 11 states and the District of Columbia in the Appalachian highlands of the Eastern United States. The Indian Creek type area is typical of ground-water conditions in a single hydrogeologic terrane that underlies perhaps as much as 40 percent of the Piedmont physiographic province. The hydrogeologic terrane of the Indian Creek model area is one of massive and foliated crystalline rocks mantled by thick regolith. The area lies almost entirely within the Inner Piedmont geologic belt. Five hydrogeologic units occupy major portions of the model area, but statistical tests on well yields, specific capacities, and other hydrologic characteristics show that the five hydrogeologic units can be treated as one unit for purposes of modeling ground-water flow. The 146-square-mile Indian Creek model area includes the Indian Creek Basin, which has a surface drainage area of about 69 square miles. The Indian Creek Basin lies in parts of Catawba, Lincoln, and Gaston Counties, North Carolina. The larger model area is based on boundary conditions established for digital simulation of ground-water flow within the smaller Indian Creek Basin. The ground-water flow model of the Indian Creek Basin is based on the U.S. Geological Survey?s modular finite-difference ground-water flow model. The model area is divided into a uniformly spaced grid having 196 rows and 140 columns. The grid spacing is 500 feet. The model grid is oriented to coincide with fabric elements such that rows are oriented parallel to fractures (N. 72 E.) and columns are oriented parallel to foliation (N. 18 W.). The model is discretized vertically into 11 layers; the top layer represents the soil and saprolite of the regolith, and the lower 10 layers represent bedrock. The base of the model is 850 feet below land surface. The top bedrock layer, which is only 25 feet thick, represents the transition zone between saprolite and unweathered bedrock. The assignment of different values of transmissivity to the bedrock according to the topographic setting of model cells and depth results in inherent lateral and vertical anisotropy in the model with zones of high transmissivity in bedrock coinciding with valleys and draws, and zones of low transmissivity in bedrock coinciding with hills and ridges. Lateral anisotropy tends to be most pronounced in the north-northwest to south-southeast direction. Transmissivities decrease nonlineraly with depth. At 850 feet, depending on topographic setting, transmissivities have decreased to about 1 to 4 percent of the value of transmissivity immediately below the regolith-bedrock interface. The model boundaries are, for the most part, specified-flux boundaries that coincide with streams that surround the Indian Creek Basin. The area of active model nodes within the boundaries is about 146 square miles and has about 17,400 active cells. The numerical model is designed not as a predictive tool, but as an interpretive one. The model is designed to help gain insight into flow-system dynamics. Predictive capabilities of the numerical model are limited by the constraints placed on the flow system by specified fluxes and recharge distribution.

ABSTRACT:

The Water Department at the North Littoral Regional University Center of the Republic University (UDELAR) and the National Water Directorate of Uruguay (DINAGUA) developed a numerical model of the Guarani Aquifer for managing the thermal wells in the area of Concordia (Entre Rios, Argentina) and Salto (Uruguay). The model geometry was built integrating geological and geophysical information. The contact surfaces of the sedimentary package with basalt and basement was reconstructed. By reinterpreting pumping tests estimates transmissivity and storage coefficient. Due to the shortage of piezometric measures the calibration process was carried out simulating the evolution of the aquifer from 1992 to 2002, considering the piezometric levels obtained at the time a new well was drill. Through a series of model simulations the requirements that DINAGUA demands to grant operating licenses in Uruguayan were evaluated. By modelling a set of scenarios the minimum distance criterion that future wells must maintain with existing was assessed. The results showed that, some scenarios that meet the current criteria have a greater impact on the system than others who do not. This highlights the need to consider mathematical modelling in the criteria design for aquifer management, and especially in assessing the impact of specific actions on the system. Keywords: Guarani Aquifer, mathematical model, Well-management, policy evaluation.

ABSTRACT:

Troia-Melides is a sandy area on SW Portugal, between Lisbon and Algarve, on the Atlantic Portuguese coast. The top north of the tract is a sandy peninsula about 10 kin long and 2 to 4 kin large, and is represented by recent dynamic sand-dune systems (Plio-Plistocene-Halocene) that extends south to the rocky Sines Cape, in a total-extension of 65 km (far beyond the zone covered by this work, that corresponds to northern half of this extension). The central zone of the littoral arch has sandstone cliffs headed by ancient dunes separated from the actual beach, which is continuous along the tract. A great diversity of important ecosystems characterises all the area, conferring it an enormous ecological fragility. Besides the dune and cliffs systems, 3 important coastal lagoons are also present. This diversity. of coastal environments was responsible for the definition of protected areas, classified according the more important species (birds, rare plants). Concerning flora, 45 families belonging to 246 different species where identified in a recent study. The major percentage occupies the inner dunes and includes several priority species (Directive 92/43/CEE) - Lonopsidium acaule, Thymus camphoratus, Linaria ficalhoana, etc. A scarce variety occurs in primary and embryonic dunes (being Ammophila arenaria the most common). This area has a great touristic potential, which is not always in conciliation with its fragile ecology. However, it's a relatively well-preserved tract and is nowadays under strict land management rules. In the study area, 3 touristic areas are approved, with a total number of 39,300 touristic beds, distributed by hotels and vacation houses. As a result, some delicate situations have occurred in natural ecosystems, namely aquifer exploitation, without regarding its recharge capacity, which lead to the infiltration of saline water in the aquifers of the littoral areas. With this work it was possible to understand the role of the saltwater intrusion due to the raise of buildings and fresh groundwater demands, and the previsible impacts on coastal ecosystems. Some procedures were undertaken in order to know the hydrogeochemistry and hydrodynamical characteristics of the aquifers in the area, namely defining the thickness of the fresh groundwater and the position of the interface with the saline water on the coastal area

ABSTRACT:

This study was undertaken to characterize ground- water flow in the Stony Brook, Beden Brook, and Jacobs Creek drainage basins in west-central New Jersey. The 89-square-mile study area is underlain by dipping beds of fractured siltstone, shale, and sandstone and by massive diabase sills. In all of the rocks, the density of interconnected fractures decreases with depth. A major fault extends through the study area, and rocks on both sides of the fault are extensively fractured. The average annual rates of precipitation and ground-water recharge in the study area are 45.07 inches and 8.58 inches, respectively. The rate of recharge to diabase rocks is about one-half the rate of recharge to other rocks. Part of the surface runoff from diabase rocks enters the ground-water system where it encounters more permeable rocks. Most ground water in the study area follows short, shallow flow paths. A three- dimensional finite-difference model of ground-water flow was developed to test hypotheses concerning geologic features that control ground-water flow in the study area. The decrease in the density of interconnected fractures with depth was represented by dividing the model into two layers with different hydraulic conductivity. The pinching out of water- bearing beds in the dip direction at land surface and at depth was simulated as a lower hydraulic conductivity in the dip direction than in the strike direction. This model can be used to analyze ground-water flow if the area of interest is more than about 0.5 square mile.

ABSTRACT:

The U.S. Geological Survey developed a groundwater-flow model for the uppermost principal aquifer systems in the Williston Basin in parts of Montana, North Dakota, and South Dakota in the United States and parts of Manitoba and Saskatchewan in Canada as part of a detailed assessment of the groundwater availability in the area. The assessment was done because of the potential for increased demands and stresses on groundwater associated with large-scale energy development in the area. As part of this assessment, a three-dimensional groundwater-flow model was developed as a tool that can be used to simulate how the groundwater-flow system responds to changes in hydrologic stresses at a regional scale. The three-dimensional groundwater-flow model was developed using the U.S. Geological Survey's numerical finite-difference groundwater model with the Newton-Rhapson solver, MODFLOW-NWT, to represent the glacial, lower Tertiary, and Upper Cretaceous aquifer systems for steady-state (mean) hydrological conditions for 1981?2005 and for transient (temporally varying) conditions using a combination of a steady-state period for pre-1960 and transient periods for 1961?2005. The numerical model framework was constructed based on existing and interpreted hydrogeologic and geospatial data and consisted of eight layers. Two layers were used to represent the glacial aquifer system in the model; layer 1 represented the upper one-half and layer 2 represented the lower one-half of the glacial aquifer system. Three layers were used to represent the lower Tertiary aquifer system in the model; layer 3 represented the upper Fort Union aquifer, layer 4 represented the middle Fort Union hydrogeologic unit, and layer 5 represented the lower Fort Union aquifer. Three layers were used to represent the Upper Cretaceous aquifer system in the model; layer 6 represented the upper Hell Creek hydrogeologic unit, layer 7 represented the lower Hell Creek aquifer, and layer 8 represented the Fox Hills aquifer. The numerical model was constructed using a uniform grid with square cells that are about 1 mile (1,600 meters) on each side with a total of about 657,000 active cells. Model calibration was completed by linking Parameter ESTimation (PEST) software with MODFLOW-NWT. The PEST software uses statistical parameter estimation techniques to identify an optimum set of input parameters by adjusting individual model input parameters and assessing the differences, or residuals, between observed (measured or estimated) data and simulated values. Steady-state model calibration consisted of attempting to match mean simulated values to measured or estimated values of (1) hydraulic head, (2) hydraulic head differences between model layers, (3) stream infiltration, and (4) discharge to streams. Calibration of the transient model consisted of attempting to match simulated and measured temporally distributed values of hydraulic head changes, stream base flow, and groundwater discharge to artesian flowing wells. Hydraulic properties estimated through model calibration included hydraulic conductivity, vertical hydraulic conductivity, aquifer storage, and riverbed hydraulic conductivity in addition to groundwater recharge and well skin. The ability of the numerical model to accurately simulate groundwater flow in the Williston Basin was assessed primarily by its ability to match calibration targets for hydraulic head, stream base flow, and flowing well discharge. The steady-state model also was used to assess the simulated potentiometric surfaces in the upper Fort Union aquifer, the lower Fort Union aquifer, and the Fox Hills aquifer. Additionally, a previously estimated regional groundwater-flow budget was compared with the simulated steady-state groundwater-flow budget for the Williston Basin. The simulated potentiometric surfaces typically compared well with the estimated potentiometric surfaces based on measured hydraulic head data and indicated localized groundwater-flow gradients that were topographically controlled in outcrop areas and more generalized regional gradients where the aquifers were confined. The differences between the measured and simulated (residuals) hydraulic head values for 11,109 wells were assessed, which indicated that the steady-state model generally underestimated hydraulic head in the model area. This underestimation is indicated by a positive mean residual of 11.2 feet for all model layers. Layer 7, which represents the lower Hell Creek aquifer, is the only layer for which the steady-state model overestimated hydraulic head. Simulated groundwater-level changes for the transient model matched within plus or minus 2.5 feet of the measured values for more than 60 percent of all measurements and to within plus or minus 17.5 feet for 95 percent of all measurements; however, the transient model underestimated groundwater-level changes for all model layers. A comparison between simulated and estimated base flows for the steady-state and transient models indicated that both models overestimated base flow in streams and underestimated annual fluctuations in base flow. The estimated and simulated groundwater budgets indicate the model area received a substantial amount of recharge from precipitation and stream infiltration. The steady-state model indicated that reservoir seepage was a larger component of recharge in the Williston Basin than was previously estimated. Irrigation recharge and groundwater inflow from outside the Williston Basin accounted for a relatively small part of total groundwater recharge when compared with recharge from precipitation, stream infiltration, and reservoir seepage. Most of the estimated and simulated groundwater discharge in the Williston Basin was to streams and reservoirs. Simulated groundwater withdrawal, discharge to reservoirs, and groundwater outflow in the Williston Basin accounted for a smaller part of total groundwater discharge. The transient model was used to simulate discharge to 571 flowing artesian wells within the model area. Of the 571 established flowing artesian wells simulated by the model, 271 wells did not flow at any time during the simulation because hydraulic head was always below the land-surface altitude. As hydraulic head declined throughout the simulation, 68 of these wells responded by ceasing to flow by the end of 2005. Total mean simulated discharge for the 571 flowing artesian wells was 55.1 cubic feet per second (ft3/s), and the mean simulated flowing well discharge for individual wells was 0.118 ft3/s. Simulated discharge to individual flowing artesian wells increased from 0.039 to 0.177 ft3/s between 1961 and 1975 and decreased to 0.102 ft3/s by 2005. The mean residual for 34 flowing wells with measured discharge was 0.014 ft3/s, which indicates the transient model overestimated discharge to flowing artesian wells in the model area. Model limitations arise from aspects of the conceptual model and from simplifications inherent in the construction and calibration of a regional-scale numerical groundwater-flow model. Simplifying assumptions in defining hydraulic parameters in space and hydrologic stresses and time-varying observational data in time can limit the capabilities of this tool to simulate how the groundwater-flow system responds to changes in hydrologic stresses, particularly at the local scale; nevertheless, the steady-state model adequately simulated flow in the uppermost principal aquifer systems in the Williston Basin based on the comparison between the simulated and estimated groundwater-flow budget, the comparison between simulated and estimated potentiometric surfaces, and the results of the calibration process.

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Leakage from water mains, storm drainage and sewer systems in urban areas constitutes a source of recharge that is difficult to identify and quantify at a regional scale. The objective of this work is to apply a methodology that would make it possible to evaluate urban recharge at a regional scale, taking as a case study the city of La Plata (Argentina). In the study area, population growth and an increase in water demand has caused the intensive exploitation of groundwater with resulting alteration in groundwater flow. The methodology used was developed on the basis of a water balance and the simulation of the temporal evolution of the cones of depression and the volumes of water extracted from the aquifer. The method consists of adjusting the piezometry resulting from the numerical modelling to the measured piezometry, by means of the variation of the recharge parameter in the urban area. The results obtained make it possible to identify and quantify urban recharge, which in this case represents a volume of water similar to the recharge from precipitation.

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This report describes the geohydrology of the Salinas to Patillas area of the South Coastal Plain aquifer system in Puerto Rico.

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This is a large modelencompassing the main aquifers of the central US a saprt of the USGS RASA program. There is no DOI associated with report, and reprot is too large to be uploaded, but can be found at https://pubs.usgs.gov/pp/1414c/report.pdf

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Groundwater flow modeling was used to quantitatively assess the hydrologic processes affecting groundwater and solute movement to drain laterals. Modeling results were used to calculate the depth distribution of groundwater flowing into drain laterals at 1.8 m (drain lateral 1) and 2.7 m (drain lateral 2) below land surface. The simulations indicated that under nonirrigated conditions about 89% of the flow in drain lateral 2 was from groundwater originating from depths greater than 6 m below land surface. The deep groundwater has higher selenium concentrations than shallow groundwater. Simulation of irrigated conditions indicates that as recharge (deep percolation) increases, the proportional contribution of deep groundwater to drain lateral flow decreases. Groundwater flow paths and travel times estimated from the simulation results indicate that groundwater containing high concentrations of selenium (greater than 780-mu-g L-1) probably will continue to enter drain lateral 2 for decades.

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The occurrence of selenium in agricultural drain water from the western San Joaquin Valley, California, has focused concern on the semiconfined ground-water flow system, which is underlain by the Corcoran Clay Member of the Tulare Formation. A two-step procedure is used to calibrate a preliminary model of the system for the purpose of determining the steady-state hydraulic properties. Horizontal and vertical hydraulic conductivities are modeled as functions of the percentage of coarse sediment, hydraulic conductivities of coarse-textured (K(coarse)) and fine-textured (K(fine)) end members, and averaging methods used to calculate equivalent hydraulic conductivities. The vertical conductivity of the Corcoran (K(corc)) is an additional parameter to be evaluated. In the first step of the calibration procedure, the model is run by systematically varying the following variables: (1) K(coarse)/K(fine), (2) K(coarse)/K(corc), and (3) choice of averaging methods in the horizontal and vertical directions. Root mean square error and bias values calculated from the model results are functions of these variables. These measures of error provide a means for evaluating model sensitivity and for selecting values of K(coarse), K(fine), and K(corc) for use in the second step of the calibration procedure. In the second step, recharge rates are evaluated as functions of K(coarse), K(corc), and a combination of averaging methods. The associated K(fine) values are selected so that the root mean square error is minimized on the basis of the results from the first step. The results of the two-step procedure indicate that the spatial distribution of hydraulic conductivity that best produces the measured hydraulic head distribution is created through the use of arithmetic averaging in the horizontal direction and either geometric or harmonic averaging in the vertical direction. The equivalent hydraulic conductivities resulting from either combination of averaging methods compare favorably to field- and laboratory-based values.

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A MODFLOW model of the Columbia River flood basalts in the Pacific Northwest of the United Stares.

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In large mountainous catchments, shallow unconfined alluvial aquifers play an important role in conveying Subsurface runoff to the foreland. Their relatively small extent poses a serious problem for ground water flow models on the river basin scale. River basin scale models describing the entire water cycle are necessary in integrated water resources management and to study the impact of global climate change on ground water resources. Integrated regional-scale models must use a coarse, fixed discretization to keep computational demands low and to facilitate model Coupling. This can lead to discrepancies between model discretization and the geometrical properties of natural systems. Here. an approach to overcome this discrepancy is discussed using the example of the German-Austrian Upper Danube catchment, where a coarse ground water flow model was developed using MODFLOW. The method developed uses a modified concept from a hydrological catchment drainage analysis in order to adapt the aquifer geometry such that it respects the numerical requirements of the chosen discretization, that is, the width and the thickness of cells as well as gradients and connectivity of the catchment. In order to show the efficiency of the developed method, it was tested and compared to a finely discretized ground water model of the Ammer subcatchment. The results of the analysis prove the applicability of the new approach and contribute to the idea of using physically based ground water models in large catchments.

ABSTRACT:

In large mountainous catchments, shallow unconfined alluvial aquifers play an important role in conveying Subsurface runoff to the foreland. Their relatively small extent poses a serious problem for ground water flow models on the river basin scale. River basin scale models describing the entire water cycle are necessary in integrated water resources management and to study the impact of global climate change on ground water resources. Integrated regional-scale models must use a coarse, fixed discretization to keep computational demands low and to facilitate model Coupling. This can lead to discrepancies between model discretization and the geometrical properties of natural systems. Here. an approach to overcome this discrepancy is discussed using the example of the German-Austrian Upper Danube catchment, where a coarse ground water flow model was developed using MODFLOW. The method developed uses a modified concept from a hydrological catchment drainage analysis in order to adapt the aquifer geometry such that it respects the numerical requirements of the chosen discretization, that is, the width and the thickness of cells as well as gradients and connectivity of the catchment. In order to show the efficiency of the developed method, it was tested and compared to a finely discretized ground water model of the Ammer subcatchment. The results of the analysis prove the applicability of the new approach and contribute to the idea of using physically based ground water models in large catchments.

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Thr Amsterdam Water Supply has been using both the finite difference model MODFLOW (McDonald, M.G., Harbaugh, A.W., 1989. A modular three-dimensional finite-difference ground water flow model. Chapter Al, USGS, Book 6, Modeling Techniques) and the analytic element model MLAEM (Strack, O.D.L,, 1989. Groundwater Mechanics. Prentice Hall, Englewood Cliffs, NJ, (ISBN 0-13-365412-5); Strack, O.D.L,, 1999. Principles of the analytic element method. Journal of Hydrology, 226, 128-138) for many years. Choosing one or the other depends on the hydrologic system, its scale and the hydrologic features to be taken into account. Either method has its specific advantages. (C) 1999 Elsevier Science B.V. All rights reserved.

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In 1985, I attended the first course on analytic element modeling in the Netherlands, where Professor Otto Strack of the University of Minnesota presented his newly conceived analytic element method (AEM; Strack 1989) at the Technical University Delft from which he graduated years before. While he explained the principles and applications of the method, I started to realize that the AEM might be uniquely suited to modeling detailed ground water flow systems covering large regions because it enables cutting, pasting, and linking of entire models as well as of model parts. In 1987, at the National Institute for Inland Water Management and Waste Water Treatment in the Netherlands (RIZA), there was much interest in national modeling in the Netherlands because of serious water management problems that first became apparent during the major drought of 1976. In fact, there existed a national water management system of models, called PAWN (Policy Analysis for Water management in the Netherlands; Rand Corporation 1982). PAWN is an integrated system of models for simulating the distribution over the numerous national and regional surface waters in this wet country and the effects on agriculture, nature (ecology), power plants, shipping, flushing of coastal areas against salt water intrusion, and drinking water. PAWN was lacking treatment of the ground water reservoir, which had become apparent in the policy analysis of 1985 (Pulles 1985). The NAtional GROundwater Model (NAGROM) should cover this gap as part of PAWN.

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Hydrogeological modelling of the Kampinos National Park (KNP) region has been carried out. The KNP comprises a hydrogeological unit of valley relatively simple structure, and has been investigated empirically and theoretically since the 1970's. Results of numerical modelling given here provide a quantitative evaluation of hydrogeological parameters, recharging infiltration, river drainage and evapotranspiration processes (groundwater evaporation), water balance and the role of hydrodynamic zones in the recharge and drainage contribution in the water balance of the Vistula valley unit.

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The study of water quality and the quantification of reserves and their variations according to natural and anthropogenic forcing is necessary to establish an adequate management plan for groundwater resources. For this purpose, a modeling approach is a useful tool that allows, after calibration phase and verification of simulation, and under different scenarios of forcing and operational changes, to estimate and control the groundwater quantity and quality. The main objective of this study is to collect all available data in a model that simulates the Jeffara of Medenine coastal aquifer system functioning. To achieve this goal, a conceptual model was constructed based on previous studies and hydrogeological investigations. The regional groundwater numerical flow model for the Jeffara aquifer was developed using MODFLOW working under steady-state and transient conditions. Groundwater elevations measured from the piezometric wells distributed throughout the study area in 1973 were selected as the target water levels for steady state (head) model calibration. A transient simulation was undertaken for the 42 years from 1973 to 2015. The historical transient model calibration was satisfactory, consistent with the continuous piezometric decline in response to the increase in groundwater abstraction. The developed numerical model was used to study the system's behavior over the next 35 years under various constraints. Two scenarios for potential groundwater extraction for the period 2015-2050 are presented. The predictive simulations show the effect of the increase of the exploitation on the piezometric levels. To study the phenomenon of salinization, which is one of the most severe and widespread groundwater contamination problems, especially in coastal regions, a solute transport model has been constructed by using MT3DMS software coupled with the groundwater flow model. The best calibration results are obtained when the connection with the overlying superficial aquifer is considered suggesting that groundwater contamination originates from this aquifer. Recommendations for water resource managers The results of this study show that Groundwater resources of Jeffara of Medenine coastal aquifer in Tunisia are under immense pressure from multiple stresses. The water resources manager must consider the impact of economic and demographic development in groundwater management to avoid the intrusion of saline water. The results obtained presented some reference information that can serve as a basis for water resources planning. The model runs to provide information that managers can use to regulate and adequately control the Jeffara of Medenine water resources.

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Recent climate change studies for the Mediterranean region have projected the near future temperature and precipitation trends. The increasing water demands for human consumption and agricultural purposes, as well as the potential overexploitation of the groundwater resources, in combination with the climatic projections are expected to affect the groundwater resources of the Mediterranean hydrological basins. This work focuses on the Viannos alluvial basin at the island of Crete, Greece. It considers primarily the increasing water demands for irrigation in the area of interest and the projected precipitation trend in the next five hydrological years for the island of Crete. The groundwater system is simulated based on the current hydrological/hydrogeological conditions of the basin and based on anticipated hydrological events. Scenarios concerning future precipitation trends and pumping schemes at existing wells are examined to assess the near-future stresses on the basin groundwater resources. Groundwater flow modeling is performed using the Visual Modflow software. Based on the study of different scenarios modeling results show that the aquifer is primarily affected during the dry period of the hydrological year. However, sufficiently replenishment is observed during the wet period as the highest water table drop is 0.65 m at the end of the 5 years modelling period. Therefore, the aquifer is not expected to face serious problems in the near future from the increased irrigation demands and from the short-term projected precipitation trends. Simulations for 10 and 20-year periods following the precipitation projections and the specified pumping schemes also show that the aquifer resources are not expected to be significantly affected.

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The study and management of the groundwater resources of a large, deep, coastal, karstic aquifer represent a very complex hydrogeological problem. Here, this problem is successfully approached by using an equivalent porous continuous medium (EPCM) to represent a karstic Apulian aquifer (southern Italy). This aquifer, which is located on a peninsula and extends to hundreds of metres depth, is the sole local source of high-quality water resources. These resources are at risk due to overexploitation, climate change and seawater intrusion. The model was based on MODFLOW and SEAWAT codes. Piezometric and salinity variations from 1930 to 2060 were simulated under three past scenarios (up to 1999) and three future scenarios that consider climate change, different types of discharge, and changes in sea level and salinity. The model was validated using surveyed piezometric and salinity data. An evident piezometric drop was confirmed for the past period (until 1999); a similar dramatic drop appears to be likely in the future. The lateral intrusion and upconing effects of seawater intrusion were non-negligible in the past and will be considerable in the future. All phenomena considered here, including sea level and sea salinity, showed non-negligible effects on coastal groundwater.

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The groundwater is the only source of availability of fresh water in tiny coral islands. In the past decades, there has been growing demand for fresh water to meet the need of domestic besides other purposes. The aquifer system on these islands is fragile besides being subjected to various stresses like high subsurface discharge, increased abstraction, improper disposal of waste water and tidal waves of ocean all of which subject the aquifer prone to sea water intrusion and thus reduction and deterioration the water quality. Therefore, understanding the aquifer's behavior and then work out a sustainable option for fresh water is essential. The paper concerns optimizing of pumping and artificial recharge paces to reduce the effects of various stresses over tiny and fragile lens-shaped coral island aquifer system. The density driven ground water flow was simulated using SEAWAT (MODFLOW and MT3D based computer program) model. Detailed hydrogeological investigations were carried out to determine the quantity of freshwater that could be pumped to avoid the seawater intrusion into the aquifer through modeling. Initial heads, physical parameters and boundary conditions of the study area have been defined in the model based on field data, geophysical measurements and interpretations and hydrogeological studies. The model was calibrated by obtaining a match of computed and observed values of the water table, as hydraulic head is much more sensitive to pumping rates than any other stress. A few sentences about: flow model were utilized to derive optimal pumping rate; the effect of artificial recharge through the model, has also proved that the salt-water intrusion could be stopped by raising the water level through temporarily storing the artificially recharged water post construction of subsurface dam near the coast. (C) 2011 Elsevier Ltd. All rights reserved.

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Quantifying recharge from agricultural areas is important to sustain long-term groundwater use, make intelligent groundwater allocation decisions, and develop on-farm water management strategies. The scarcity of data in many arid regions, especially in the Middle East, has necessitated the use of combined mathematical models and field observations to estimate groundwater recharge. This study was designed to assess the recharge contribution to groundwater from rainfall and irrigation return flow in the Mosian plain, west of Iran. The Inverse modeling approach and remote sensing technology (RS) were used to quantify the groundwater recharge. The recharge for steady-state conditions was estimated using the Recharge Package of MODFLOW. The land-use map for the research area was produced using remote sensing and satellite images technology. According to results, groundwater recharge from the rainfall and irrigation return flow was at the rate of 0.15 mm/day. The recharge to the groundwater from rainfall was about 0.08 mm/day (10.8 % of total rainfall). The average of groundwater recharge contribution in the study area was about 0.39 mm/day that include 15.2 % of the total water used in the irrigated fields. We can conclude that irrigation water is the most important resource of groundwater recharge in this area, consequently, it should be integrated into relevant hydrological models as the main source of groundwater recharge.

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This study was carried out to examine the impact of an artificial recharge site on groundwater level and salinity using treated domestic wastewater for the Korba aquifer (north eastern Tunisia). The site is located in a semi-arid region affected by seawater intrusion, inducing an increase in groundwater salinity. Investigation of the subsurface enabled the identification of suitable areas for aquifer recharge mainly composed of sand formations. Groundwater flow and solute transport models (MODFLOW and MT3DMS) were then setup and calibrated for steady and transient states from 1971 to 2005 and used to assess the impact of the artificial recharge site. Results showed that artificial recharge, with a rate of 1500 m(3)/day and a salinity of 3.3 g/L, could produce a recovery in groundwater level by up to 2.7 m and a reduction in groundwater salinity by as much as 5.7 g/L over an extended simulation period. Groundwater monitoring for 2007-2014, used for model validation, allowed one to confirm that the effective recharge, reaching the water table, is less than the planned values.

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The water resources are exhausted by the increasing demand related to the population growth. They are also affected by climate circumstances, especially in arid and semi-arid regions. These areas are already undergoing noticeable shortages and low annual precipitation rate. This paper presents a numerical model of the Sfax shallow aquifer system that was developed by coupling the geographical information system tool ArcGIS 9.3 and ground water modeling system GMS6.5's interface, ground water flow modeling MODFLOW 2000. Being in coastal city and having an arid climate with high consumption rates, this aquifer is undergoing a hydraulic stress situation. Therefore, the groundwater piezometric variations were calibrated for the period 2003-2013 and simulated based on two scenarios; first the constant and growing consumption and second the rainfall forecast as a result of climate change scenario released by the Tunisian Ministry of Agriculture and Water Resources and the German International Cooperation Agency "GIZ" using HadCM3 as a general circulation model. The piezometric simulations globally forecast a decrease that is about 0.5 m in 2020 and 1 m in 2050 locally the decrease is more pronounced in "Chaffar" and "Djbeniana" regions and that is more evident for the increasing consumption scenario. The two scenarios announce a quantitative degradation of the groundwater by the year 2050 with an alarming marine intrusion in "Djbeniana" region. (C) 2018 Elsevier Ltd. All rights reserved.

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Despite being a biodiversity hotspot, the Mahanadi delta is facing groundwater salinization as one of the main environmental threats in the recent past. Hence, this study attempts to understand the dynamics of groundwater and its sustainable management options through numerical simulation in the Jagatsinghpur deltaic region. The result shows that groundwater in the study area is extensively abstracted for agricultural activities, which also causes the depletion of groundwater levels. The hydraulic head value varies from 0.7 to 15 m above mean sea level (MSL) with an average head of 6 m in this low-lying coastal region. The horizontal hydraulic conductivity and the specific yield values in the area are found to vary from 40 to 45 m/day and 0.05 to 0.07, respectively. The study area has been calibrated for two years (2004-2005) by using these parameters, followed by the validation of four years (2006-2009). The calibrated numerical model is used to evaluate the net recharge and groundwater balance in this study area. The interaction between the river and coastal unconfined aquifer system responds differently in different seasons. The net groundwater recharge to the coastal aquifer has been estimated and varies from 247.89 to 262.63 million cubic meters (MCM) in the year 2006-2007. The model further indicates a net outflow of 8.92-9.64 MCM of groundwater into the Bay of Bengal. Further, the outflow to the sea is preventing the seawater ingress into the shallow coastal aquifer system.

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Mujib watershed is an important groundwater basin which is considered a major source for drinking and irrigation water in Jordan. Increased dependence on groundwater needs improved aquifer management with respect to understanding deeply recharge and discharge issues, planning rates withdrawal, and facing water quality problems arising from industrial and agricultural contamination. The efficient management of this source depends on reliable estimates of the recharge to groundwater and is needed in order to protect Mujib basin from depletion. Artificial groundwater recharge was investigated in this study as one of the important options to face water scarcity and to improve groundwater storage in the aquifer. A groundwater model based on the MODFLOW program, calibrated under both steady- and unsteady-state conditions, was used to investigate different groundwater management scenarios that aim at protecting the Mujib basin. The scenarios include variations of abstraction levels combined with different artificial groundwater recharge quantities. The possibilities of artificial groundwater recharge from existing and proposed dams as well as reclaimed municipal wastewater were investigated. Artificial recharge options considered in this study are mainly through injecting water directly to the aquifer and through infiltration from reservoir. Three scenarios were performed to predict the aquifer system response under different artificial recharge options (low, moderate, and high) which then compared with no action (recharge) scenario. The best scenario that provides a good recovery for the groundwater table and that can be feasible is founded to be by reducing current abstraction rates by 20% and implementing the moderate artificial recharge rates of 26 million(M)m(3)/year. The model constructed in this study helps decision makers and planners in selecting optimum management schemes suitable for such arid and semi-arid regions.

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Recently, many studies have investigated the effect of climate change on groundwater resources in semiarid and arid areas and have shown adverse effects on groundwater recharge and water level. However, only a few studies have shown suitable strategies for reducing these adverse effects. In this study, climate conditions were predicted for the future period of 2020-2044, under the emission scenarios of RCP2.6, RCP4.5, and RCP8.5, for Isfahan-Borkhar aquifer, Isfahan, Iran, using MODFLOW-2000 (MODFLOW is United States Geological Survey product). Results showed that the average groundwater level of the aquifer would decrease to 13, 15, and 16 m in 2012 to 2044 approximately under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively. Then, three groundwater sustainability management scenarios were defined that included 10%, 30%, and 50% reduction in groundwater extraction. These strategies simulated the reduced negative effects of climate change on the aquifer. The results showed that decreases in water withdrawal rates of 10%, 30%, and 50% under RCP8.5 scenario (critical scenario) could decrease the mean groundwater level by 14, 11, and 7 m, respectively. The main result of the study showed that 50% reduction in groundwater withdrawal may increase the groundwater levels significantly in order to restore the aquifer sustainability in the study area. In this study, with assuming that the current harvest of wells in the future period is constant, so the results of studies showed that for the aquifer's sustainability management, the water abstraction from the aquifer should reduce up to 50% of the existing wells. Changing the irrigation method from surface to subdroplet irrigation plays an important role in reducing the withdrawal from the aquifer. The results of a study in Iran have shown that the change in the irrigation method from surface to subdroplet irrigation causes a 40% reduction in water use for agriculture.

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Overlapping and adjacent ground water investigations are common in areas where aquifers are threatened by industrial development. In the Indianapolis area in Marion County, Indiana, a patchwork of ground water flow models have been used during the past 20 years to evaluate ground water resources and to determine the effects of local contamination. In every case these ground water models were constructed from scratch. Site specific finite difference grids or finite element meshes inhibit the direct reuse of input data when the area of interest shifts. Because the aquifer is not discretized into a grid or mesh with analytic element models, there are unique opportunities for direct reuse of model input data. In two applications of this principle we illustrate how the newly emerging analytic element method allows a fairly straightforward reuse of model input data from previous models in the same general area. In analytic element models of Central Indiana, streams and their tributaries are represented in different resolutions. Input data items of several modeling studies are stored and cataloged on disk in such a manner that they can be selectively retrieved by a data management program PREPRO. In this manner, a new ground water model can be set up quickly with input data which have been previously defined and tested during model calibration.

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Shallow renewable groundwater sources have been used to satisfy the domestic needs and the irrigation in many parts of Saudi Arabia. Increased demand for water resulting from accelerated development activities has placed excess stress on the renewable sources especially in coastal aquifers of the western region of Saudi Arabia. It is expected that the current and future development activities will increase the rate of groundwater mining of the coastal aquifer near the major city Jeddah and surrounding communities unless management measures are implemented. The current groundwater development of Dahaban coastal aquifer located at alluvial fan at the confluence of three major Wadis is depleting the shallow renewable groundwater sources and causes deterioration of its quality. Numerical models are known tools to evaluate groundwater management scenarios under a variety of development options under different hydrogeological regimes. In this study, two models are applied-the MODFLOW for evaluating the hydrodynamic behaviors of the aquifer and MT3D salinity distribution to the costal aquifer near Dahaban town. The models' simulation evaluates two development scenarios-the impact of excessive abstraction and the water salinity variation keeping abstraction at its current or increases in levels with or without groundwater recharge taking place. The simulation evaluated two scenarios covering a 25-year period-keeping the current abstraction at its current and the other scenario is increasing the well abstraction by 50% for dry condition (no recharge) and wet condition (with recharge). The analysis reveals that, under the first scenario, the continuation of the current pumping rates will result in depletion of the aquifer resulting in drying of many wells and quality deterioration at the level of 2,500 ppm. The results are associated with the corresponding salinity distribution in the region. Simulation of salinity in the region is a density-independent problem as salt concentration does not exceed 2,000 ppm, which is little value compared with sea salinity that amounts to 40,000 ppm. It is not recommended to increase the pumping rate than the current values. However, for the purpose of increasing water resources in the region, it is recommended to install new wells in virgin zones west of Dahaban main road. Maps of high/low potential groundwater and maps of salinity zones (more or less than 1,000 ppm) are provided and could be used to identify zones of high groundwater potential for the four studied scenarios. The implemented numerical simulation of Dahaban aquifer was undertaken to assess the water resources potential in order to reduce the depletion of sources in the future.

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In Argentina, the complementary irrigation has increased in most agricultural regions, where it is necessary to minimize possible negative impacts on the quantity and quality of groundwater. Numerical modeling techniques are used to obtain projections of the aquifer dynamics, for which a conceptual model is needed that provides the input data in the numerical simulations. A hydrogeological conceptual model for a rural area of Buenos Aires Province (Argentina), where complementary irrigation has caused significant depletion of groundwater levels during the irrigation season, has been developed. It was based on available geophysical and hydrogeological information and measurements of piezometric levels and hydraulic parameters of the aquifer together with the geochemical analysis of groundwater. This model was imported to a numerical model and the hydrogeological parameters were adjusted by the calibration with static piezometric levels measured in the wells. The conceptual model was validated satisfactorily using a fitting criterion to reach a value of root mean square error less than 5%. Different simulations of the probable drawdowns of the levels due to pumping were performed in the study area. The main hydrogeological unit is semi-confined, mostly comprising of a multilayer unit with good quality of water. Its minimum and maximum thickness was 60 and 240 m, respectively. The groundwater flows northwards from the hilly area to the plains. The recharge was 4.6 mm.year(-1), representing 5% of annual precipitation. Dynamic simulations show that the aquifer gets dried, which questions its sustainability. The alternating condition of the source or drain of the streams depends on the irrigation period or the dry season, respectively. Great drawdowns of piezometric levels in some areas might be the cause of changes in water classification. These results lead to the need of planning the use of groundwater as a complement to agricultural activity, considering sustainable employment of the resource.

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Climate change can have an adverse effect on agricultural productivity and water availability in semi-arid regions, as changes in surface water availability lead to groundwater depletion and resultant losses in crop yield. These inter-relationships necessitate an integrated management approach for surface water, groundwater, and crop yield as a holistic system. This study quantifies the future availability of surface water and groundwater and associated crop production in a large semi-arid agro-urban river basin in which agricultural irrigation is a leader consumer of water. The region of study is the South Platte River Basin (72,000 km(2)), Colorado, USA. The coupled SWAT-MODFLOW modeling code is used as the hydrologic simulator and forced with five different CMIP5 climate models downscaled by Multivariate Adaptive Constructed Analogs (MACA), each for two climate scenarios, RCP4.5, and RCP8.5, for 1980-2100. The hydrologic model accounts for surface runoff, soil lateral flow, groundwater flow, ground-water-surface water interactions, irrigation from surface water and groundwater, and crop yield on a per-field basis. In all climate models and emission scenarios, an increase of 3 to 5 degrees C in annual average temperature is projected. Whereas, variation in the projected precipitation depends on topography and distances from mountains. Based on the results of this study, the worst-case climate model in the basin is IPSL-CM5A-MR-8.5. Under this climate scenario, for a 1 degrees C increase in temperature and the 1.3% reduction in annual precipitation, the basin will experience an 8.5% decrease in stream discharge, 2-5% decline in groundwater storage, and 11% reduction in crop yield. These results indicate the significant effect of climate change on water and food resources of a large river basin, pointing to the need for immediate implementation of conservation practices. (C) 2021 Elsevier B.V. All rights reserved.

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Irrigation plays an important role in agricultural production, especially in arid and semi-arid regions. However, the conflict between water supply and demand will become more serious with increasing population. This study was to evaluate the effects of limited irrigation on regional-scale water movement and salt accumulation processes in agricultural areas. Due to frequent vertical interactions between the saturated groundwater zone and the unsaturated soil water zone and significant lateral groundwater movement between different horizontal areas in arid and semi-arid agricultural areas with shallow groundwater level, a quasi-three-dimensional (quasi-3D) model was adopted, which coupled one-dimensional (1D) soil water and salt movement and 3D groundwater and salt movement. The Yonglian irrigation area was used as the typical study site. Nine limited irrigation scenarios based on different allocations of irrigation water and hydrological years were set and analyzed. The main results were as follows: (1) The net groundwater recharge is negative under most of limited irrigation conditions, causing the decline of groundwater level ranging from 0.028 m to 0.199 m within one year. (2) With the decrease of irrigation and precipitation in farmland during the crop growth period, the groundwater recharge, groundwater recharge concentration, leaching efficiency coefficient will decrease linearly, while soil salt storage index will increase linearly. (3) Salts may accumulate in the root zone for dry years or normal years with autumn irrigation water less than 100 mm per unit area. (4) Lateral groundwater fluxes and salts contained in lateral groundwater fluxes will reduce approximately 30% and 40% under limited irrigation conditions. (5) The root zone will suffer from a very severe threat of soil salinization in farmlands in the future when considering the average annual increase rate of soil salt in the root zone is 3.6% under limited irrigation conditions, and necessarily intervenes are needed. The results could support decision-making for water-saving and soil salinity prevention in arid agricultural districts.

ABSTRACT:

In Iran, due to arid and semi-arid climate, groundwater resources play an essential role in food production, as well as domestic and industrial water supply. In recent years, increasing population, scarcity of surface water resources, and effects of worldwide and regional climate change have resulted in over-exploitation and unsustainability of these resources in the country. The present study aims to estimate groundwater sustainable yield, examine effects of spatial and temporal scale, and propose a plan for groundwater sustainable use in Nishapur Plain, in the north-east of Iran. In investigating the effects of spatial scale, the area of the plain is divided into several zones, with estimation of groundwater recharge and discharge for each zone and the temporal scale refers to the different time-scales used to estimate the average value of groundwater recharge and discharge. The results of the transient groundwater model of Nishapur Plain, revealed that average annual groundwater storage depletion is about 311 MGM(1) during the 8-year period of 2005-2013 with the minimum, average, and maximum water table decline of 0.6 m, 7.7 m and 11 m, respectively. The study results suggest that sustainable yield is closely correlated to the spatial and temporal scales, and refinement of spatial and temporal scales increases sustainable yield from 39 % to 59 % of the current pumping volume equal to about 100 MCM of water (or 8000 ha of irrigated land). Furthermore, when the groundwater withdrawals are limited to sustainable yield, increasing irrigation efficiency from 38 % (current efficiency) to about 60 %, can potentially result in maintaining irrigated areas and minimize adverse social and economic impacts of limiting groundwater usage. This is an achievable rate, based on data from the Iranian government organizations. The results of this study can be extended to other semi-arid agricultural areas, which primarily depend on groundwater.

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In this study, the applicability of the composite model for assessing seawater intrusion and soil salinization in coastal aquifers due to climate change was investigated. In this approach, flow in the saturated zone of a coastal aquifer is simulated using a three-dimensional saturated-unsaturated transport model and flow in the unsaturated zone between the surface and groundwater level is simulated using a one-dimensional model in the vertical direction. Long-term sea-level predictions obtained using the representative concentration pathway (RCP) 4.5 and 8.5 scenarios were applied for computing the sea-level rise for 91 country-managed reclaimed areas in the Republic of Korea. Composite results were obtained and analyzed for seawater intrusion and soil salinization due to sea-level rise. In the results of groundwater and soil salinity in all 91 reclaimed land, the increasing rate of groundwater and soil salinity in the RCP 4.5 scenario was 13.5% and 10.4%, respectively. In the RCP 8.5 scenario, the increasing rate of groundwater and soil salinity was 14.1% and 11.1%, respectively. The groundwater level increased to 0.41 m in the RCP 4.5 scenario and 0.51 m in the RCP 8.5 scenario. The results for two representative reclaimed land areas in the Heungwang and Deokchon districts were examined in detail. The composite analysis revealed that widespread damage could be caused by sea-level rise in the reclaimed land and that seawater intrusion in many regions will accelerate groundwater salinization over time. Moreover, the reclaimed land areas were characterized in terms of watershed size, presence of ponds, water levels of the ponds, and pond locations. In reclaimed land located in small watersheds, the groundwater recharge area was smaller than in land located in larger watershed areas. Consequently, the seawater in small watersheds penetrated further inland. Ponds with water levels higher than the sea level effectively prevented seawater intrusion into groundwater. If the water level of a pond is similar to or lower than the sea level, it indicates that seawater has already penetrated a large part of the aquifer. The composite model developed in this study seems to be one of the simulation methods that can be applied when simulating saturated and unsaturated zone to a large number of sites. Also, the study results could be used to establish and implement a long-term comprehensive plan for water resources at the national level, considering seawater intrusion due to climate change and providing a basis for establishing countermeasures against future seawater intrusion.

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Using available observed and digital data from the hydrogeological systems within the Berlin region, two regional numerical groundwater flow models were developed using a common methodology. These models encompass for the first time an entire area of about 1,300 km(2) of the groundwater flow system within the common sub-surface catchment area of the Berlin water works. The hydrogeological model and the model aquifers were developed using a unique approach from the available hydrogeological maps and sections of the Geological surveys from Berlin and Brandenburg. The numerical models were calibrated using equipotentials of the pumped aquifer for representative conditions of groundwater extraction as well as using hydraulic information. The models were applied to predict the groundwater yield of eleven water works for the Berlin government water agency.

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The Nebraska Sand Hills have a unique hydrologic system with very little runoff and thick aquifers that constantly supply water to rivers, lakes, and wetlands. A ground water flow model was developed to determine the interactions between ground water and streamflow and to simulate the changes in ground water systems by reduced precipitation. The numerical modeling method includes a water balance model for the vadose zone and MODFLOW for the saturated zone. The modeling results indicated that, between 1979 and 1990, 13 percent of the annual precipitation recharged to the aquifer and annual ground water loss by evapotranspiration (ET) was only about one-fourth of this recharge. Ground water discharge to rivers accounts for about 96 percent of the streamflow in the Dismal and Middle Loup rivers. When precipitation decreased by half the average amount of the 1979 to 1990 period, the average decline of water table over the study area was 0.89 m, and the streamflow was about 87 percent of the present rate. This decline of the water table results in significant reductions in ET directly from ground water and so a significant portion of the streamflow is maintained by capture of the salvaged ET.

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A three dimensional finite element model (FEFLOW) has been used for regional ground water flow modeling of Mihuaishun plain located in the south of Beijing, China. The numerical groundwater flow model is developed considering recharge components (precipitation infiltration, river leakage, and irrigation return flow). GIS interface is created for each source of recharge. Hydraulic conductivities and storage coefficient have been calibrated by the steady state model using the recorded data from 2007 to 2009. The model results is useful to identify the aquifer characteristics and to analyze the groundwater dynamics. The groundwater level monitoring network will be improved by analyzing groundwater levels. The future development scenarios are proposed to predict the trend changes of groundwater levels.

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To demonstrate the capabilities of Geographic Information System (GIS) techniques and numerical modeling for groundwater resources development in arid areas, specifically for the demarcation of suitable sites for the artificial recharge of groundwater aquifers, a study was carried out in the Maknassy basin, which is located in Central Tunisia. Thematic maps were prepared using a Hydrogeological Information System. All of the thematic layers were integrated using an ARCVIEW based model, enabling a map showing artificial recharge zones to be generated. Meanwhile, a ground water model, MODFLOW-2001, was used to estimate the effect of such water recharge on the piezometric behavior of the hydrological system. Additionally, these simulations helped manage ground water resources in the study area. The GIS-based demarcation of artificial zones developed in this study was based on logical conditions and reasoning, so that the same techniques, with appropriate modifications, could be adopted elsewhere, especially in similar aquifer systems in arid areas where the occurrence of groundwater is restricted and subject to a greater complexity. The efficiency of artificial recharge may be tested using hydrogeological modeling by simulating the effect of a potential groundwater refill. (C) 2010 Elsevier Ltd. All rights reserved.

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In the alpine basin of the Laubau, located south of Ruhpolding, a groundwater system connected to glacial gravels is characterized by groundwater level dynamics. Infiltration processes along streams which vary frequently in time and space, in combination with differentiated groundwater inflows from adjacent karstified and fractured hard rock, lead to frequent shifts in the groundwater level by more than 10 meters in the unconfined gravel aquifer. The hydrogeological context holds challenges for groundwater management and the design of water protection zones in this area. Accordingly, the hydrogeological-geohydraulic characteristics had to be carefully examined and quantified. The complex hydrogeological conceptual model is confirmed by a transient calibrated groundwater flow model that considers temporal and spatial variability of the infiltration rates of the streams as well as inflows from the adjacent hard rock.

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The unique characteristics of the hydrogeologic system of south Florida (flat topography, sandy soils, high water table, and highly developed canal system) cause significant interactions between ground water and surface water systems. Interaction processes involve infiltration, evapotranspiration (ET), runoff, and exchange of flow (seepage) between streams and aquifers. These interaction processes cannot be accurately simulated by either a surface water model or a ground water model alone because surface water models generally oversimplify ground water movement and ground water models generally oversimplify surface water movement. Estimates of the many components of flow between surface water and ground water (such as recharge and ET) made by the two types of models are often inconsistent. The inconsistencies are the result of differences in the calibration components and the model structures, and can affect the confidence level of the model application. In order to improve model results, a framework for developing a model which integrates a surface water model and a ground water model is presented. Dade County, Florida, is used as an example in developing the concepts of the integrated model. The conceptual model is based on the need to evaluate water supply management options involving the conjunctive use of surface water and groundwater, as well as the evaluation of the impacts of proposed wellfields. The mathematical structure of the integrated model is based on the South Florida Water Management Model (SFWMM) (MacVicar et al., 1984) and A Modular Three-Dimensional Finite-Difference Groundwater Flow Model (MODFLOW) (McDonald and Harbaugh, 1988).

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This paper emphasizes the supportive role of geostatistics in applying ground-water models. Field data of 1994 ground-water level, bedrock, and saltwater-freshwater interface elevations in south-central Kansas were collected and analyzed using the geostatistical approach. Ordinary kriging was adopted to estimate initial conditions for ground-water levels and topography of the Permian bedrock at the nodes of a finite difference grid used in a three-dimensional numerical model. Cokriging was used to estimate initial conditions for the saltwater-freshwater interface. An assessment of uncertainties in the estimated data is presented. The kriged and cokriged estimation variances were analyzed to evaluate the adequacy of data employed in the modeling. Although water levels and bedrock elevations are well described by spherical semivariogram models, additional data are required for better cokriging estimation of the interface data. The geostatistically analyzed data were employed in a numerical model of the Siefkes site in the project area. Results indicate that the computed chloride concentrations and ground-water drawdowns reproduced the observed data satisfactorily.

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The regulatory requirements for characterization of the Martinsville Alternative Site (MAS) were fulfilled by applying an iterative approach to the groundwater flow modeling of the site and surrounding area The approach consisted of field data collection and development of an initial conceptual model. The numerical model was then constructed to be consistent with the data and conceptual model. Next, the calibration results were evaluated statistically, and visually by a groundwater modeling review committee, to determine if the model accurately represented groundwater flow at the site. Initial results failed acceptance criteria because the values of numerical model input parameters had to be varied beyond observed data ranges to calibrate the results, and therefore the model was inconsistent with the initial conceptual model. This led to additional field data collection in areas where the numerical model deviated most from field-determined data. The new data provided sufficient information to revise the conceptual model and calibrate the numerical model successfully. Model calibration was followed by validation. Validation of the numerical model provided additional assurance that the model correctly simulated the observed system. No additional data were found to be necessary during validation of the MAS numerical model. The iterative approach proved to be successful for calibrating and validating this groundwater flow model and should be implemented from the onset of characterization planning in other applications.

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In three-dimensional (3-D) implicit geological modeling, the bounding surfaces between geological units are automatically constructed from lithological contact data (position and orientation) and the location and orientation of potential faults. This approach was applied to conceptualize a karst aquifer in the Middle Triassic Muschelkalk Formation in southwest Germany, using digital elevation data, geological maps, borehole logs, and geological interpretation. Dip and strike measurements as well as soil-gas surveys of mantel-borne CO(2)were conducted to verify the existence of an unmapped fault. Implicit geological modeling allowed the straightforward assessment of the geological framework and rapid updates with incoming data. Simultaneous 3-D visualizations of the sedimentary units, tectonic features, hydraulic heads, and tracer tests provided insights into the karst-system hydraulics and helped guide the formulation of the conceptual hydrogeological model. The 3-D geological model was automatically translated into a numerical single-continuum steady-state groundwater model that was calibrated to match measured hydraulic heads, spring discharge rates, and flow directions observed in tracer tests. This was possible only by introducing discrete karst conduits, which were implemented as high-conductivity features in the numerical model. The numerical groundwater flow model was applied to initially assess the risk from limestone quarrying to local water supply wells with the help of particle tracking.

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This study examines the groundwater characteristics in the Silver Bell Mountains, Arizona, USA, using a numerical model. Groundwater modeling is developed to describe the flow pattern in the study area and subsequently explores the possible interaction with regional porphyry copper deposits. A conceptual model is developed for the study area and regional hydrogeological conditions are simulated using the finite-difference groundwater flow model, MODFLOW-2005. The model results show that groundwater flow in the Silver Bell Mountains is strongly influenced by topography and its velocity varies with depth. In addition, the numerical model supports the idea of a continuous sustained interaction between groundwater flow and porphyry copper deposits in the Silver Bell Mountains. This interaction may result in continuing leaching of trace elements from the ore deposit, an important implication for continuing supergene alteration and enrichment of the porphyry copper deposit.

ABSTRACT:

An investigative study to determine the impact of a mining operation on local water resources over a 27 year period.

ABSTRACT:

Numerical groundwater modeling is an effective tool to guide water resources management and explore complex groundwater-dependent ecosystems in arid regions. In the Heihe River Basin (HRB), China's second largest inland river basin located in arid northwest China, a series of groundwater flow models have been developed for those purposes over the past 20 years. These models have elucidated the characteristics of groundwater flow systems and provided the scientific basis for a more sustainable management of groundwater resources and ecosystem services. The first part of this paper presents an overview of previous groundwater modeling studies and key lessons learned based on seven different groundwater models in the middle and lower HRB at sub-basin scales. The second part reviews the rationale for development of a regional basin-scale groundwater flow model that unifies previous sub-basin models. In addition, this paper discusses the opportunities and challenges in developing a regional groundwater flow model in an arid river basin such as the HRB.

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The feasibility of a hydrogeological modeling approach to simulate several thousand shallow groundwater-fed lakes and wetlands without explicitly considering their connection with groundwater is investigated at the regional scale (similar to 40,000 km(2)) through an application in the semi-arid Nebraska Sand Hills (NSH), USA. Hydraulic heads are compared to local land-surface elevations from a digital elevation model (DEM) within a geographic information system to assess locations of lakes and wetlands. The water bodies are inferred where hydraulic heads exceed, or are above a certain depth below, the land surface. Numbers of lakes and/or wetlands are determined via image cluster analysis applied to the same 30-m grid as the DEM after interpolating both simulated and estimated heads. The regional water-table map was used for groundwater model calibration, considering MODIS-based net groundwater recharge data. Resulting values of simulated total baseflow to interior streams are within 1% of observed values. Locations, areas, and numbers of simulated lakes and wetlands are compared with Landsat 2005 survey data and with areas of lakes from a 1979-1980 Landsat survey and the National Hydrography Dataset. This simplified process-based modeling approach avoids the need for field-based morphology or water-budget data from individual lakes or wetlands, or determination of lake-groundwater exchanges, yet it reproduces observed lake-wetland characteristics at regional groundwater management scales. A better understanding of the NSH hydrogeology is attained, and the approach shows promise for use in simulations of groundwater-fed lake and wetland characteristics in other large groundwater systems.

ABSTRACT:

A generalized water table fluctuation model based on precipitation was developed using a statistical conceptualization of unsaturated infiltration fluxes. A gamma distribution function was adopted as a transfer function due to its versatility in representing recharge rates with temporally dispersed infiltration fluxes, and a Laplace transformation was used to obtain an analytical solution. To prove the general applicability of the model, convergences with previous water table fluctuation models were shown as special cases. For validation, a few hypothetical cases were developed, where the applicability of the model to a wide range of unsaturated zone conditions was confirmed. For further validation, the model was applied to water table level estimations of three monitoring wells with considerably thick unsaturated zones on Jeju Island. The results show that the developed model represented the pattern of hydrographs from the two monitoring wells fairly well. The lag times from precipitation to recharge estimated from the developed system transfer function were found to agree with those from a conventional cross-correlation analysis. The developed model has the potential to be adopted for the hydraulic characterization of both saturated and unsaturated zones by being calibrated to actual data when extraneous and exogenous causes of water table fluctuation are limited. In addition, as it provides reference estimates, the model can be adopted as a tool for surveilling groundwater resources under hydraulically stressed conditions.

ABSTRACT:

Water resources in coastal areas can be profoundly influenced by both climate change and human activities. These climatic and human impacts are usually intertwined and difficult to isolate. This study developed an integrated model-based approach for detection and attribution of climatic and human impacts and applied this approach to the Luanhe Plain, a typical coastal area in northern China. An integrated surface water-groundwater model was developed for the study area using GSFLOW (coupled groundwater and surface-water flow). Model calibration and validation were performed for background years between 1975 and 2000. The variation in water resources between the 1980s and 1990s was then quantitatively attributed to climate variability, groundwater pumping and changes in upstream inflow. Climate scenarios for future years (2075-2100) were also developed by downscaling the projections in CMIP5. Potential water resource responses to climate change, as well as their uncertainty, were then investigated through integrated modeling. The study results demonstrated the feasibility and value of the integrated modeling-based analysis for water resource management in areas with complex surface water groundwater interaction. Specific findings for the Luanhe Plain included the following: (1) During the historical period, upstream inflow had the most significant impact on river outflow to the sea, followed by climate variability, whereas groundwater pumping was the least influential. (2) The increase in groundwater pumping had a dominant influence on the decline in groundwater change, followed by climate variability. (3) Synergetic and counteractive effects among different impacting factors, while identified, were not significant, which implied that the interaction among different factors was not very strong in this case. (4) It is highly probable that future climate change will accelerate groundwater depletion in the study area, implying that strict regulations for groundwater pumping are imperative for adaptation. (C) 2017 Elsevier B.V. All rights reserved.

ABSTRACT:

Climate and anthropogenic changes are expected to reduce renewable groundwater resources and to increase the risks of water scarcity, particularly in arid regions. Understanding current and future risks of water scarcity is vital to make the right water management decision at the right time. This study aims to analyze the impact of both human and climate pressures on groundwater availability in an arid environment: the Regueb basin in Central Tunisia. An integrated approach was used and applied at a monthly time step over a reference period (1976-2005) and a future period (2036-2065). Groundwater resources were assessed using hydrogeological modeling. Irrigation water withdrawals were evaluated based on remote sensing and the CropWat model. Urban water use was estimated from population growth and specific monthly water consumption data. The resulting values were used to compute two indicators (water stress index, groundwater balance) to evaluate water scarcity risks at the 2050 horizon. To assess current and future climate forcing on water resources, three climate scenarios were generated based on simulations from Coupled Model Intercomparison Project Phase 5 (CMIP5) data. A business-as-usual and an adaptation scenario (optimal cropping scenario) were performed by varying the surface areas and the crops grown in the irrigated area. Results show that the average annual water use will increase by 3.8 to 16.4% under climate change only, whereas it will increase by 100% under the business-as-usual scenario. Under the optimal cropping scenario, total water demand will increase by 50%. Water stress index indicates that under the climate change only scenario, water demand should be satisfied by the 2050 horizon, while under the other two scenarios, severe water stress will occur by 2050. The developed framework in this paper aims to fit in arid and semiarid regions in order to evaluate groundwater stress and to assess the efficiency of adaptation strategies. It results in two major recommendations regarding changes in land use and the improvement of groundwater monitoring.

ABSTRACT:

A comparative study on climate change and its impacts on coastal aquifers is performed for three Mediterranean areas. Common climate scenarios are developed for these areas using the ENSEMBLES projections that consider the A1b scenario. Temperature and precipitation data of three climate models are bias corrected with two different methods for a historic reference period, after which scenarios are created for 2020-2050 and 2069-2099 and used to calculate aquifer recharge for these periods based on two soil water budget methods. These multiple combinations of models and methods allow incorporating a level of uncertainty into the results. Groundwater flow models are developed for the three sites and then used to integrate future scenarios for three different parameters: (1) recharge, (2) crop water demand, and (3) sea level rise. Short-term predictions are marked by large ranges of predicted changes in recharge, only showing a consistent decrease at the Spanish site (mean 23 %), particularly due to a reduction in autumn rainfall. The latter is also expected to occur at the Portuguese site, resulting in a longer dry period. More frequent droughts are predicted at the Portuguese and Moroccan sites, but cannot be proven for the Spanish site. Toward the end of the century, results indicate a significant decrease (mean [25 %) in recharge in all areas, though most pronounced at the Portuguese site in absolute terms (mean 134 mm/year) and the Moroccan site in relative terms (mean 47 %). The models further predict a steady increase in crop water demand, causing 15-20 % additional evapotranspiration until 2100. Scenario modeling of groundwater flow shows its response to the predicted decreases in recharge and increases in pumping rates, with strongly reduced outflow into the coastal wetlands, whereas changes due to sea level rise are negligible.

ABSTRACT:

The groundwater resource contained within the sandy aquifers of the Swan Coastal Plain, south-west Western Australia, provides approximately 60 percent of the drinking water for the metropolitan population of Perth. Rainfall decline over the past three decades coupled with increasing water demand from a growing population has resulted in falling dam storage and groundwater levels. Projected future changes in climate across south-west Western Australia consistently show a decline in annual rainfall of between 5 and 15 percent. There is expected to be a reduction of diffuse recharge across the Swan Coastal Plain. This study aims to quantify the change in groundwater recharge in response to a range of future climate and land cover patterns across south-west Western Australia. Modelling the impact on the groundwater resource of potential climate change was achieved with a dynamically linked unsaturated/saturated groundwater model. A vertical flux manager was used in the unsaturated zone to estimate groundwater recharge using a variety of simple and complex models based on climate, land cover type (e. g. native trees, plantation, cropping, urban, wetland), soil type, and taking into account the groundwater depth. In the area centred on the city of Perth, Western Australia, the patterns of recharge change and groundwater level change are not consistent spatially, or consistently downward. In areas with land-use change, recharge rates have increased. Where rainfall has declined sufficiently, recharge rates are decreasing, and where compensating factors combine, there is little change to recharge. In the southwestern part of the study area, the patterns of groundwater recharge are dictated primarily by soil, geology and land cover. In the sand-dominated areas, there is little response to future climate change, because groundwater levels are shallow and much rainfall is rejected recharge. Where the combination of native vegetation and clayey surface soils restricts possible infiltration, recharge rates are very sensitive to reductions in rainfall. In the northern part of the study area, both climate and land cover strongly influence recharge rates. Recharge under native vegetation is minimal and is relatively higher where grazing and pasture systems have been introduced after clearing of native vegetation. In some areas, the recharge values can be reduced to almost zero, even under dryland agriculture, if the future climate becomes very dry.

ABSTRACT:

In recent years, extensive competition for groundwater use among different consumers has exploited major freshwater aquifers in Pakistan. There is an urgent need for appraisal of this precious resource followed by some mitigation strategies. This modelling study was conducted in the mixed cropping zone of the Punjab, Pakistan. Both remote sensing and secondary data were utilized to achieve objectives of this study. The data related to piezometric water levels, canal gauges, well logs, meteorological and lithological information were collected from Punjab Irrigation Department (PID), Water and Power Development Authority (WAPDA). Groundwater flow models for both steady and transient conditions were set-up using FEFLOW-3D. Water balance components and recharge were estimated using empirical relations and inverse modelling approaches. Both manual and automated approaches were utilized to calibrate the models. Moreover, sensitivity analysis was performed to see the response of model output against different model input parameters. Followed by calibration and validation, the model was run for different management scenarios, including lining of canal sections, minimization of field percolation, and change of groundwater abstraction. The study results show a drop in groundwater levels for almost all scenarios. The highest negative change was observed for the 4th scenario (i.e. 25% increase in groundwater pumping over a 10-year period), with a value of 3.73 m, by ignoring very wet summer and winter seasons. For normal weather conditions, the highest negative change was observed for the 4th scenario with a value of 2.91 m followed by 2.68 m for the 3rd scenario (i.e. 50% reduction in canal seepage and field percolation l over a 10-year period). For very wet summer and winter seasons, only one positive change was observed, for the 5th scenario (i.e. 25% decrease in groundwater pumping during 10 years period), with a value of 1.17 m. The changes for all other scenarios were negative. The mitigation strategy may include less groundwater pumping, by supporting cultivation of low delta crops and adjusting cropping patterns considering canal water supplies. It is further suggested to support current modelling results by incorporating more detailed information on cropping and by exploring the effect of climate change.

ABSTRACT:

Water resources, as the primary limiting factor, constrain the economic and social development in arid inland areas. The Zhangye Basin is a representative area of inland river basins, which is located in the middle parts of the Heihe River watershed, northwestern China. Facing with the huge water shortage, people exploited groundwater at a large scale in recent years. The reducing recharge from surface water and over-exploitation of groundwater led to the decline of groundwater levels and threatened the sustainability of water resources. This study constructed a conceptual and numerical groundwater flow model and calibrated the model based on the observed wells. A solute transport model was built using MT3DMS to calculate the groundwater age distribution in the Zhangye Basin. The simulated result shows that the youngest groundwater is distributed near the most upstream areas in the model domain, which is less than 1,000 a, older groundwater is distributed in deeper parts of the aquifer and near the discharge outlets, ranging from 6,000 a to over 20,000 a. Spatial variation of groundwater ages in the middle area indicates the recharge diversity between unconfined and confined aquifer. Groundwater age can serve as an indicator to evaluate groundwater's renewal capacity and sustainability. The formation of groundwater resources in the lower stream area would spend 10,000 a or even more than 20,000 a, so exploitation of groundwater in these areas should be restrained.

ABSTRACT:

The assessment of groundwater potential zones is crucial for estimating and managing available groundwater resources. In the proposed study, quantification of groundwater availability is performed using the information collected from the hydrogeological and geophysical (electrical resistivity) investigation of the aquifer. We delineate groundwater potential zones using a weighted overlay analysis based on the conventional method with 110 electrical resistivity surveys and 40 lithological data. MODFLOW is used to calibrate and validate the flow pattern and groundwater characteristics. The study area comprises a complex geological formation. The groundwater potential map is prepared using the observed groundwater level instead of rainfall data as the study area lacks rainfall stations. The final potential map is validated with the specific capacity obtained from the pumping test. This map is divided into 13 zones and each zone is considered as boundaries for the MODFLOW simulation. The thickness of each zone is assessed using the electrical resistivity method. The calibration and validation of the groundwater model are performed for one year and 1.5 years, respectively, between November 2012 and March 2015. We consider two layers, namely topsoil and unconfined/semi-confined aquifers in the groundwater model. During the calibration and validation periods, the groundwater volume is found to be 7.12 and 7.51 Mm(3), respectively. The groundwater mass balance assessment performed in this study will be helpful in the planning and management of groundwater resources in the area.

ABSTRACT:

Coastal aquifers have been identified as particularly vulnerable to impacts on water quantity and quality due to the high density of socio-economic activities and human assets in coastal regions and to the projected rising sea levels, contributing to the process of saltwater intrusion. This paper proposes a Regional Risk Assessment (RRA) methodology integrated with a chain of numerical models to evaluate potential climate change-related impacts on coastal aquifers and linked natural and human systems (i.e., wells, river, agricultural areas, lakes, forests and semi-natural environments). The RRA methodology employs Multi Criteria Decision Analysis methods and Geographic Information Systems functionalities to integrate heterogeneous spatial data on hazard, susceptibility and risk for saltwater intrusion and groundwater level variation. The proposed approach was applied on the Esino River basin (Italy) using future climate hazard scenarios based on a chain of climate, hydrological, hydraulic and groundwater system models running at different spatial scales. Models were forced with the IPCC SRES A1B emission scenario for the period 2071-2100 over four seasons (i.e., winter, spring, summer and autumn). Results indicate that in future seasons, climate change will cause few impacts on the lower Esino River valley. Groundwater level decrease will have limited effects: agricultural areas, forests and semi-natural environments will be at risk only in a region close to the coastline which covers less than 5% of the total surface of the considered receptors; less than 3.5% of the wells will be exposed in the worst scenario. Saltwater intrusion impact in future scenarios will be restricted to a narrow region close to the coastline (only few hundred meters), and thus it is expected to have very limited effects on the Esino coastal aquifer with no consequences on the considered natural and human systems. (C) 2015 Elsevier B.V. All rights reserved.

ABSTRACT:

In the multilayered aquifer system of North Aquitania in South-West France, the Oligocene and Eocene aquifers are pumped intensively for 50 years, mainly for domestic water. The huge pumping, which reaches 290 million m3 per year, causes a steady decline in groundwater levels. In particular, given the low recharge by rainfall, the Eocene confined aquifer collapsed with a water level decrease exceeding 30 m near the Bordeaux city. The resource is threatened, both in quantity, since the pumping exceeds the renewal and in quality, due to the reversal of flow gradients, with risk of brackish water invasion from the Gironde estuarine area in which the Eocene aquifer outcrops. The Oligocene is also subject to an increased vulnerability to surface pollution. A mathematical model simulating groundwater flows in this multilayer system has been implemented to quantify the water savings to be achieved, and simulate scenarios trend (population growth, industry and agriculture development) and combined scenarios (savings and substitutions). It is a regional multilayer water resources management model with 15 aquifer layers starting from the Plio-quaternaire aquifer at the top, down to the Bajocian aquifer at the bottom. The model, which has a spatial extension varying from 10,000 to 25,000 km(2) according of the aquifer, takes into account 67,000 square cells of size 2 km. It incorporates, at an annual time step, pumping in 3,250 wells and climatic data in five meteorological stations. It is calibrated in transient state using 380 observed time series of water level. The model was used to analyze the possibilities of restoring a balanced and safe state, using simulation of pumping scenarios. These simulations include scenarios incorporating trend forecasts of population growth, scenarios of economy needs, scenarios of pumping alternative aquifers and climate change scenarios. The climate change scenario selected is the moderate IPCC Arpege A1B scenario from Meteo - France.

ABSTRACT:

Groundwater plays a significant role in domestic, agricultural, and industrial water supply in semi-arid regions. In such areas, rapid growth of population and water demand in conjunction with climate change negatively impacts groundwater quantity and quality. In this research, human activities and climate change effects on groundwater quality in a semi-arid region was studied. First, a numerical groundwater model was calibrated as a tool for simulating an aquifer system. Then, groundwater salinity, as a measure of water quality, was simulated using the gene expression programming 'GEP' algorithm. In order to identify major factors influencing the salinity, the grey relational analysis (GR) technique was adopted. Furthermore, in the case study of Mahabad aquifer in northwestern Iran, decreasing precipitation has reduced river flow and aquifer recharge. Crop pattern change, through groundwater exploitation and irrigation return flow, impacted groundwater quality. Changes in temperature, evaporation and crop water requirement has also influenced the surface water-groundwater budget in the region. Groundwater simulations showed a decreasing trend in groundwater level while GEP analysis demonstrated that groundwater electrical conductivity (EC) increased over the past 40 years. Finally, GRA application showed that groundwater withdrawal and agricultural return flow had the highest correlation with increasing EC, compared with the effect of precipitation and temperature as climatic factors.

ABSTRACT:

Recently, groundwater resources in Egypt have become one of the important sources to meet human needs and activities, especially in coastal areas such as the western area of Port Said, where seawater desalination cannot be used due to the problem of oil spill and the reliance upon groundwater resources. Thus, the purpose of the study is the sustainable management of the groundwater resources in the coastal aquifer entailing groundwater abstraction. In this regard, the Visual MODFLOW and SEAWAT codes were used to simulate groundwater flow and seawater intrusion in the study area for 50 years (from 2018 to 2068) to predict the drawdown, as well as the salinity distribution due to the pumping of the wells on the groundwater coastal aquifer based on field investigation data and numerical modelling. Different well scenarios were used, such as the change in well abstraction rate, the different numbers of abstraction wells, the spacing between the abstraction wells and the change in screen depth in abstraction. The recommended scenarios were selected after comparing the predicted drawdown and salinity results for each scenario to minimize the seawater intrusion and preserve these resources from degradation.

ABSTRACT:

The Minqin Basin is at the lower reach of the Shiyang River of Gansu province in northwest China. Dramatic decline in groundwater level has resulted from over-abstraction of groundwater since the late 1950s to satisfy increasing irrigation and other demands. Severe water shortage led to environmental degradation. To better understand the spatial-temporal variation of groundwater levels and to evaluate the groundwater resources in the region, a three-dimensional regional groundwater flow model was built and calibrated under transient condition. The MODFLOW program was used and the research area was discretized as a square network with cell size of 400 x 400 m. The model showed that the aquifer was under destructive stress, with a groundwater resource deficit of 260 million cubic meters per year (Mm(3)/year) on average. Since the inflow of surface water from the upstream basin has declined to about 100-150 Mm(3)/year in recent decades, the irrigation return flow had become the main recharge and accounted for 60.6% of total recharge; meanwhile, abstraction by pumping wells took 99.2% from the total groundwater discharge.

ABSTRACT:

Increased groundwater extraction leads to the decrease of the extent of wetlands due to the implementation of a water-saving transformation project in an arid irrigation area. The application of integrated mitigation tools and strategies in China have increasing significance. In this study, an integrated approach (SWAT-MODFLOW) was followed; it is based on a soil and water assessment tool (SWAT) coupled with a modular three-dimensional finite difference groundwater model (MODFLOW). Recharge and evaporation values were estimated by SWAT and were then used to simulate groundwater in a MODFLOW model. Calibration (over the years 2000-2010) and validation (over the years 2010-2016) were performed, based on observed groundwater-level data; results showed that the combined SWAT-MODFLOW provides more accurate simulation and prediction of the dynamic changes of surface water and groundwater in irrigation areas than results from individual MODFLOW models. This method was applied to the Yanqi Basin, which is one of the most appropriate arid agricultural basins for modeling lake wetland and groundwater in China. The correlation coefficients (R-2) between the simulated and real groundwater level are 0.96 and 0.91 in SWAT-MODFLOW and MODFLOW, respectively. With the gradual increase in the extraction to 248%, 0.62 x 10(8) m(3) of groundwater discharged into the lake became -2.25 x 10(8) m(3). The lake level drops 1.3 m compared with the current year, when the groundwater exploitation increases by 10 x 10(8) m(3)/year. Overall, the results of the coupling model offer scientific evidence for agricultural water management and lake recovery, so as to enhance the water use coordination.

ABSTRACT:

Different scenarios of recharge and discharge were assessed for sustainable management of groundwater in Quaternary aquifer east of Nile Delta. MODFLOW was utilized to investigate the effect of land use change and damming construction in the upstream of the Nile River on the current and short-term groundwater management strategies. The interpretive transient simulation was performed between 2004 and 2016 after steady-state calibration in 2004, and transient state from 2004 to 2013 with different irrigation recharges associated with land use change in this period. Sensitivity analysis was performed for hydraulic conductivities, recharge, and conductance parameters. The predictive transient simulation was run till 2023 under three scenarios of increasing pumping rates by 15, 30, and 50% for agriculture expansion and specified head reduction of Port Said Canal by 0.2, 0.4, and 0.6 m associated with the reduction of Nile water levels after Grand Ethiopian Residence Dam, GERD operation in 2017. Results from the in- and out-flow budgets showed that groundwater aquifer is stable at the current rate of pumping till 2023. Groundwater heads decreased by 0.2 and 0.42 m in the southern section, and a slight increase in the northern part was noticed for the first and second scenarios, respectively. When additional pumping stress is applied (50% increase), groundwater head dropped by 0.66 m, and the storage is no longer able to maintain the aquifer capacity after 2020 (worst-case scenario).

ABSTRACT:

Stream flow, as a part of a basin hydrological cycle, will be sensible to water scarcity as a result of climate change. Stream vulnerability should then be evaluated as a key component of the basin water budget. Numerical flow modeling has been applied to an alluvial formation in a small mountain basin to evaluate the stream-aquifer relationship under these future scenarios. The Arbucies River basin (116 km(2)) is located in the Catalan Inner Basins (NE Spain) and its lower reach, which is related to an alluvial aquifer, usually becomes dry during the summer period. This study seeks to determine the origin of such discharge losses whether from natural stream leakage and/or induced capture due to groundwater withdrawal. Our goal is also investigating how discharge variations from the basin headwaters, representing potential effects of climate change, may affect stream flow, aquifer recharge, and finally environmental preservation and human supply. A numerical flow model of the alluvial aquifer, based on MODFLOW and especially in the STREAM routine, reproduced the flow system after the usual calibration. Results indicate that, in the average, stream flow provides more than 50% of the water inputs to the alluvial aquifer, being responsible for the amount of stored water resources and for satisfying groundwater exploitation for human needs. Detailed simulations using daily time-steps permit setting threshold values for the stream flow entering at the beginning of the studied area so surface discharge is maintained along the whole watercourse and ecological flow requirements are satisfied as well. The effects of predicted rainfall and temperature variations on the Arbucies River alluvial aquifer water balance are also discussed from the outcomes of the simulations. Finally, model results indicate the relevance of headwater discharge management under future climate scenarios to preserve downstream hydrological processes. They also point out that small mountain basins could be self-sufficient units so long as the response of the main hydrological components to external forces that produce water scarcity, as climate change or human pressures, is appropriately considered in water resource planning. (C) 2012 Elsevier B.V. All rights reserved.

ABSTRACT:

The presented modelling is a preliminary result that gives an overview of the groundwater budget in the Musi sub-basin. Results are consistent enough to give better monthly groundwater resource estimates that other global water balance methods such as Water Table Fluctuation. Results presented by this paper illustrate that at the sub-basin scale, groundwater modelling in a hard rock semi-arid context can be a well suited tool for estimating general groundwater resource evolution. Linking with inter-sectoral allocation models for building future management scenarios can be therefore considered.

ABSTRACT:

Dijil River catchment is a sub-catchment of the Abay drainage basin and covers 138.28 km(2). This paper presents numerical groundwater flow modeling at steady-state conditions, in a single-layer aquifer system under different stress or scenarios. A numerical groundwater flow models represent the simplification of complex natural systems, different parameters were assembled into a conceptual model to represent the complex natural system in a simplified form. The conceptual model was input into the numeric model to examine the system response. Based on geologic and hydrogeological information, confined subsurface flow condition was considered and simulated using MODFLOW 2000. The model calibration accounts matching of 24 observation points with the simulated head with a permissible residual head of +/- 10m. The sensitivity of the major parameters of the model was identified during the calibration process. According to the simulated water budget in the model, the simulated inflow is found to be 1.2791870E+05 m(3)/day which is nearly equal to the simulated outflow of 1.2791755E+05 m(3)/day with the difference being only 1.1484375E+00 m(3)/day. Water budget analysis reveals that outflow from river leakage accounts for 92.8 % of the total outflow and 14.1 % of the total inflow comes from the river leakage in the study area. Three scenarios of increased withdrawals and one scenario of altered recharge were used to study the system response. Accordingly, an increase in well withdrawal in scenario-I (existing wells pump simultaneously), scenario-II (existing drilled wells yield withdrawal increased by 30%), and scenario-III (additional eight wells having expected yield of 30 l/s drill and pump) resulted in an average decline of the steady-state water level by 1.06m, 1.68m, and 4.46m, respectively. They also caused the steady-state stream leakage to be reduced by about 2.93%, 4.58%, and 11.23%, and subsurface outflow by 9.41%, 14.67%, and 37.86%, respectively. A decrease in recharge by 25% and 50% results in a decrease of the head by 6.1m and 13.4m respectively, and a stream leakage decrease by 20.3%, and 40.3% respectively as compared to the simulated steady-state value. Therefore, adequate groundwater level monitoring wells should be placed in the catchment to control the total abstraction rates from the aquifer and fluctuations in groundwater levels.

ABSTRACT:

In coastal lowland plains, increased water demand on a limited water resource has resulted in declining groundwater levels, land subsidence and saltwater encroachment. In southwestern Kyushu, Japan, a sinking of the land surface due to over pumping of groundwater has long been recognized as a problem in the Shiroishi lowland plain. In this paper, an integrated model was established for the Shiroishi site using the modular finite difference groundwater flow model, MODFLOW, by McDonald and Harbaugh (1988) and the modular three-dimensional finite difference groundwater solute transport model, MT3D, by Zheng (1990) to simulate groundwater flow hydraulics, land subsidence, and solute transport in the alluvial lowland plain. Firstly, problems associated with these groundwater resources were discussed and then the established model was applied. The simulated results show that subsidence rapidly occurs throughout the area with the central prone in the center part of the plain. Moreover, seawater intrusion would be expected along the coast if the current rates of groundwater exploitation continue. Sensitivity analysis indicates that certain hydrogeologic parameters such as an inelastic storage coefficient of soil layers significantly contribute effects to both the rate and magnitude of consolidation. Monitoring the present salinization process is useful in determining possible threats to fresh groundwater supplies in the near future. In addition, the integrated numerical model is capable of simulating the regional trend of potentiometric levels, land subsidence and salt concentration. The study also suggests that during years of reduced surface-water availability, reduction of demand, increase in irrigation efficiency and the utilization of water exported from nearby basins are thought to be necessary for future development of the region to alleviate the effects due to pumping.

ABSTRACT:

In recent years, groundwater pumping has increased for domestic, industrial, and irrigation use in the Modjo River catchment. Understanding changes in groundwater levels is crucial for the sustainable use and management of aquifer. This study investigates the groundwater flow system and aquifer response to increased groundwater pumping and reduced recharge using the calibrated steady-state groundwater level and budget as a baseline. The groundwater flow corresponds to the direction of the Modjo River flow, following the topographic gradient. The simulated groundwater budget indicates that recharge from precipitation and surface water (crater lakes and river) are the main inflow to the aquifer, while the outflow from the aquifer is due to groundwater pumping, natural subsurface flow to downstream area, and base flow. Analysis of the different scenarios reveals that both an increase in well pumping and a decline in recharge resulted in a decrease of the base flow to Bishoftu crater lakes and Mojo River, and to the downstream subsurface flow. In conclusion, increasing human demand for groundwater and variability in recharge will affect groundwater contribution to surface water and ultimately will be a source of concern in the future for both environmental flows and groundwater management.

ABSTRACT:

Numerical groundwater models were used to assess groundwater sustainability on Jeju Island, South Korea, for various climate and groundwater withdrawal scenarios. Sustainability criteria included groundwater-level elevation, spring flows, and salinity. The latter was studied for the eastern sector of the island where saltwater intrusion is significant. Model results suggest that there is a need to revise the current estimate of sustainable yield of 1.77 x 10(6) m(3)/day. At the maximum extraction of 84 % of the sustainable yield, a 10-year drought scenario would decrease spring flows by 28 %, dry up 27 % of springs, and decrease hydraulic head by an island-wide average of 7 m. Head values are particularly sensitive to changes in recharge in the western parts of the island, due to the relatively low hydraulic conductivity of fractured volcanic aquifers and increased groundwater extraction for irrigation. Increases in salinity are highest under drought conditions around the current 2-m head contour line, with an estimated increase of up to 9 g/L under 100 % sustainable-yield use. The study lists recommendations towards improving the island's management of potable groundwater resources. However, results should be treated with caution given the available data limitations and the simplifying assumptions of the numerical modeling approaches.

ABSTRACT:

The likelihood of future global water shortages is increasing and further development of existing operational hydrologic models is needed to maintain sustainable development of the ecological environment and human health. In order to quantitatively describe the water balance factors and transformation relations, the objective of this article is to develop a distributed hydrologic model that is capable of simulating the surface water (SW) and groundwater (GW) in irrigation areas. The model can be used as a tool for evaluating the long-term effects of water resource management. By coupling the Soil and Water Assessment Tool (SWAT) and MODFLOW models, a comprehensive hydrological model integrating SW and GW is constructed. The hydrologic response units for the SWAT model are exchanged with cells in the MODFLOW model. Taking the Heihe River Basin as the study area, 10 years of historical data are used to conduct an extensive sensitivity analysis on model parameters. The developed model is run for a 40-year prediction period. The application of the developed coupling model shows that since the construction of the Heihe reservoir, the average GW level in the study area has declined by 6.05 m. The model can accurately simulate and predict the dynamic changes in SW and GW in the downstream irrigation area of Heihe River Basin and provide a scientific basis for water management in an irrigation district.

ABSTRACT:

Groundwater is an important resource for water use in the alluvial coastal lowland plain. In the Shiroishi lowland plain, southwestern Kyushu Island of Japan, land subsidence and salinity intrusion due to intense withdrawals of groundwater have become the main environmental issues for public concern. In this study, an integrated surface and groundwater model was established and applied to the Shiroishi site to simulate groundwater flow hydraulics, aquifer compaction and solute transport in the alluvial lowland plain. Moreover, a groundwater optimization model was also formulated to search for an optimal safe yield of groundwater extraction without violating salinity intrusion and other constraints. The simulated results show that groundwater levels in the aquifer greatly vary in response to varying climatic and pumping conditions. Consequently, land subsidence has rapidly occurred throughout the area with the central prone in Shiroishi basin. As a result of pumping and land subsidence, seawater has been intruded along the coast. in case of relative sea level rise, seawater intrusion appears to extend much farther in land from the coast. From the viewpoint of agricultural water management, pumping for irrigation with an optimal pumping amount that is a new finding from the optimization model will sustain groundwater quality in the study area. (c) 2006 Elsevier B.V. All rights reserved.

ABSTRACT:

The effect of climate change on future groundwater conditions in the Toyserkan basin in western Iran has been studied. In recent years, overexploitation for agricultural activities has led to water-table decline. Groundwater recharge rate predictions in the study area were obtained from the RCP4.5 Scenario of the 5th Assessment Report of the Intergovernmental Panel on Climate Change and HadGEM2 General Circulation Model. Outputs were downscaled with the RegCM4 Regional Climate Model coupled to the Community Land Model version 4.5 (CLM 4.5). RegCM4 model validation and prediction were attempted for 7 years (1999-2005) and 11 years (2015-2025), respectively. Validation results showed that RegCM4 reasonably simulated daily precipitation and monthly temperature and runoff. Firstly, geological, geophysical and hydrogeological data were used and evaluated to develop the conceptual model. Secondly, a 3D numerical model of groundwater flow was developed in order to describe the groundwater regime and predict the effects of water management strategies. Two scenarios were defined for the prediction period. The first scenario assumes that current exploitation rates will be continued, while the second one assumes a 20 percent decrease in pumping due to increased irrigation efficiency. The results showed a water-table rise from 2015 to 2025, which is heightened by increase in irrigation efficiency.

ABSTRACT:

Ground-water modeling is hindered, in general, by the lack of adequate information about the ground-water system and hence the need for an interactive and efficient system for data preparation and results analysis. Such a lack of information usually necessitates the use of a tedious iterative methodology within a sensitivity analysis scheme. This study facilitates modeling efforts by using the data-handling and graphical capabilities of a geographic information system in site-specific, numerical modeling of ground-water resources. Data for the island of Oahu, Hawaii, are given to illustrate the approach. The modeling procedure is integrated within the GIS as an item in the main menu. A USGS model, known as MOC, is linked into the system and applied to a case study to illustrate the procedure. The linkage is generic in nature and can be extended to other models as well. The availability of a programming language in the GIS package facilitates pre- and post-processing efforts within custom-made dialogue boxes and pull-down menus. On-line help screens for modeling as well as data handling can also be designed.

ABSTRACT:

Groundwater models are critical for simulating subsurface hydrological processes and guiding informed policymaking for groundwater management. However, the widely applied groundwater models typically use regularshaped grids to discretize aquifer systems and require that the directions of the grid edges are aligned with the hydraulic conductivity tensor. Such rigorous requirements for spatial discretization have constrained the models' application in aquifer systems with anisotropic hydrogeological characteristics. To address such limitations, we develop an improved groundwater flow model based on the multipoint flux approximation (MPFA) method in this study. The new model allows us to use arbitrary-shaped polygon grids to discretize aquifer systems and relaxes the rigorous requirement of the alliance between polygon edges and hydraulic conductivity tensor. The functionality and performance of the new model are demonstrated by comparing the output between our model, MODFLOW, and analytical solution in four case studies with various hydrogeological conditions. In a real-world watershed with complex-shaped boundaries, our model outperforms the conventional groundwater model in boundaries. The modeling results show that our model can yield accurate simulation of subsurface hydrological processes in aquifer systems with complex-shaped boundaries. Furthermore, our model can provide a more flexible discretization solution to couple surface water and groundwater model in integrated hydrological model development.

ABSTRACT:

Traditional numerical models usually use extensive observed hydraulic-head data as calibration targets. However, this calibration process is not applicable in remote areas with limited or no monitoring data. This study presents an approach to calibrate a large-scale groundwater flow model using the monthly Gravity Recovery and Climate Experiment (GRACE) satellite data, which have been available globally on a spatial grid of 1A degrees in the geographic coordinate system since 2002. A groundwater storage anomaly isolated from the terrestrial water storage (TWS) anomaly is converted into hydraulic head at the center of the grid, which is then used as observed data to calibrate a numerical model to estimate aquifer hydraulic conductivity. The aquifer system in the remote and hyperarid Qaidam Basin, China, is used as a case study to demonstrate the applicability of this approach. A groundwater model using FEFLOW is constructed for the Qaidam Basin and the GRACE-derived groundwater storage anomaly over the period 2003-2012 is included to calibrate the model, which is done using an automatic estimation method (PEST). The calibrated model is then run to output hydraulic heads at three sites where long-term hydraulic head data are available. The reasonably good fit between the calculated and observed hydraulic heads, together with the very similar groundwater storage anomalies from the numerical model and GRACE data, demonstrate that this approach is generally applicable in regions of groundwater data scarcity.

ABSTRACT:

A study was conducted to evaluate production strategies for a well field system near a source of groundwater contamination. Numerical modeling of groundwater flow was employed to generate hydraulic head configurations for different production scenarios. For a given scenario, an evaluation of contamination susceptibility was made by comparing head distributions in two aquifer units to the positions of the contaminant source and discharging water supply wells. The results of this study suggest that groundwater flow modeling can be a useful technique for planning the production of water supply wells in aquifers at risk of contamination from anthropogenic pollution sources.

ABSTRACT:

In data-sparse areas, due to the lack of hydrogeological data, numerical groundwater models have some uncertainties. In this paper, a nested model and a multi-index calibration method are used to improve the reliability of a numerical groundwater model in a data-sparse region, the Nalinggele River catchment in the Qaidam Basin. Referencing this key study area, a regional three-dimensional groundwater flow model is developed in a relatively complete hydrogeological unit. A complex set of calibration indices, including groundwater fitting errors, dynamic groundwater trends, spring discharges, overflow zone location, and groundwater budget status, are proposed to calibrate the regional numerical groundwater model in the Nalinggele alluvial-proluvial fan. Constrained by regional groundwater modeling results, a local-scale groundwater model is developed, and the hydrogeological parameters are investigated to improve modeling accuracy and reliability in this data-sparse region.

ABSTRACT:

Accurate representation of artificial recharge is requisite to calibration of a ground water model of an unconfined aquifer for a semiarid or and site with a vadose zone that imparts significant attenuation of liquid transmission and substantial anthropogenic liquid discharges. Under such circumstances, artificial recharge occurs in response to liquid disposal to the vadose zone in areas that are small relative to the ground water model domain. Natural recharge, in contrast, is spatially variable and occurs over the entire upper boundary of a typical unconfined ground water model. An improved technique for partitioning artificial recharge from simulated total recharge for inclusion in a ground water model is presented. The improved technique is applied using data from the semiarid Hanford Site. From 1944 until the late 1980s, when Hanford's mission was the production of nuclear materials, the quantities of liquid discharged from production facilities to the ground vastly exceeded natural recharge. Nearly all hydraulic head data available for use in calibrating a ground water model at this site were collected during this period or later, when the aquifer was under the diminishing influence of the massive water disposals. The vadose zone is typically 80 to 90 in thick at the Central Plateau where most production facilities were located at this semiarid site, and its attenuation of liquid transmission to the aquifer can be significant. The new technique is shown to improve the representation of artificial recharge and thereby contribute to improvement in the calibration of a site-wide ground water model.

ABSTRACT:

A three-dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze the subsurface hydrodynamics in the basaltic terrain by giving particular emphasis to the well field that supplies domestic, agricultural, and industrial needs. The alluvial aquifer of the Ghatprabha River comprises shallow tertiary sediment deposits underlain by peninsular gneissic complex of Archean age, located in the central-eastern part of the Karnataka in southern India. Integrated hydrochemical, geophysical, and hydrogeological investigations have been helped in the conceptualization of groundwater flow model. Hydrochemical study has revealed that groundwater chemistry mainly controlled by silicate weathering in the study area. Higher concentration of TDS and NO3-N are observed, due to domestic, agriculture, and local anthropogenic activities are directed into the groundwater, which would have increased the concentration of the ions in the water. Groundwater flow model is calibrated using head observations from 23 wells. The calibrated model is used to forecast groundwater flow pattern, and anthropogenic contamination migration under different scenarios. The result indicates that the groundwater flows regionally towards the south of catchment area and the migration of contamination would be reached in the nearby well field in less than 10 years time. The findings of these studies are of strong relevance to addressing the groundwater pollution due to indiscriminate disposal practices of hazardous waste in areas located within the phreatic aquifer. This study has laid the foundation for developing detailed predictive groundwater model, which can be readily used for groundwater management practices.

ABSTRACT:

Groundwater models are vulnerable to uncertainties, especially those that are developed based on incomplete knowledge of the hydraulic parameters. Transmissivity is often the most uncertain parameter in groundwater modeling. This work evaluates the effect of the spatial variability of transmissivity on the outputs of the groundwater flow model of the Takelsa multilayer aquifer. The study was based on a combination of deterministic and stochastic modeling. Groundwater flow modeling and stochastic simulations were made using the PMWIN software (a version of MODFLOW). Initially, the groundwater flow model was developed in the steady state. The criteria used for the calibration process were based on the comparison between the observed and the simulated hydraulic level. Then, a stochastic approach was used and 100 simulations of transmissivity were performed. The simulated transmissivity values were used to recalculate the hydraulic head and the water budget of the Saouaf deep aquifer. Finally, the consequent 100 results obtained by running MODFLOW were analyzed. The results showed variations in the hydraulic head levels, but the flow direction remained the same. The impact of the spatial variability of transmissivity on the water budget shows a range of inflow and outflow rates of Saouaf aquifer, with special relevance to the sea intrusion which may cause a probable deterioration of the quality of the groundwater.

ABSTRACT:

Climate change and future abstraction regimes will influence the availability of groundwater resources. To alleviate any potential negative effects on aquifer systems and dependent industrial and human uses, it is important to develop long-term water management plans. This study evaluates the effect of climate change and future increased groundwater demand from a coastal aquifer located in Kwale County in southern Kenya. A previously calibrated numerical groundwater flow model has been used as an assessment tool to study how future climate (precipitation and temperature variation) and groundwater abstraction changes will affect the aquifer system. The groundwater flow model was built to simulate the period 2010 to 2017, and eight future model scenarios were developed that cover six hypothetical future years. Future groundwater abstraction has been based on current allocations and future estimates made by Kenya's Water Resources Authority. Future rainfall scenarios have been constructed based on a long historical data series (from 1959 to 2017) and the Standard Precipitation Index. The main results show that future abstraction increases due to economic growth exerts a minimum impact compared with expected climate variability. Recharge depends on intense rain events with important implications for both dry periods and for an average rainfall year. A succession of extended dry seasons may affect all water users. However, the groundwater level decline in the local shallow aquifer can reach five meters, with important consequences for local community water supplies. The most significant groundwater decline in drought periods is observed in the area surrounding the pumping wellfields in the deep aquifers, where the effects of drought and significant abstraction are multiplied. However, the effect of increased abstraction on the shallow aquifer system is limited. Despite groundwater level decline observed during prolonged dry periods, a dry period followed by a humid period leads to the relatively swift recovery of the groundwater system.

ABSTRACT:

Mediterranean areas are characterized by complex hydrogeological systems, where management of freshwater resources, mostly stored in karstic, coastal aquifers, is necessary and requires the application of numerical tools to detect and prevent deterioration of groundwater, mostly caused by overexploitation. In the Taranto area (southern Italy), the deep, karstic aquifer is the only source of freshwater and satisfies the main human activities. Preserving quantity and quality of this system through management policies is so necessary and such task can be addressed through modeling tools which take into account human impacts and the effects of climate changes. A variable-density flow model was developed with SEAWAT to depict the "current" status of the saltwater intrusion, namely the status simulated over an average hydrogeological year. Considering the goals of this analysis and the scale at which the model was built, the equivalent porous medium approach was adopted to represent the deep aquifer. The effects that different flow boundary conditions along the coast have on the transport model were assessed. Furthermore, salinity stratification occurs within a strip spteading between 4 km and 7 km from the coast in the deep aquifer. The model predicts,a similar phenomenon for some submarine freshwater springs and modeling outcomes were positively compared with measurements found in the literature. Two scenarios were simulated to assess the effects of decreased rainfall and increased pumping on saline intrusion. Major differences in the concentration field with respect to the "current" status were found where the hydraulic conductivity of the deep aquifer is higher and such differences are higher when Dirichlet flow boundary conditions are assigned. Furthermore, the Dirichlet boundary condition along the coast for transport modeling influences the concentration field in different scenarios at shallow depths; as such, concentration values simulated under stressed conditions are lower than those simulated under undisturbed conditions. (C) 2016 Elsevier B.V. All rights reserved.

ABSTRACT:

One of the most important issues for water resource management is developing strategies for groundwater modelling that are adaptable to data scarcity. These strategies are particularly important in arid and semi-arid areas where access to data is poor and data collection is difficult, such as the Lake Chad Basin in Africa. In the present study, we establish a numerical groundwater flow model and evaluate the effects of dry and wet periods on groundwater recharge in the Chari-Logone area (96 000 km(2)) of the Lake Chad Basin. Boundary conditions, flow direction, sources, and sinks for the Chari-Logone local model were obtained by revising and remodelling the Lake Chad Basin regional hydrogeological model (508 400 km(2)) developed by the BRGM (Bureau de Recherches Geologiques et Minieres) in the 1990s. The simulated aquifer water level showed good agreement with observed levels. Aquifer recharge is primarily determined by river-aquifer interactions and mostly occurs in the southern section of the study area. In wet years, groundwater recharge also occurs in the N'Djamena area. The approach we adopted provided relevant results and was useful as an initial step in more detailed modelling of the area. It also proved to be a useful method for groundwater modelling in large semi-arid and arid regions where available data are scarce. Copyright (C) 2013 John Wiley & Sons, Ltd.

ABSTRACT:

The Heihe River Basin (HRB) is an inland watershed in northwest China with a total area of approximately 130,000 km(2), stretching from the Qilian Mountains in the south to the oases and agricultural fields in the middle and further to the Gobi desert in the north bordering Mongolia. As part of a major ecohydrological research initiative to provide a stronger scientific underpinning for sustainable water management in arid ecosystems, a regional-scale integrated ecological and hydrological model is being developed, incorporating the knowledge based on the results of environmental isotope tracer analysis and the multiscale observation datasets. The first step in the model development effort is to construct and calibrate a groundwater flow model for the middle and lower HRB where the oases and vegetation along the Heihe river corridor are highly dependent on groundwater. In this study, the software tool Arc Hydro Groundwater' is used to build and visualize a hydrogeological data model for the HRB that links all relevant spatiotemporal hydrogeological data in a unified geodatabase within the ArcGIS environment. From the conceptual model, a regional-scale groundwater flow model has been developed using MODFLOW-2005. Critical considerations in developing the flow model include the representation of mountainous terrains and fluvial valleys by individual model layers, treatment of aquifer heterogeneities across multiple scales and selection of proper observation data and boundary conditions for model calibration. This paper discusses these issues in the context of the Heihe River Basin, but the results and insights from this study will have important implications for other large, regional groundwater modelling studies, especially in arid and semiarid inland river basins. Copyright (c) 2014 John Wiley & Sons, Ltd.

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Development of any numerical ground-water model is dependent on hydrogeologic data describing the subsurface. These data are obtained from geologic core analyses, stratigraphic analyses, aquifer performance tests, and geophysical studies. But typically in remote areas, these types of data are very sparse and site-specific in terms of the aerial extent of the resource to be modeled. Uncertainties exist as to how well the available data from a few locations defines a heterogeneous surficial aquifer such as the Biscayne Aquifer in Miami-Dade County, Florida. This is particularly the case when an exceptionally conductive horizontal flow zone is detected at one site due to specialized testing that was not historically conducted at the other at sites that provided data for the model. Not adequately accounting for the potential effect of the high flow zone in the aquifer within a ground-water numerical model, even though the zone may be of very limited thickness, might underpredict the well field protection capture boundaries. Applied Stochastic ground-water modeling in determining well field protection zones is steadily becoming important in addressing the uncertainty of the hydrogeologic subsurface parameters, specifically in karstic heterogeneous aquifers. This is particularly important in addressing the uncertainty of a 60-day travel time capture zone in the Northwest Well Field, Miami-Dade County, where a predominantly high flow zone controls much of the flow in the production wells. A stochastic ground-water modeling application along with combination of pilot points and regularization technique is presented to further consolidate the uncertainty of the subsurface.

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Malia's coastal aquifer supplies water for domestic and irrigation purposes most of northern part of Heraklion prefecture (central Crete). The extensive exploitation of groundwater since the late 1960s has resulted in a continual decline in groundwater level and significant degradation in groundwater quality, due to salinity intrusion in the coastal aquifer. Moreover, the aquifer will likely to experience impacts of climate-driven recharge changes in the coming years, with adverse consequences for water supply in the region. A regional groundwater flow model was developed to simulate the existing hydrogeological system, and to evaluate the effects of combined impacts of groundwater exploitation and climate variability in future. The investigation results suggest that the equivalent porous medium (EPM) regional scale, as it is capable to simulate the groundwater flow and the spreading of chloride concentration with sufficient accuracy. However, locally the transport of saline water may depend primarily on the karst conduit network rather than matrix permeability; therefore the point information must be evaluated and not taken as undisputed. Furthermore, the study provides a valuable guidance on predicting the seawater intrusion in aquifers under similar hydrogeological conditions; and offers a considerable issue in management of the groundwater quality deterioration.

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Seawater intrusion due to sea level rise and climate change could significantly contaminate coastal groundwater resources, particularly in Florida, the flat low-land state in the United States. Based on the field investigation and hydrological measurements, a three-dimensional SEAWAT model is developed to evaluate the groundwater flow cycling and seawater intrusion to freshwater system in the Woodville Karst Plain (WKP), a typical karst groundwater system in the Floridan aquifer. The karst conduit network in the aquifer acts as fast flow pathway for groundwater flow and solute transport, so seawater could deeply intrude into the aquifer. Wakulla Spring, an inland spring 17 km from the coast and a coastal submarine spring, Spring Creek Spring Complex are connected through the conduit network. The flow direction between the two springs switches under various rainfall conditions in this region, thus the discharges at two karst springs are used to estimate the location of seawater/freshwater mixing interface. The SEAWAT modeling results indicate that the mixing interface, defined as 2 PSU (Practical Salinity Unit), intrudes 3 to 5 km through the subsurface karst conduit during the dry season and severely contaminates nearly 1 km width of groundwater around the conduit. The salinity distribution and the distance of seawater intrusion through the conduit system are very sensitive to precipitation variation and the sea level boundary condition. Furthermore, predictions are made for seawater intrusion to the aquifer under various sea level rise, precipitation scenarios and water pumping. The results show that the seawater intrusion could reach and contaminate inland freshwater systems if sea level rises 1.0 m or during a long-term no-precipitation season. This study provides insights for modeling and predicting the vulnerability of a coastal karst aquifer through the simulation of variable-density flow.

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The hydrology of coastal catchments is influenced by both sea level and climate. Hence, a comprehensive assessment of the impact of climate change on coastal catchments is a challenging task. In the present study, a coupled groundwater-surface water model is forced by dynamically downscaled results from a general circulation model. The effects on water quantity and quality of a relatively large lake used for water supply are analyzed. Although stream inflow to the lake is predicted to decrease during summer, the storage capacity of the lake is found to provide a sufficient buffer to support sustainable water abstraction in the future. On the other hand, seawater intrusion into the stream is found to be a significant threat to the water quality of the lake, possibly limiting its use for water supply and impacting the aquatic environment. Additionally, the results indicate that the nutrient load to the lake and adjacent coastal waters is likely to increase significantly, which will increase eutrophication and have negative effects on the surface water ecology. The hydrological impact assessment is based on only one climate change projection; nevertheless, the range of changes generated by other climate models indicates that the predicted results are a plausible realization of climate change impacts. The problems identified here are expected to be relevant for many coastal regimes, where the hydrology is determined by the interaction between saline and fresh groundwater and surface water systems.

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Study region: Rib catchment in the Lake Tana sub-basin, Upper Blue Nile River, Ethiopia. Study focus: This paper aimed to assess the impacts of future increase in abstraction and recharge reduction on the groundwater, groundwater availability, and groundwater-surface waters interaction based on a three-dimensional groundwater flow modeling. Calibration was made under the steady state condition. Scenario analysis performed for 1) increase in abstraction, 2) decrease in recharge, 3) the worst-case scenario that combined the aforementioned two scenarios and with additional extraction for irrigation, and 4) for the optimal-case scenario, which considers 5% recharge increase for the worst-case scenario model. New hydrological insights for the region: It is found that the groundwater flows from uplands toward the Tana Lake. The total inflow to and outflow from the system in the calibrated model are 1733480 m(3)/d and 1840451 m(3)/d, respectively. Groundwater level drop, reduction in base flows to surface waters, and in evapotranspiration flux compared to the calibrated values encountered for all scenarios, which are significant (mean 38.4 m, 28.5-100 %, and 97.8 %, respectively) for the worst-case scenario. On the other hand, an increase in groundwater level (mean 9.8 m), base flows (0-14.4 %), and evapotranspiration flux (29.5 %) observed for the optimal scenario when compared to the worst-case scenario results. Results suggest that groundwater management measures should be implemented to mitigate the impacts.

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his paper considers the problem of integrating projected future climate change predictions into a catchment modelling framework to determine future impacts on the groundwater resource. Catchment hydrology will also be altered as land managers alter management and land use regimes in response to a changing climate.

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The demand for freshwater supplies is progressively ascending owing to the increase of the population expansion and economic growth. Available water resources have been reduced by pollution and over-pumping. Groundwater modeling is a powerful tool for water resources management, groundwater protection, and remediation. The aim of this study is to develop a numerical groundwater flow model for the Quaternary aquifer in Samalut city, Minia Governorate, Egypt. The model is used to determine the hydrogeological conditions of the aquifer, the flow directions as well as calculating the rates of recharge and discharge between surface water and groundwater in the study area. Furthermore, scenarios were designed in the model to assess the response of the aquifer to increase the groundwater extraction in the future. The model was calibrated by trial and error; simulated results were compared to the observed head and contour maps, which were generally in good agreement. No typical steady-state condition is prevailed in the aquifer and groundwater flow directions are toward northeast direction. The River Nile acts as a drain in the study area, while El-Ibrahimiya Canal and Bahr Yusef act as a source of aquifer recharge. The proposed scenarios showed that surface water plays an important role in recharging the aquifer during increasing groundwater extraction. The results showed that the change in the aquifer storage will be decreased from +48,125m(3)/day in the current state (2013) to +27,134m(3)/day and -869m(3)/day when the groundwater extraction is increased by 25% and 50%, respectively.

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Groundwater is a dynamic and replenishable natural resource. The numerical modeling techniques serve as a tool to assess the effect of artificial recharge from the water conservation structures and its response with the aquifers under different recharge conditions. The objective of the present study is to identify the suitable sites for artificial recharge structures to augment groundwater resources and assess its performance through the integrated approach of Geographic Information System (GIS) and numerical groundwater modeling techniques using MODFLOW software for the watershed located in the Kodaganar river basin, Dindigul district, Tamil Nadu. Thematic layers such as geology, geomorphology, soil, runoff, land use and slope were integrated to prepare the groundwater prospect and recharge site map. These potential zones were categorized as good (23%), moderate (54%), and poor (23%) zones with respect to the assigned weightage of different thematic layers. The major artificial recharge structures like percolation ponds and check dams were recommended based on the drainage morphology in the watershed. Finally, a threelayer groundwater flow model was developed. The model was calibrated in two stages, which involved steady and transient state condition. The transient calibration was carried out for the time period from January 1989 to December 2008. The groundwater model was validated after model calibration. The prediction scenario was carried out after the transient calibration for the time period of year up to 2013. The results show that there is 15 to 38% increase in groundwater quantity due to artificial recharge. The present study is useful to assess the effect of artificial recharge from the proposed artificial structures by integrating GIS and groundwater model together to arrive at reasonable results.

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Regional groundwater modelling studies in large semiarid regions are often hampered by field data scarcity, in both space and time. In such a case, remote sensing can offer complementary datasets and guide further investigations (e.g. Jackson 2002; Brunner et al. 2004; Schmid et al. 2005). Presented here is an example of how remote sensing and geographic information system (GIS) techniques have helped regional groundwater modelling through a better definition of groundwater recharge and discharge areas, groundwater/surface water interaction, and paleohydrological settings. The work focuses on the Quaternary unconfined aquifer covering 500,000 km2 in the central part of the Lake Chad Basin in north-central Africa. It is shared between Chad, Niger, Nigeria and Cameroon and provides fresh water for the majority of ?20 million inhabitants of the basin (Fig. 1). Quaternary sediments form a continuous layer made up of fluvio-lacustrine deposits and aeolian sands, isolated from underlying aquifers by a thick layer of Pliocene clay. The regional aridity may be illustrated by environmental conditions to the north of Lake Chad where the annual rainfall is lower than 200 mm and the population density does not exceed 0.05 inhabitants per km2. Previous reliable hydrogeological studies are few, most of them dealing with the southern half of the aquifer. Regional syntheses can be found, for instance, in Leblanc (2002) and Gaultier (2004). The Quaternary aquifer has large natural piezometric depressions, vast closed concentric sinks also called hollow aquifers. Major piezometric depressions have an amplitude of about 40 m and are found in SE Niger, central Chad, and NE Nigeria. The Quaternary aquifer interacts with the changing environment (climate, surface water and human activities). Understanding such a dynamic system and effective management of this vast groundwater resource underpins the need for a groundwater model of the Quaternary aquifer. Such a model requires good spatio-temporal definition of processes indicative of land surface and aquifer interactions.

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Changes in irrigation and land use may impact discharge of the Snake River Plain aquifer, which is a major contributor to flow of the Snake River in southern Idaho. The Snake River Basin planning and management model (SRBM) has been expanded to include the spatial distribution and temporal attenuation that occurs as aquifer stresses propagate through the aquifer to the river. The SRBM is a network flow model in which aquifer characteristics have been introduced through a matrix of response functions. The response functions were determined by independently simulating the effect of a unit stress in each cell of a finite difference groundwater flow model on six reaches of the Snake River. Cells were aggregated into 20 aquifer zones and average response functions for each river reach were included in the SRBM. This approach links many of the capabilities of surface and ground water flow models. Evaluation of an artificial recharge scenario approximately reproduced estimates made by direct simulation in a ground water flow model. The example demonstrated that the method can produce reasonable results but interpretation of the results can be biased if the simulation period is not of adequate duration.

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Uncertainty of groundwater model predictions has in the past mostly been related to uncertainty in the hydraulic parameters, whereas uncertainty in the geological structure has not been considered to the same extent. Recent developments in theoretical methods for quantifying geological uncertainty have made it possible to consider this factor in groundwater modeling. In this study we have applied the multiple-point geostatistical method (MPS) integrated in the Stanford Geostatistical Modeling Software (SGeMS) for exploring the impact of geological uncertainty on groundwater flow patterns for a site in Denmark. Realizations from the geostatistical model were used as input to a groundwater model developed from Modular three-dimensional finite-difference ground-water model (MODFLOW) within the Groundwater Modeling System (GMS) modeling environment. The uncertainty analysis was carried out in three scenarios involving simulation of groundwater head distribution and travel time. The first scenario implied 100 stochastic geological models all assigning the same hydraulic parameters for the same geological units. In the second scenario the same 100 geological models were subjected to model optimization, where the hydraulic parameters for each of them were estimated by calibration against observations of hydraulic head and stream discharge. In the third scenario each geological model was run with 216 randomized sets of parameters. The analysis documented that the uncertainty on the conceptual geological model was as significant as the uncertainty related to the embedded hydraulic parameters.

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This paper demonstrates that analytic element models have potential as powerful screening tools that can facilitate or improve calibration of more complicated finite-difference and finite-element models. We demonstrate how a two-dimensional analytic element model was used to identify errors in a complex three-dimensional finite difference model caused by incorrect specification of boundary conditions. An improved finite-difference model was developed using boundary conditions developed from a far-field analytic element model. Calibration of a revised finite-difference model was achieved using fewer zones of hydraulic conductivity and lake bed conductance than the original finite-difference model, Calibration statistics were also improved in that simulated base-flows were much closer to measured values. The improved calibration is due mainly to improved specification of the boundary conditions made possible by first solving the far-field problem with an analytic element model.

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Numerical models of ground-water flow within the regional aquifer underlying Lambton County, Ontario, Canada, are constructed by the conjunctive application of methods of regression and inverse analyses. Regression analysis of physiographic and hydraulic head data reveals a distinct relation between ground-water levels and ground-surface topography that is used to condition the aquifer models that are subjected to inverse analysis. Inverse analysis determines the variation of hydraulic head along the perimeter of the region and the distribution of ground-water recharge and discharge within the region that optimally replicate the observed hydraulic head data. The use of physiographic data as a substitute for geologic data in the construction of the aquifer models is defended on the basis of the constraints that apply to the investigation and the opportunity to invoke hydrogeologic judgment in the evaluation of the results. Interpretation of the results of the analyses reveals important characteristics of the hydrogeology of Lambton County, including an area of elevated groundwater recharge and the partitioning of ground-water discharge to the Saint Clair River.

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The groundwater pollution case at Mercier is a very complex one. Groundwater flow modeling has been a valuable tool in the assessment of this large environmental problem. However, due to the complexity of the hydrogeological setting, the modeling has been performed with various simple case models in lieu of a large complex model. Here we report the results of one of these piecewise modeling tasks that proved very useful in the explanation of the strong upward gradients observed in the bedrock aquifer. These results and their interpretation prove the usefulness of the piecewise modeling strategy in this case.

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Remotely-sensed elevation data are potentially useful for constructing regional scale groundwater models, particularly in regions where ground-based data are poor or sparse. Surface-water elevations measured by the Shuttle Radar Topography Mission (SRTM) were used to develop a regional-groundwater flow model by assuming that frozen surface waters reflect local hydraulic head (or groundwater potential). Drainage lakes (fed primarily by surface water) are designated as boundary conditions and seepage lakes and isolated wetlands (fed primarily by groundwater) are used as observation points to calibrate a numerical flow model of the 900 km(2) study area in the Northern Highland Lakes Region of Wisconsin, USA. Elevation data were utilized in a geographic information system (GIS) based groundwater-modeling package that employs the analytic element method (AEM). Calibration statistics indicate that lakes and wetlands had similar influence on the parameter estimation, suggesting that wetlands might be used as observations where open water elevations are unreliable or not available. Open water elevations are often difficult to resolve in radar interferometry because unfrozen water does not return off-nadir radar signals.

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A proposed horizontal well or radial collector well installation in shallow aquifers to enhance water withdrawal rates in Pintu Geng well field in Kelantan, Malaysia was simulated using the Drainage Package of MODFLOW groundwater model. The modelling exercise aimed at identifying an optimum pumping rate that would safely achieve the desired drawdown of less than 2 m in an area of 300 m radius surrounding the Pintu Geng horizontal collector well. The model also would serve as a basis for the design of the horizontal well components. High degree of grid refinement for the well location is needed to simulate the real field installation. However, for the purpose of designing water withdrawal systems, it is important to obtain the correct production rate of these wells for a given drawdown. A transient groundwater flow model was calibrated and validated with few assumptions of the horizontal well hydraulic properties. The model demonstrates that under natural flow condition at -3 m depth, the six collectors (drains) tap a volume of 19,200-43,700 m(3)/day. A steady-state model was also developed to predict the capture zone delineation. Attention is also given to the impact of the well installation to the surrounding 300 m radius by inspecting the degree of the drawdown.

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Mathematical groundwater modelling with homogeneous permeability zones has been used for decades to manage water resources in the Almonte-Marismas aquifer (southwest Spain). This is a highly heterogeneous detrital aquifer which supports valuable ecological systems in the Donana National Park. The present study demonstrates that it is possible to better characterize this heterogeneity by numerical discretization of the geophysical and lithological data available. We identified six hydrofacies whose spatial characteristics were quantified with indicator variogram modelling. Sequential Indicator Simulation then made it possible to construct a 3D geological model. Finally, this detailed model was included in MODFLOW through the Model Muse interface. This final process is still a challenge due to the difficulty of downscaling to a handy numerical modelling scale. New piezometric surfaces and water budgets were obtained. The classical model with zones and the model with 3D simulation were compared to confirm that, for management purposes, the effort of improving the geological heterogeneities is worthwhile. This paper also highlights the relevance of including subsurface heterogeneities within a real groundwater management model in the present global change scenario.

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Surface-water/groundwater exchange impacts water quality and budgets. In karst aquifers, these exchanges also play an important role in dissolution. Five years of river discharge data were analyzed and a transient groundwater flow model was developed to evaluate large-scale temporal and spatial variations of exchange between an 80-km stretch of the Suwannee River in north-central Florida (USA) and the karstic upper Floridan aquifer. The one-layer transient groundwater flow model was calibrated using groundwater levels from 59 monitoring wells, and fluxes were compared to the exchange calculated from discharge data. Both the numerical modeling and the discharge analysis suggest that the Suwannee River loses water under both low- and high-stage conditions. River losses appear greatest at the inside of a large meander, and the former river water may continue across the meander within the aquifer rather than return to the river. In addition, the numerical model calibration reveals that aquifer transmissivity is elevated within this large meander, which is consistent with enhanced dissolution due to river losses. The results show the importance of temporal and spatial variations in head gradients to exchange between streams and karst aquifers and dissolution of the aquifers.

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Flow-path and time-of-travel results for the Mojave River ground-water basin, southern California, calculated using the ground-water flow model MODFLOW and particle-tracking model MODPATH were similar to flow path and time-of-travel interpretations derived from delta-deuterium and carbon-14 data. Model and isotopic data both show short flow paths and young ground-water ages throughout the floodplain aquifer along most the Mojave River. Longer flow paths and older ground-water ages as great as 10,000 years before present were measured and simulated in the floodplain aquifer near the Mojave Valley. Model and isotopic data also show movement of water between the floodplain and regional aquifer and subsequent discharge of water from the river to dry lakes in some areas. It was not possible to simulate the isotopic composition of ground-water in the regional aquifer away from the front of the San Gabriel and San Bernardino Mountains-because recharge in these areas does not occur under the present-day climatic conditions used for calibration of the model. Published by Elsevier B.V.

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A three-dimensional groundwater flow model was used to evaluate the groundwater potential and assess the effects of groundwater withdrawal on the regional water level and flow direction in the central Beijing area. A program of groundwater modeling aimed at estimating current contaminant fluxes to the central area and site streams via groundwater was developed. The conceptual model developed for the site attempted to incorporate a complex stratigraphic profile in which groundwater flow and contaminant transport is strongly controlled by a shallow aquifer. Here, a conceptual model for groundwater flow and contaminant transport in central Beijing is presented. Model simulations indicated that a sharp drop in the hydraulic head occurs at the center of the model area, which generates a cone of depression and a continuous decline of head with respect to time as a result of heavy groundwater abstraction.

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In this work, an integrated methodology was developed to investigate hydrological processes in Zeramdine-Beni Hassen Miocene aquifer and to validate the groundwater proprieties deduced from the geological, geophysical, hydrodynamic and hydrochemical studies done in the region, using the coupling of groundwater flow model MODFLOW 2000 code with Geographic Information System tools. A 3-D groundwater flow model was developed for this aquifer using a large amount of available geological and hydrological data. The groundwater flow model was calibrated and validated with datasets during the 1980-2007 period. The results show that the ZBH aquifer exhibits the highest sensibility to changes of water infiltration and hydraulic conductivity. The model simulation shows a good degree of understand to the aquifer hydrogeology. The model can be regarded as a useful tool for analyzing the hydrological processes for complex groundwater that have similar geological and hydrogeological conditions and will help to propose a management rescue plan for the studied aquifer, especially for aquifer characterization in arid and semi arid regions. (C) 2012 Elsevier Ltd. All rights reserved.

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Despite the continuous increase in water supply from desalination plants in the Emirate of Abu Dhabi, groundwater remains the major source of fresh water satisfying domestic and agricultural demands. Groundwater has always been considered as a strategic water source towards groundwater security in the Emirate. Understanding the groundwater flow system, including identification of recharge and discharge areas, is a crucial step towards proper management of this precious source. One main tool to achieve such goal is a groundwater model development. As such, the main aim of this paper is to develop a regional groundwater flow model for the surficial aquifer in Abu Dhabi Emirate using MODFLOW. Up to our knowledge, this is the first regional numerical groundwater flow model for Abu Dhabi Emirate. After steady state and transient model calibration, several future scenarios of recharge and pumping are simulated. Results indicate that groundwater pumping remains several times higher than aquifer recharge from rainfall, which provides between 2 and 5% of total aquifer recharge. The largest contribution of recharge is due to subsurface inflow from the eastern Oman Mountains. While rainfall induced groundwater level fluctuation is absent in the western coastal region, it reaches a maximum of 0.5 m in the eastern part of the Emirate. In contrast, over the past decades, groundwater levels have declined annually by 0.5 m on average with local extremes spanning from 93 m of decline to 60 m of increase. Results also indicate that a further decrease in groundwater levels is expected in most of Emirate. At other few locations, upwelling of groundwater is expected due to a combination of reduced pumping and increased infiltration of water from nonconventional sources. Beyond results presented here, this regional groundwater model is expected to provide an effective tool to water resources managers in Abu Dhabi. It will help to accurately estimate sustainable extraction rates, assess groundwater availability, and identify pathways and velocity of groundwater flow as crucial information for identifying the best locations for artificial recharge.

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Numerical models are often used for simulating ground water flow. Written in state space form, the dimension of these models is of the order of the number of model cells and can be very high (> million). As a result, these models are computationally very demanding, especially if many different scenarios has to be simulated. Therefore we introduce in this paper a model reduction approach to develop an approximate model with a significantly reduced dimension. The reduction method is based upon several simulations of the large-scale numerical model. By computing the covariance matrix of the model results, we obtain insight into the variability of the model behavior. Moreover, selecting the leading eigenvector of this covariance matrix, we obtain the spatial patterns that represent the directions in state space where the model variability is dominant. These patterns are also called Emperical Orthogonal Functions (EOFs). The original numerical model can now be projected onto the reduced space spanned by the dominant spatial patterns. The result is a low dimensional model that is still able to reproduce the dominant model behavior. In this paper we introduce the reduction approach and describe a real life application of the appraoch to a large-scale numerical ground water flow model.

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The construction of 3D hydrogeological models for unconsolidated sedimentary aquifers remains particularly challenging, especially in Quaternary deposits. Simplifications at small or large scale are part of groundwater flow modeling and are often required due on the usual inherent complexity of the stratigraphic systems. This study analyzes the effects of hydrostratigraphic simplifications on the accuracy of 3D numerical groundwater flow models. Such investigation is conducted from an initial detailed model of an aquifer located in the Saguenay-Lac-St-Jean region in Canada and the considered simplifications are based on using the equivalent hydraulic conductivity concept. Different levels or approaches of simplification are applied to numerical simulated models and the results of the different scenarios are compared. A root mean square (RMS) calibration result of 3.79 m on the groundwater levels is obtained for the most detailed model, while the RMS ranges between 4.01 and 4.83 m with the simplified models. Such results illustrate a gain obtained in the calibration of the model with increasing level of hydrostratigraphic details, but that this gain is relatively limited. The proposed methodology for simplifying the hydrostratigraphic settings could be used by hydrogeological modellers for a wide variety of aquifers constituted of sedimentary granular material.

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The 1996 reauthorization of the Safe Drinking Water Act required that each state in the US addresses the protection of public drinking water sources, including the development and implementation of a source-water assessment program. Such a program includes delineating source-water assessment areas, inventorying potential contaminant sources within this area, and determining the water system's susceptibility to contamination. The public was also involved in various phases of the program. Hawaii's groundwater source assessment program is presented, along with an approach for implementation, which is consistent with federal requirements. The approach integrates groundwater models, aquifer databases, and a geographic information system. Source assessment areas were delineated by using numerical groundwater-flow models that used site-specific data to their fullest availability. The proposed approach is flexible enough to allow easy future updates as more sources are identified or as new information becomes available. The final product includes numerical scores that quantify the relative source susceptibility to contamination. Aquifer models developed in this study are potentially useful for future site-specific protection efforts or for other modeling purposes.

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Karst aquifers exhibit a dual flow system characterized by interacting conduit and matrix domains. This study evaluated the coupled continuum pipe-flow framework for modeling karst groundwater flow in the Madison aquifer of western South Dakota (USA). Coupled conduit and matrix flow was simulated within a regional finite-difference model over a 10-year transient period. An existing equivalent porous medium (EPM) model was modified to include major conduit networks whose locations were constrained by dye-tracing data and environmental tracer analysis. Model calibration data included measured hydraulic heads at observation wells and estimates of discharge at four karst springs. Relative to the EPM model, the match to observation well hydraulic heads was substantially improved with the addition of conduits. The inclusion of conduit flow allowed for a simpler hydraulic conductivity distribution in the matrix continuum. Two of the high-conductivity zones in the EPM model, which were required to indirectly simulate the effects of conduits, were eliminated from the new model. This work demonstrates the utility of the coupled continuum pipe-flow method and illustrates how karst aquifer model parameterization is dependent on the physical processes that are simulated.

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The mathematical development of a two-dimensional finite volume model for groundwater flow is described. Based on the hydraulic equations for saturated flow, the model deploys an improved least squares gradient reconstruction technique to evaluate the gradient at the control volume face, derived from the application of the finite volume formulation and using a cell-centred structured quadrilateral grid. The model has been compared to a finite difference model with orthogonal grids. The effects of grid non-orthogonality and skewness are investigated. The model was verified by comparison with analytical solutions and the results for a finite difference model. The finite volume model was then applied successfully to an aquifer discharging in a section of the River Tawe, UK, and the results were compared with results from MODFLOW and observed hydraulic heads. Results of the numerical model tests and field exercise showed that the use of finite volume method provides modellers with a consistent substitute for the finite difference methods with the same ease of use and an improved flexibility and accuracy in simulating irregular boundary geometries. (C) 2006 Elsevier Ltd. All rights reserved.

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In order to evaluate the groundwater resources and aquifer system of the Jilin urban area (JUA), a groundwater numerical flow model was established by using the groundwater modeling system based on data from 190 boreholes. River stages were interpolated to control the groundwater flow field. The input parameters such as hydraulic conductivity and specific yield were based on data from 260 pumping test data. The model was calibrated by trial and error, simulated results were compared to the observed head and contour maps, which were generally in good agreement, and the root mean squared error was 0.66 m. Sensitivity analysis was carried out and recharge proved to be the most sensitive factor in this model. The water budget showed that the input was 2.07x 10(8) m(3)/a, which was smaller than the output of 2.21 x 10(8) m(3)/a. A groundwater level decline and cone of depression exist in the Songhua and Aolong river valley. The JUA aquifer systems can be well and efficiently modeled by constructing a numerical model. Based on the supply and demand analysis of water resources, the established model would finally provide a scientific basis to use the groundwater resources sustainably in JUA.

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Numerical modeling of an aquifer is increasingly used as a power tool for monitoring and management of groundwater. This paper focuses on conceptualizing hydrogeological condition and establishing numerical simulation model using Visual MODFLOW to simulate the continuous depletion of groundwater in the southwestern part of the Soan watershed in Pakistan. An integrated groundwater modeling and management approach was adopted to provide suitable alternatives for water management in different hydro-environments. Geospatial techniques were employed for spatial database development, integration with a remote sensing (RS), and numerical groundwater flow modeling capabilities to simulate groundwater flow behavior. The calibration results indicated a reasonable agreement between the calculated and observed heads. The calibrated heads were used as initial conditions in the transientstate modeling. The modeling approach facilitated in identifying potential groundwater regime besides providing artificial recharge options for sustainable groundwater development.

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Groundwater flow modelling is an important technique which is used to study the dynamics of groundwater systems. Although, complex groundwater system with large set of parameters and associated uncertainty with those parameters makes modelling exercise difficult. In this study, development of groundwater model for Varanasi city and near around area was prompted to understand the groundwater dynamics and future groundwater resource scenarios in the region. The model was developed for the area of 2785 km(2), where aquifer thickness varied up-to 150 m. The model grid consisted of 210 rows and 210 columns with each cell size of 250 m x 250 m. To realize the different type of underground formations, model was built for five layers with recharge entering the aquifer from surface infiltration through the overlying confining unit and from seepage through riverbeds. The maximum part of the model domain is surrounded by the Ganga River, which was taken as a hydrologic boundary for the model. Model simulations were made to quantify groundwater flow within the alluvial aquifer as well as flow into and out of the system. The groundwater model was developed for the transient state condition for the year of 2006 to 2017. Several criteria were used during model development and calibration to determine how fine the model simulated conditions in the aquifer. Model calibration was done on the values of hydraulic conductivity and recharge rates. A root-mean-square error analysis was performed during calibration to serve as a criterion to minimize differences between observed and model computed water levels. Further, calibrated model was used to analyze different scenarios to understand the future scenario of water resources.

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Recent legislation required regional grassroots water resources planning across the entire state of Texas. The. Texas Water Development Board (TWDB), the state's primary water resource planning agency, divided the state into 16 planning regions. Each planning group developed plans to manage both ground water and surface water sources and to meet future demands of various combinations of domestic, agricultural, municipal, and industrial water consumers. This presentation describes the challenges in developing a ground water model for the Llano Estacado Regional Water Planning Group (LERWPG), whose region includes 21 counties in the Southern High Plains of Texas. While surface water is supplied to several cities in this region, the vast majority of the regional water use comes from the High Plains aquifer system, often locally referred to as the Ogallala Aquifer. Over 95% of the ground water demand is for irrigated agriculture. The LERWPG had to predict the impact of future TWDB-projected water demands, as provided by the TWDB, on the aquifer for the period 2000 to 2050. If detrimental impacts were noted, alternative management strategies must be proposed. While much effort was spent on evaluating the current status of the ground water reserves, an appropriate numerical model of the aquifer system was necessary to demonstrate future impacts of the predicted withdrawals as well as the effects of the alternative strategies. The modeling effort was completed in the summer of 2000. This presentation concentrates on the political, scientific, and nontechnical issues in this planning process that complicated the modeling effort. Uncertainties in data, most significantly in distribution and intensity of recharge and withdrawals, significantly impacted the calibration and predictive modeling efforts. Four predictive scenarios, including baseline projections, recurrence of the drought of record, precipitation enhancement, and reduced irrigation demand, were simulated to identify counties at risk of low final ground water storage volume or low levels of satisfied demand by 2050.

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Numerical groundwater flow modeling of Kohat basin : An example from Himalayan fold and thrust belt Pakistan

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Ground water flow modeling in a karst aquifer presents many difficulties. In particular, the hydrodynamic properties and the now behavior can vary over time. History matching of transient-state conditions is required to test the accuracy of the model under varying hydrodynamic conditions. The objective of this study was to illustrate how transient-state conditions can be used to history match a ground water flow model of a large aquifer, the La Rochefoucauld karst (Charente, France). The model used a porous medium equivalent and was based on a steady-state calibration of hydraulic conductivities. The history match consisted of studying the simulated heads and spring flow rates to test the capacity of the model to reproduce different aspects of the aquifer behavior, The simulated heads and flow rates were analyzed as new data using correlation and spectral analyses to compare the temporal structures of the measured and simulated time series. The analyses provided information on the storage capacity of the aquifer, the input-output delays, the degree of correlation between input and output, and the length of the impulse response of the aquifer, These data were used to study the impact of the hypotheses underlying the model (hydraulic conductivities, storage coefficient, representation of rivers, use of a porous medium equivalent). The results show that the model adequately simulates the overall behavior of the studied aquifer, The model can be used under variable hydrodynamic conditions to simulate ground water flow on a regional scale. This case study illustrates how a complete history match of a simplified representation of reality can lead to an adequate mathematical tool.

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The Manitou Mine sulphidic-tailings storage facility No. 2, near Val D'Or, Canada, was reclaimed in 2009 by elevating the water table and applying a monolayer cover made of tailings from nearby Goldex Mine. Previous studies showed that production of acid mine drainage can be controlled by lowering the oxygen flux through Manitou tailings with a water table maintained at the interface between the cover and reactive tailings. Simulations of different scenarios were performed using numerical hydrogeological modeling to evaluate the capacity of the reclamation works to maintain the phreatic surface at this interface. A large-scale numerical model was constructed and calibrated using 3 years of field measurements. This model reproduced the field measurements, including the existence of a western zone on the site where the phreatic level targeted is not always met during the summer. A sensitivity analysis was performed to assess the response of the model to varying saturated hydraulic conductivities, porosities, and grain-size distributions. Higher variations of the hydraulic heads, with respect to the calibrated scenario results, were observed when simulating a looser or coarser cover material. Long-term responses were simulated using: the normal climatic data, data for a normal climate with a 2-month dry spell, and a simplified climate-change case. Environmental quality targets were reached less frequently during summer for the dry spell simulation as well as for the simplified climate-change scenario. This study illustrates how numerical simulations can be used as a key tool to assess the eventual performance of various mine-site reclamation scenarios.

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The development and application of a digital computer model of the ground water reservoir of the island of Anholt is described. The model is based on a finite difference, two-dimensional approach. It was successfully used to investigate if the ground water at a planned well field might be polluted by sewage from nearby cesspools. Although the model is an approximation of the real aquifer conditions, the authors found the model very useful and suggest that modelling techniques be more widely used in ground water resource investigations.

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In this work, a 3D groundwater flow model integrating all important geological features of the hydrogeological system is developed to investigate hydrological processes in the Wadi Kafrein area of Jordan. A large amount of available geological and hydrological data is integrated to construct a 3D groundwater flow model for the Wadi Kafrein area. Using the newly developed mapping approach, the translation of the highly detailed geological formations to an unstructured finite element grids, can be accomplished with high precision. The existing data set for model calibration is scarce, which is a typical situation for many hydrogeological case studies. At first, the steady state calibration of the groundwater model is carried out based on the observation wells. Then, the time and space-dependent recharge from precipitation are applied at the top surface of the finite element model. The transient simulation is conducted during the period of 1996-2008 considering the abstraction rates of the production wells and discharge of the springs. The calculated water levels are close to the observed values. The difference is partly caused by return flows from irrigation and the groundwater inflow from the adjacent aquifers which are not taken into consideration so far. Since the Wadi Kafrein area is an important agricultural area in the semiarid region of the Lower Jordan Valley, the model developed in this study can be regarded as a useful tool for analyzing the hydrological processes and improving groundwater management practices elsewhere affected by similar geological and hydrogeological conditions.

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Ground water budget analysis in and basins is substantially aided by integrated use of numerical models and environmental isotopes. Spatial variability of recharge, storage of water of both modem and pluvial age, and complex three-dimensional flow processes in these basins provide challenges to the development of a good conceptual model. Ground water age dating and mixing analysis with isotopic tracers complement standard hydrogeologic data that are collected and processed as an initial step in the development and calibration of a numerical model. Environmental isotopes can confirm or refute a priori assumptions of ground water flow, such as the general assumption that natural recharge occurs primarily along mountains and mountain fronts. Isotopes also serve as powerful tools during postaudits of numerical models. Ground water models provide a means of developing ground water budgets for entire model domains or for smaller regions within the model domain. These ground water budgets can be used to evaluate the impacts of pumping and estimate the magnitude of capture in the form of induced recharge from streams, as well as quantify storage changes within the system. The coupled analyses of ground water budget analysis and isotope sampling and analysis provide a means to confirm, refute, or modify conceptual models of ground water flow.

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The Hangzhou Bay New Area is located in a coastal plain area where the groundwater storage environment is relatively fragile and lacks water resources. Recognizing the regularity of groundwater circulation in this area and conducting an analysis of the evolution of groundwater quality can provide support for its potential as an emergency groundwater source. In order to assess the impact of emergency groundwater extraction on the surrounding environment, a 3-D groundwater flow and a solute displacement model were developed to quantify changes in water level, groundwater recovery capacity, salinity, and landing funnel. The numerical model was calibrated by values recorded with the actual observation well and solved by MODFLOW and MT3DMS modules in GMS (groundwater modeling system). The simulation results indicated that under the conditions of emergency grades I, II, and III, the maximum depths of the water level in the half year of mining were 38.5 m, 24 m, and 18.5 m, respectively, the areas of dropping funnel were 53.75 km(2), 33.026 km(2), and 25.273 km(2), respectively, and the widths of saltwater intrusion were 931 m, 585 m, and 413 m, respectively. The numerical simulation provides a reference for the rational allocation, development, and utilization of groundwater resources in the emergency water source area of the Hangzhou Bay New Area.

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The hydrological component of the Terrestrial Systems Modeling Platform (TerrSysMP), which includes integrated surface-groundwater flow, was used to investigate the grid resolution dependence of simulated soil moisture, soil temperature, and surface energy fluxes over a subcatchment of the Rur, Germany. The investigation was motivated by the recent developments of new earth system models, which include 3-D physically based groundwater models for the coupling of land-atmosphere interaction and subsurface hydrodynamics. Our findings suggest that for grid resolutions between 100 and 1000 m, the non-local controls of soil moisture are highly grid resolution dependent. Local vegetation, however, strongly modulates the scaling behavior, especially for surface fluxes and soil temperature, which depends on the radiative transfer property of the canopy. This study also shows that for grid resolutions above a few 100 m, the variation of spatial and temporal patterns of sensible and latent heat fluxes may significantly affect the resulting atmospheric mesoscale circulation and boundary layer evolution in coupled runs.

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In Pakistan, groundwater contributes about 40% in total water resources of the country and is considered a great source of fresh water which plays vibrant role in sustainability of irrigated agriculture. It is critical to safe and properly manage groundwater resources of the country for sustainable use. To ascertain groundwater potential areas and current status of the aquifer in the Upper Thal Doab, a part of Indus Basin in the Punjab Plain, an integrated approach of remote sensing (RS), Geographic Information System (GIS), and groundwater modeling has been adopted. Different input data sets like, geology, geomorphology, rainfall, land use/land cover, elevation, and drainage were overlaid and weighted to prepare groundwater potential zones map. The results classify the groundwater potential zones into three categories: good, moderate, and poor. The results demonstrate that about 12% of the study area is designated as good, 27% moderate, and 61% as poor. The groundwater modeling of the area was also carried out to find the current status of the aquifer, favorable sites for groundwater and predict future scenarios. The steady-state model was calibrated with the hydrological conditions of 1984 when the hydraulic heads were appeared to be in equilibrium condition. Transient simulations were calibrated for six stress periods with varying lengths commencing from 1985 to 2025. The mass balance analysis for transient model shows that the total outflows gradually increases than inflows from 1991 onwards due to increase in water extraction through water wells. The results demand to conduct periodic studies of the area to monitor the groundwater resources depletion if any in due course of time for timely management and precautionary measures.

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Numerical groundwater modelling to support mining decisions is often challenging and time consuming. Simulation of open pit mining for model calibration or prediction requires models that include unsaturated flow, large magnitude hydraulic gradients and often require transient simulations with time varying material properties and boundary conditions. This combination of factors typically results in models with long simulation times and/or some level of numerical instability. In modelling practice, long run times and instability can result in reduced effort for predictive uncertainty analysis, and ultimately decrease the value of the decision-support modelling. This study presents an early application of the Iterative Ensemble Smoother (IES) method of calibration-constrained uncertainty analysis to a mining groundwater flow model. The challenges of mining models and uncertainty quantification were addressed using the IES method and facilitated by highly parallelized cloud computing. The project was an open pit mine in South Australia that required predictions of pit water levels and inflow rates to guide the design of a proposed pumped hydro energy storage system. The IES calibration successfully produced 150 model parameter realizations that acceptably reproduced groundwater observations. The flexibility of the IES method allowed for the inclusion of 1493 adjustable parameters and geostatistical realizations of hydraulic conductivity fields to be included in the analysis. Through the geostatistical realizations and IES analysis, alternative conceptual models of fractured rock aquifer orientation and connections could be conditioned to observation data and used for predictive uncertainty analysis. Importantly, the IES method out-performed finite difference methods when model simulations contained small magnitude numerical instabilities.

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Many coastal aquifers are facing seawater intrusion due to overexploitation of freshwater. In this study, the groundwater flow and solute transport in a coastal aquifer of Minjur in India were simulated considering the possible cases of aquifer recharge, freshwater draft, relocation of pumping wells, etc., using numerical modelling software. The groundwater flow model MODFLOW and solute transport model MT3D were calibrated for seven years period and validated against the dataset for two years, which gave satisfactory results. The sensitivity analysis of model parameters revealed that the horizontal hydraulic conductivity greatly influenced the hydraulic head. The model was used to predict the response of the coastal aquifer to four potential scenarios like aquifer recharge, reduced pumping, relocation of pumping wells, and a combination of these scenarios. The effectiveness of various management scenarios was evaluated based on their ability to improve groundwater level and salinity in observation wells/piezometers, reduce the affected area and restrict the advancement of the seawater-freshwater interface. The result of predictive simulation indicated that a combination of scenarios such as reduction in groundwater pumping by 25% from the semi-confined aquifer, increased pumping by 25% from the unconfined aquifer, and increased recharge from rivers by constructing check dams have the potential to restrict the seawater-freshwater interface movement and improve groundwater quality in Minjur aquifer. These control measures would effectively shift the interface towards the coast by 1.0 km in the unconfined aquifer and 1.5 km in the semi-confined aquifer by 2025.

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Physically-based models of groundwater flow are powerful tools for water resources assessment under varying hydrologic, climate and human development conditions. One of the most important topics of investigation is how these conditions will affect the discharge of groundwater to rivers and streams (i.e. baseflow). Groundwater flow models are based upon discretized solution of mass balance equations, and contain important hydrogeological parameters that vary in space and cannot be measured. Common practice is to use least squares regression to estimate parameters and to infer prediction and associated uncertainty. Nevertheless, the unavoidable uncertainty associated with physically-based groundwater models often results in both aleatoric and epistemic model calibration errors, thus violating a key assumption for regression-based parameter estimation and uncertainty quantification. We present a complementary data-driven modeling and uncertainty quantification (DDM-UQ) framework to improve predictive accuracy of physically-based groundwater models and to provide more robust prediction intervals. First, we develop data-driven models (DDMs) based on statistical learning techniques to correct the bias of the calibrated groundwater model. Second, we characterize the aleatoric component of groundwater model residual using both parametric and non-parametric distribution estimation methods. We test the complementary data-driven framework on a real-world case study of the Republican River Basin, where a regional groundwater flow model was developed to assess the impact of groundwater pumping for irrigation. Compared to using only the flow model, DDM-UQ provides more accurate monthly baseflow predictions. In addition, DDM-UQ yields prediction intervals with coverage probability consistent with validation data. The DDM-UQ framework is computationally efficient and is expected to be applicable to many geoscience models for which model structural error is not negligible. (C) 2015 Elsevier Ltd. All rights reserved.

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In shallow alluvial aquifers characterized by coarse sediments, the evapotranspiration rates from groundwater are often not accounted for due to their low capillarity. Nevertheless, this assumption can lead to errors in the hydrogeological balance estimation. To quantify such impacts, a numerical flow model using MODFLOW was set up for the Tronto river alluvial aquifer (Italy). Different estimates of evapotranspiration rates were retrieved from the online Moderate Resolution Imaging Spectroradiometer (MODIS) database and used as input values. The numerical model was calibrated against piezometric heads collected in two snapshots (mid-January 2007 and mid-June 2007) in monitoring wells distributed along the whole alluvial aquifer. The model performance was excellent, with all the statistical parameters indicating very good agreement between calculated and observed heads. The model validation was performed using baseflow data of the Tronto river compared with the calculated aquifer-river exchanges in both of the simulated periods. Then, a series of numerical scenarios indicated that, although the model performance did not vary appreciably regardless of whether it included evapotranspiration from groundwater, the aquifer-river exchanges were influenced significantly. This study showed that evapotranspiration from shallow groundwater accounts for up to 21% of the hydrogeological balance at the aquifer scale and that baseflow observations are pivotal in quantifying the evapotranspiration impact.

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Surface refraction seismic surveys were conducted within a 7.3 km(2) east-central Pennsylvania watershed to characterize the geometry of its shallow layered and fractured bedrock, These data were augmented with observations from 29 rock cores, Hydraulic conductivity (K) of the bedrock was determined by interval packer testing within the boreholes. Finally, the MODFLOW ground water model was applied to the layered aquifer geometry in a three-dimensional format to determine watershed-scale aquifer parameters by model calibration to observed watershed data. Seismic testing showed that the aquifer could be characterized by four distinct layers, each with its own characteristic seismic velocity Hydraulic conductivity determined by field testing decreased with depth, ranging from greater than 1.0 m day(-1) in the shallow, highly fractured layer to approximately 0.01 m day(-1) in the regional aquifer, Its distribution with depth reflected the increase in seismic velocities and decrease in extent of fracturing observed in the cores. Aquifer geometry determined from seismic testing and rock cores was used to define model layer geometry, and K values from model calibration compared favorably to those determined by field testing. The ground water model was also used in calibration mode to determine specific yields (S-y) of the characteristic fracture layers, These were all low, ranging from 0.005 in the highly fractured layer to 0.0001 in the regional aquifer. When aquifer geometry determined from detailed seismic surveys is used as the basis for watershed-scale ground water modeling in these shallow layered and fractured systems, hydraulic parameters derived by field testing compare well to those determined by model calibration.

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The validation of variable-density flow models simulating seawater intrusion in coastal aquifers requires information about concentration distribution in groundwater. Electrical resistivity tomography (ERT) provides relevant data for this purpose. However, inverse modeling is not accurate because of the non-uniqueness of solutions. Such difficulties in evaluating seawater intrusion can be overcome by coupling geophysical data and groundwater modeling. First, the resistivity distribution obtained by inverse geo-electrical modeling is established. Second, a 3-D variable-density flow hydrogeological model is developed. Third, using Archie's Law, the electrical resistivity model deduced from salt concentration is compared to the formerly interpreted electrical model. Finally, aside from that usual comparison-validation, the theoretical geophysical response of concentrations simulated with the groundwater model can be compared to field-measured resistivity data. This constitutes a cross-validation of both the inverse geo-electrical model and the groundwater model.

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Bayesian inference using Markov Chain Monte Carlo (MCMC) provides an explicit framework for stochastic calibration of hydrogeologic models accounting for uncertainties; however, the MCMC sampling entails a large number of model calls, and could easily become computationally unwieldy if the high-fidelity hydrogeologic model simulation is time consuming. This study proposes a surrogate-based Bayesian framework to address this notorious issue, and illustrates the methodology by inverse modeling a regional MODFLOW model. The high-fidelity groundwater model is approximated by a fast statistical model using Bagging Multivariate Adaptive Regression Spline (BMARS) algorithm, and hence the MCMC sampling can be efficiently performed. In this study, the MODFLOW model is developed to simulate the groundwater flow in an arid region of Oman consisting of mountain-coast aquifers, and used to run representative simulations to generate training dataset for BMARS model construction. A BMARS-based Sobol' method is also employed to efficiently calculate input parameter sensitivities, which are used to evaluate and rank their importance for the groundwater flow model system. According to sensitivity analysis, insensitive parameters are screened out of Bayesian inversion of the MODFLOW model, further saving computing efforts. The posterior probability distribution of input parameters is efficiently inferred from the prescribed prior distribution using observed head data, demonstrating that the presented BMARS-based Bayesian framework is an efficient tool to reduce parameter uncertainties of a groundwater system. (C) 2018 Elsevier B.V. All rights reserved.

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This study presents an integrated modeling system for the evaluation of the quantity and quality of water resources of coastal agricultural watersheds. The modeling system consists of coupled and interrelated models, including (i) a surface hydrology model (UTHBAL), (ii) a groundwater hydrology model (MODFLOW), (iii) a crop growth/nitrate leaching model (REPIC, an R-ArcGIS-based EPIC model), (iv) a groundwater contaminant transport model (MT3DMS), and (v) a groundwater seawater intrusion model (SEAWAT). The efficacy of the modeling system to simulate the quantity and quality of water resources has been applied to the Almyros basin in Thessaly, Greece. It is a coastal agricultural basin with irrigated and intensified agriculture facing serious groundwater problems, such as groundwater depletion, nitrate pollution, and seawater intrusion. Irrigation demands were estimated for the main crops cultivated in the area, based on precipitation and temperature from regional weather stations. The models have been calibrated and validated against time-series of observed crop yields, groundwater table observations, and observed concentrations of nitrates and chlorides. The results indicate that the modeling system simulates the water resources quantity and quality with increased accuracy. The proposed modeling system could be used as a tool for the simulation of water resources management and climate change scenarios.

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Although integrated models are increasingly used for water management purposes, detailed applications of these models under different conditions are necessary to guide their implementation. The objective of this study was to examine some of the challenges encountered when simulating surface water-groundwater interactions in a post-glacial geological environment. The integrated Mike SHE model was used to simulate transient-state heads and flows in the Raquette River watershed in the Vaudreuil-Soulanges region of southwestern Quebec (Canada) over a 2-year period. This application benefited from a detailed hydrogeological database recently developed for the region. Overall, flows, heads and groundwater inputs to the river were adequately simulated. A sensitivity analysis has shown that many hydrogeologic and surface flow parameters have an impact on both flow rates and heads, thus underlining the importance of using an integrated model to study watershed-scale water issues. Additional flow rate measurements to improve the quality of rating curves and continuous flow measurements in tributaries could improve model calibration. An explicit simulation of unsaturated zone infiltration processes, including soil flow, plant and evaporation processes, as well as the inclusion of the agricultural tile drainage system, could reduce simulation errors. Extending the model calibration over a longer period, including contrasting hydrological conditions, would make the model more robust in view of its use for water management under land use and climate change conditions. Nevertheless, this work demonstrated that, using data readily available for southern Quebec aquifers, it is possible to build an integrated model that is representative of actual hydrological conditions. The maintenance and improvement of this model for long-term use is recommended.

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Groundwater modelling is an important management tool to study the behaviour of aquifer system under various hydrological stresses. Present study was carried out in deltaic regions of the Cauvery river, with an objective of estimating the minimum river flow required to improve the groundwater quality by numerical modelling. Cauvery river delta is the most productive agricultural plains of south India, but the agricultural activities during the last few decades have decreased due to limited flow in the river and increasing concentration of solutes in groundwater in the eastern parts. In order to understand the causes for increasing concentration, a three-layered finite-difference flow model was formulated to simulate the groundwater head and solute transport. The model was used to simulate the groundwater flow and solute transport for 5 years from July 2007 to June 2012. There was a fairly good agreement between the computed and observed groundwater heads. The chloride and nitrate ions were considered for solute transport modelling. Observed and simulated temporal variation in chloride and nitrate concentrations were comparable. The simulated solute concentrations from July 2007 to June 2012 showed an accumulation of solutes in groundwater of coastal part of the study area. The model was used to find the flow to be maintained in the river and rainfall recharge required to flush the ions into the sea. This can be achieved by maintaining minimal flow in the river and through regulation of fertilizer use as well as by creating awareness of sustainable use of groundwater in this area.

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Featured Application The topic developed in this paper can be useful for the optimization and the management of groundwater, particularly for aquifers drained by powerful springs tapped by aqueduct companies for water supply. Caposele spring catchment can be considered a sample aquifer from scientific point of view, given its hydraulic and hydrogeological features, widely studied and investigated over the time, representing an important source of water for many village of southern Italy. Different scenarios proposed for aquifer modelling offer to stakeholders a tool to pinpoint accurate strategies to safeguard water resources from contamination and climatic change which threaten it. Abstract The hydraulic and hydrogeological features of the Caposele aquifer have been investigated by using a numerical groundwater flow model. In particular, groundwater flow simulations were performed for a multilayered, unconfined aquifer in steady-state conditions for different thicknesses of the aquifer's saturated zone. The Caposele groundwater model was carried out starting from a generic model drained by a unique spring outlet in accordance with the geo-hydrological features of the study area. The conceptual model was built considering hydrogeological features of spring catchment, and was then implemented with the MODFLOW numerical code. A combined 2D-3D approach was adopted, and the model was calibrated on borehole data available for the time period 2012-2019. Different thicknesses of the aquifer were set, and a reliable relationship was found between the hydraulic head, saturated zone and hydraulic conductivity of the aquifer. Using the MODPATH package, the mean travel time (Darcian) of groundwater was computed for five different scenarios, corresponding to the model's depths; the analysis that was performed shows that the travel time is higher for a greater and lower for a smaller thickness of the aquifer's saturated zone, respectively. The Caposele aquifer model was zoned in different sectors, named flow pipe areas, that play different roles in groundwater recharge-discharge processes. A vector analysis was also carried out in order to highlight the ascendant flow near the spring zone.

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Nassau County, New York is presently developing a water management plan. In addressing the fundamental question of the ability of the aquifer to yield sufficient quantities of water for public supply, two approaches have been used. The first is hydrograph analysis of water levels over a 45-year period. The second approach involves using a three-dimensional, finite element ground-water model. Results include an analysis of the aquifer response to the stress of increased consumption and severe drought. Water balances are developed for each aquifer under predevelopment and present conditions. The technical analysis concludes that the aquifer can yield sufficient quantities of water, but present consumption also means diminished streamflow and potential salt-water intrusion. The paper also highlights how various planning perespectives effect the interpretation of the technical analysis. Purely technical information is not sufficient to reach a consensus on water issues. Education of the public and other participating agencies, as well as consensus-building techniques and public relations, are needed to develop an effective plan.

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Evaluating the sustainability of water uses in shallow aquifers is fundamental for both environmental and socio-economic reasons. Groundwater models are the main tools to sustain informed management plans, yet simulation results are affected by both epistemic and parametric uncertainties. In this study, we aim at investigating the effect of model uncertainties on three assessment criteria: depth to water (DTW), recharge/discharge analysis and a newly defined sustainability index S. We consider, as a case study, the shallow aquifer of the Adige Valley, which is highly influenced by surface water dynamics, water withdrawals from pumping wells and a dense network of ditches. Both direct measurements and soft data are used to reduce uncertainty associated to the limited knowledge about the spatial distribution of the hydraulic parameters. Simulation results showed that the aquifer is chiefly influenced by the interaction with the Adige River and that the influence of anthropogenic activities on vulnerability of groundwater resources varies within the study area. This calls for differentiated approaches to water resources management. Uncertainty related to the three assessment criteria is chiefly controlled by uncertainty of the hydrogeological model, although it depends also on the strategy adopted for the management of water resources.

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Effective management of water resource is essential in arid and semi-arid areas of India. In Bihar, for drinking purpose humans, livestock is dependent on the groundwater as well as in agricultural areas groundwater plays an important role in irrigation directly or indirectly. There is rise in the groundwater demand due to rapid population increase and fast industrialization. To meet this groundwater demand, excessive withdrawal of groundwater is a point of concern due to limited storage of it. Assessment of the groundwater was done by preparing a numerical model of the groundwater flow. This model is capable of solving large groundwater problems and associated complexity with it. In this study, a transient multi-layered groundwater flow model was conceptualized and developed for the Koshi River basin. In north Bihar plains, the Koshi River is one of the biggest tributaries of the Ganga River system. Koshi originates from the lower part of Tibet and joins the Ganga River in Katihar district, Bihar, India. After model development, calibration of the model was also done, by considering three model parameters, to represent the actual field conditions. For validation of the model, fifteen observation wells have been selected in the area. With the help of observation well data, computed and observed heads were compared. Comparison results have been found to be encouraging and the computed groundwater head matched with the observed water head to a realistic level of accuracy. Developed groundwater model is used to predict the groundwater head and flow budget in the concerned area. The study revealed that groundwater modeling is an important method for knowing the behavior of aquifer systems and to detect groundwater head under different varying hydrological stresses. This type of study will be beneficial for the hydrologist and water resource engineers to predict the groundwater flow behavior, before implementing any project or to implement a correction scheme.

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Using a three-dimensional finite element model, this study characterizes groundwater flow in a costal plain of the Seto Inland Sea, Japan. The model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow. Geological geometry and the number of aquifers have been analyzed based on a large amount of geological, hydrogeological and topographical data. Results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer. For calibrating the numerical groundwater model, the groundwater flow was simulated in steady state. In addition, the groundwater level and trend in the transient state has also been elucidated. The numerical result provides excellent visual representations of groundwater flow, presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways. Results build a base for further analysis under different future scenarios.

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The objective of this article is to develop and implement a comprehensive computer model that is capable of simulating the surface-water, ground-water, and stream-aquifer interactions on a continuous basis for the Rattlesnake Creek basin in southcentral Kansas, The model is to be used as a tool for evaluating long-term water-management strategies. The agriculturally-based watershed model SWAT and the ground-water model MODFLOW with stream-aquifer interaction routines, suitably modified, were linked into a comprehensive basin model known as SWATMOD. The hydrologic response unit concept was implemented to overcome the quasi-lumped nature of SWAT and represent the heterogeneity within each subbasin of the basin model. A graphical user-interface and a decision support system were also developed to evaluate scenarios involving manipulation of water rights and agricultural land uses on stream-aquifer system response. An extensive sensitivity analysis on model parameters was conducted, and model limitations and parameter uncertainties were emphasized. A combination of trial-and-error and inverse modeling techniques were employed to calibrate the model against multiple calibration targets of measured ground-water levels, streamflows, and reported irrigation amounts, The split-sample technique was employed for corroborating the calibrated model. The model was run for a 40 y historical simulation period, and a 40 y prediction period. A number of hypothetical management scenarios involving reductions and variations in withdrawal rates and patterns were simulated. The SWATMOD model was developed as a hydrologically rational low-flow model for analyzing, in a user-friendly manner, the conditions in the basin when then is a shortage of water. (C) 1999 Elsevier Science B.V. All rights reserved.

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The advancement of seawater intrusion in coastal aquifers using three-dimensional variable density transport models is examined. The fluid flow and mass transport processes are considered and the resulting differential equations are solved numerically using finite element method. A constraint based boundary condition regarding chloride concentration is imposed oil the seaside boundary. The numerical models are applied to an unconfined aquifer located in the central part of Thira Island (Santorini). Several scenarios are examined corresponding to steady-state and time-dependent conditions. Two potential cases of aquifer replenishment, with natural and artificial recharge are also simulated. The results demonstrate significant dependence of the advancement of seawater intrusion oil the initial and boundary conditions prevailing on the seaside boundary of the aquifer. The transition zone predicted by variable density flow and transport models is of considerable width indicating the necessity for modelling using advanced three-dimensional variable density transport models.

ABSTRACT:

Three-dimensional ground-water modeling experiments were done to test the hypothesis that regional ground-water flow is an important component of the water budget in the Glacial Lake Agassiz Peatlands of northern Minnesota. Previous data collected from the Glacial Lake Agassiz Peatlands suggest that regional ground-water flow discharges to these peatlands, maintaining saturation, controlling the peat pore-water chemistry, and driving ecological change. To test this hypothesis, steady-state MODFLOW models were constructed that encompassed an area of 10,160 km(2). Data used in this modeling project included surface-water and water-table elevations measured across the study area, digital elevation data, and well logs from scientific test wells and domestic water wells drilled in the study area. Numerical simulations indicate that the Itasca Moraine, located to the south of the peatland, acts as a recharge area for regional ground-water flow. Ground water recharged at the Itasca Moraine did not discharge to the Red Lake Peatlands, but rather was intercepted by the Red Lakes or adjacent rivers. Simulations suggest that ground-water flow within the peatlands consists of local-flow systems with streamlines that are less than 10 km long and that ground water from distant recharge areas does not play a prominent role in the hydrology of these peatlands. Ground-water flow reversals previously observed in the Red Lake Peatlands are either the result of interactions between local and intermediate-scale flow systems or the transient release of water stored in glacial sediments when the watertable is lowered. (C) 2001 Elsevier Science B.V. All rights reserved.

ABSTRACT:

In the context of climate change, it is important to understand possible future projections and historical trends of groundwater recharge, flow, and discharge to surface reservoirs. Knowledge of a vast range of possible conditions is required to fully appreciate the variability of the hydrologic cycle and hence the long-term vulnerability of groundwater-dependent habitats. This research investigates historical trends for a groundwater-surface water interacting system that supports a fragile ecosystem in southern Quebec. A transient model was developed using MODFLOW to simulate site-wide groundwater flow for the study area. The model was used to simulate past hydrogeological conditions (1900-2010) using a new data set of available precipitation (rain and snowmelt) and temperature. This data set was used to simulate the overall groundwater budget and to determine groundwater discharge (river baseflow and spring flow) in the study area. This allows for the quantification of century-long trends in flow data, as well as the extreme maximum and minimum flows over 110 years. Recharge was variable, ranging from 41 to 197 mm/year over the study period. Lower recharge rates from 1950 to 1965 induced marked effects on spring flow. Although the trend is not statistically significant, there appears to be, for the second half of the study period (1966-2010), a tendency towards a reversal to an increase for recharge, hydraulic heads, spring flow and baseflows. A longer time series would be necessary to confirm this tendency. The simulated historical trends are compared with flow projections for future scenarios (2041-2070). The confirmation that the natural system has been subjected to a wide range of climatic conditions over the last century helps to inform about its resilience. This study highlights the utility of groundwater flow modeling using historical climate data sets to gain a better understanding of long-term trends for climate change-related hydrogeological and ecohydrological studies.

ABSTRACT:

The study area Hindon -Yamuna interfluve region is underlain by a thick pile of unconsolidated Quaternary alluvial deposits and host multiple aquifer system. Excessive pumping in the last few decades, mainly for irrigation, has resulted in a significant depletion of the aquifer. Therefore, proper groundwater management of Hindon-Yamuna interfluve region is necessary. For effective groundwater management of a basin it is essential that careful zone budget study should be carried out. Keeping this in view, groundwater flow modelling was attempted to simulate the behavior of flow system and evaluate zone budget. Visual MODFLOW, pro 4.1 is used in this study to simulate groundwater flow. The model simulates groundwater flow over an area of about 1345 km(2) with a uniform grid size of 1000 m by 1000 m and contains three layers, 58 rows and 37 columns. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW, pro 4.1. The river - aquifer interaction was simulated using the river boundary package. Simulated pumping rates of 500 m(3)/day, 1000 m(3)/day and 1500 m(3)/day were used in the pumping well package.The zone budget for the steady state condition of study area indicated that the total annual direct recharge is 416.10 MCM and the total annual groundwater draft through pumping is of the order of 416.63 MCM. Two scenarios were considered to predict aquifer system response under different conditions. Sensitivity analysis on model parameters was conducted to quantitatively evaluate the impact of varying model inputs. Based on the results obtained from the sensitivity analysis, it was found that the model is more sensitive to hydraulic conductivity and recharge parameter. Present study deals with importance of groundwater modelling for planning, design, implementation and management of groundwater resources.

ABSTRACT:

Pumping-induced leakage across aquitards may induce a deterioration of water quality in multi-layer aquifer systems. It is critical to understand long-term trends of water quality parameters when assessing the sustainability of groundwater abstraction. Daily drinking water needs of 2.2 million people in Yinchuan region of northwest China are solely met by groundwater resources, but long-term groundwater withdrawal has created an extensive cone of depression (294 km(2) in area) in confined aquifer causing increased vertical recharge. In this study, a model was established and calibrated with head data, then was incorporated with field tracer tests to provide key information on the hydro-dispersive characteristics of the contaminant for assessing both the current and future state of the aquifer system. The results confirmed a close association between water quality deterioration and high downward fluxes of high chloride groundwater, most notably near the center of the cone of depression. On a temporal scale, water quality degradation remains slow, largely due to the high, pre-existing storage of good quality water. Modeling suggests that the water quality in the upper confined aquifer will lose its potability over a 25 km(2) and 50 km(2) area within 200 years under the current and intensified pumping conditions, respectively. Elevated chloride values were also detected toward the east of the cone, highlighting the impact of hydrological settings on the vertical groundwater flow. Modeling of potential aquifer remediation shows an even slower response with a further 250 years or more required for potability to be restored in affected areas. The findings can provide valuable guidance to for decision makers and support the sustainable management of aquifer exploitation. (c) 2020 Elsevier Ltd. All rights reserved.

ABSTRACT:

Recognitions and predictions of the contamination origin are essential steps in the protective measures to avoid well-water contamination and the first step in managing groundwater resources. In this regard, finite-difference model software (GMS 10.0.6) was used to model the transport path, the origin of contaminants and to determine the wellhead protection area in Iranshahr aquifer. Since contamination transport models require a calibrated groundwater flow model, we first prepared this model. Accordingly, after collecting all geological, meteorological, hydrological and hydrogeological data (based on the maps, geophysical tests and exploratory borehole drilling, rainfall statistics and groundwater level in exploitation wells), a database was constructed in ArcGis10.1 software and a conceptual model was developed by transporting this information to GMS software. Based on the developed model, the aquifer's groundwater level was simulated, calibrated and validated using MODFLOW2000 code in GMS software. The particle transport model in the aquifer was provided to examine and model the transport path and the origin of contaminants through MODPATH module. In the end, the aquifer wells' protection area against contaminants was illustrated. According to the results, contaminant transport path in the wells of central plains is directed from the river to the wells, in forward particle-tracking model; the maximum time taken by particles is 508,952.5 days, the minimum time is 144 days, and the average radius of 50-day wellhead protection area based on the protection against contaminations such as pathogenic bacteria in Iranshahr aquifer was determined to be about 100 m.

ABSTRACT:

Due to inherent uncertainties associated with the groundwater system characterization, the model calibration is the significant step for the obtaining of the reliable predictions that could be used in long-term safety assessment. The following paper is focused on the modelling of the groundwater flow in heterogeneous media using the data of the geological engineering survey for the prospective site of the radioactive waste deep geological disposal at Nizhnekansky granite-gneiss crystalline rock massif (Krasnoyarsk Territory). This case study illustrates the efficiency of heuristic optimization methods and hybridization approach for the calibration of groundwater models.

Note: Bounding box location set generally around Krasnoyarsk since exact location unknown.

ABSTRACT:

In the framework of evaluating the safety of a radioactive waste disposal in deep argillaceous formations and its assessment by the implementer, IRSN and MINES ParisTech built a hydrogeological model of the Paris Basin aquifer system with the aim of identifying radionuclide pathways, estimating transfer times associated with those pathways and locating potential outlets. Such modelling of fluid and mass transport through a sedimentary basin is a recurrent applied geology study. However, recent research shows that in a deep and saline environment, density effects induced by both temperature (to a small extent) and particularly salt concentration can play a major role in the predicted groundwater flow pathways. The present study highlights the relevance of building a hydrogeological model from the measured hydrogeological and hydrogeochemical parameters by combining the calibration of the piezometric levels and the salinity values simultaneously. The application of this strategy to the Paris Basin shows that the Keuper halite formation (Triassic), located in the eastern part of the basin, can be considered as the unique salt source, provided that the density effects are taken into account in the flow and transport modelling. The calibration requires, in particular, to also take into account some of the basin's major tectonic faults, which allow vertical hydraulic connections between aquifers and thus allow salt water fluxes toward the shallower formations. The results presented in this paper show that when considering "thermohaline" effects, the model effectively reproduces the observed hydraulic heads and salinity values throughout the entire Paris Basin, whilst at the same time outlining the role of faults and of the geometry of geological formations on salt transport. (C) 2012 Elsevier B.V. All rights reserved.

ABSTRACT:

The assembly of a groundwater flow model for the shallow aquifer in Tianjin Municipality is outlined in this paper. Tianjin Municipality was selected because of its complicated hydrogeological conditions and rich data, which could be used to test a refined groundwater flow model for the shallow aquifer. When a shallow groundwater flow model is being assembled its recharge and discharge functions need to represent inflows from rainfall, irrigation return flows, seepage from rivers and reservoirs, and lateral inflows and outflows from evaporation, abstraction of groundwater for irrigation and industrial, and urban use. When abstracting groundwater, the water exchanges between a shallow aquifer and a deep aquifer also need to be considered. The real irrigation areas of Tianjin Municipality were input into the groundwater flow model, and the rivers and reservoirs were refined to the level of secondary tributaries and small scale reservoirs. The model calibration was carried out based on consideration of representative parameter values and their spatial distribution, the groundwater flow fields, the temporal variation in groundwater heads and the water balance for the years 2006-2008. It was concluded from a comparison of the observed and simulated groundwater heads that the precision of the model is high and that the simulated groundwater levels align with the real groundwater conditions. It is also concluded that the groundwater flow model for the shallow aquifer in Tianjin Municipality will be a useful tool for further studies about the relationship between shallow and deep aquifers and the surface environment.

ABSTRACT:

A numerical assessment of seawater intrusion in Gaza, Palestine, has been achieved applying a 3-D variable density groundwater flow model. A two-stage finite difference simulation algorithm was used in steady state and transient models. SEAWAT computer code was used for simulating the spatial and temporal evolution of hydraulic heads and solute concentrations of groundwater. A regular finite difference grid with a 400 m(2) cell in the horizontal plane, in addition to a 12-layer model were chosen. The model has been calibrated under steady state and transient conditions. Simulation results indicate that the proposed schemes successfully simulate the intrusion mechanism. Two pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and solute concentrations in the groundwater for a planning period of 17 years. The results show that seawater intrusion would worsen in the aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area, to moderate pumpage rates from water supply wells far from the seashore and to increase the aquifer replenishment by encouraging the implementation of suitable solutions like artificial recharge, may limit significantly seawater intrusion and reduce the current rate of decline of the water levels.

ABSTRACT:

A groundwater system model was developed and calibrated in the study area of Lehman Creek Watershed, eastern Nevada. The model development aims for integrating the surface hydrologic model-precipitation runoff modeling system (PRMS) model-with the three-dimensional (3D) finite-difference model MODFLOW. A two-layer groundwater model was developed with spatial discretization of 100 x 100 m grid. The water balance was estimated with inflows of gravity drainage and initial streamflow estimated from a calibrated PRMS model, and with outflows of spring discharges, boundary fluxes, and stream base flow. A steady-state model calibration was performed to estimate the hydraulic properties. The modeling results were able to represent the geographic relieves, simulate water balance components, and capture the hydrogeologic features. The preliminary results presented in this study provide insights into the local groundwater flow system and lay groundwork for future study of interactive influences of surface hydrologic variation.

ABSTRACT:

This study aims to determine the safe and sustainable development and management of groundwater resources in Ergene River Basin located in northwestern Turkey. A numerical groundwater model was developed for the Sandy Complex aquifer, which is the most productive and the most widespread aquifer in the basin. The finite difference model with 5900 cells was used to represent the steady and unsteady flow in the aquifer. The model was calibrated in two steps: a steady state calibration by using the observed groundwater levels of January 1970, followed by a transient calibration by using the observed groundwater levels for the period of January 1970 and December 2000. The resulting model was used to develop groundwater pumping scenarios in order to predict the changes in the aquifer system under a set of different pumpage conditions for a planning period of 30 years between January 2001 and December 2030. A total of eight pumping scenarios were developed under transient flow conditions for the planning period and the results were evaluated to determine the safe and sustainable yields of the aquifer. The results, presented in the form of a trade-off curve, demonstrate that the continuation of the present pumping rates exceeds both the safe and the sustainable yields of the aquifer system.

ABSTRACT:

Ground penetrating radar (GPR) has proved to be an extremely useful geophysical tool, in conjunction with direct geological data, to develop a realistic, macroscopic, subjective-based conceptual model of aquifer architecture within a shallow coastal alluvial plain. Subsequent finite-difference groundwater modelling has not only enabled determination of the dominant groundwater flow paths for the plain, but has also quantified the effects of within-facies and between-facies sedimentary heterogeneity on those flow paths. The interconnection of narrow, unconfined alluvial channels and a broad, semi-confined alluvial delta is ensuring that most fresh groundwater that enters the plain in the form of precipitation or recharge from lateral bedrock hills, is discharged into the eastern coastal wetlands via that alluvial delta aquifer.

ABSTRACT:

Increased irrigation in Kansas and other regions during the last several decades has caused serious water depletion, making the development of comprehensive strategies and tools to resolve such problems increasingly important. This paper makes the case for an intermediate complexity quasi-distributed, comprehensive, large-watershed model, which falls between the fully distributed, physically based hydrological modeling system of the type of the SHE model and the lumped, conceptual rainfall-runoff modeling system of the type of the Stanford watershed model. This is achieved by integrating the quasi-distributed watershed model SWAT with the fully-distributed ground-water model MODFLOW. The advantage of this approach is the appreciably smaller input data requirements and the use of readily available data (compared to the fully distributed, physically based models), the statistical handling of watershed heterogeneities by employing the hydrologic-response-unit concept, and the significantly increased flexibility in handling stream-aquifer interactions, distributed well withdrawals, and multiple land uses. The mechanics of integrating the component watershed and ground-water models are outlined, and three real-world management applications of the integrated model from Kansas are briefly presented. Three different aspects of the integrated model are emphasized: (1) management applications of a Decision Support System for the integrated model (Rattlesnake Creek subbasin); (2) alternative conceptual models of spatial heterogeneity related to the presence or absence of an underlying aquifer with shallow or deep water table (Lower Republican River basin); and (3) the general nature of the integrated model linkage by employing a watershed simulator other than SWAT (Wet Walnut Creek basin). These applications demonstrate the practicality and versatility of this relatively simple and conceptually clear approach, making public acceptance of the integrated watershed modeling system much easier. This approach also enhances model calibration and thus the reliability of model results. (C) 2000 Elsevier Science B.V. All rights reserved.

ABSTRACT:

Groundwater flow in the Leon-Chinandega aquifer was simulated using transient and steady-state numerical models. This unconfined aquifer is located in an agricultural plain in northwest Nicaragua. Previous studies were restricted to determining groundwater availability for irrigation, overlooking the impacts of groundwater development. A sub-basin was selected to study the groundwater flow system and the effects of groundwater development using a numerical groundwater flow model (Visual MODFLOW). Hydrological parameters obtained from pumping tests were related to each hydrostratigraphic unit to assign the distribution of parameter values within each model layer. River discharge measurements were crucial for constraining recharge estimates and reducing the non-uniqueness of the model calibration. Steady-state models have limited usefulness because of the major variation of recharge and agricultural pumping during the wet and dry seasons. Model results indicate that pumping induces a decrease in base flow, depleting river discharge. This becomes critical during dry periods, when irrigation is highest. Transient modeling indicates that the response time of the aquifer is about one hydrologic year, which allows the development of management strategies within short time horizons. Considering further development of irrigated agriculture in the area, the numerical model can be a powerful tool for water resources management.

ABSTRACT:

A fully integrated, physically-based MIKE SHE/MIKE11 model was developed for the Mokolo River basin flow system to simulate key hydraulic and hydrologic indicator inputs to the Downstream Response to Imposed Flow Transformation for Arid Rivers (DRIFT-ARID) decision support system (DSS). The DRIFT-ARID tool is used in this study to define environmental water requirements (EWR) for non-perennial river flow systems in South Africa to facilitate ecosystem-based management of water resources as required by the National Water Act (Act No. 36 of 1998). Fifty years of distributed daily climate data (1950 to 2000) were used to calibrate the model against decades of daily discharge data at various gauges, measurements of Mokolo Dam stage levels, and one-time groundwater level measurements at hundreds of wells throughout the basin. Though the calibrated model captures much of the seasonal and post-event stream discharge response characteristics, lack of sub-daily climate and stream discharge data limits the ability to calibrate the model to event-level system response (i.e. peak flows). In addition, lack of basic subsurface hydrogeologic characterisation and transient groundwater level data limits the ability to calibrate the groundwater flow model, and therefore baseflow response, to a high level. Despite these limitations, the calibrated model was used to simulate changes in hydrologic and hydraulic indicators at five study sites within the basin for five 50-year land-use change scenarios, including a present-day (with dam), natural conditions (no development/irrigation), and conversion of present-day irrigation to game farm, mine/city expansion, and a combination of the last two. Challenges and recommendations for simulating the range of non-perennial systems are presented.

ABSTRACT:

The Republic of Djibouti has an area of 23,000 km(2), a coastline 370 km long and a population of 820,000 inhabitants. It experiences an arid climate characterized by high daytime temperatures and low and irregular rainfall (average of 140 mm/year), resulting in continuous periods of drought. These difficult climatic conditions and the absence of perennial surface water have progressively led to an intensive exploitation of groundwater to meet increasing water demands in all sectors (drinking water, agriculture and industries). In coastal areas, seawater intrusion constitutes a significant additional risk of groundwater degradation. This study is focused on the coastal aquifer of Tadjourah which supplies water to the city of Tadjourah, currently comprising 21,000 inhabitants. The main objective of this work is to assess the current resources of this aquifer; its capacity to satisfy, or not, the projected water demands during coming years; and to analyze its vulnerability to seawater intrusion within the frame of climate change. Three RCPs (Representative Concentration Pathway) were used to simulate different climate scenarios up to 2100. The simulated rainfall series allowed to deduce the aquifer recharge up to 2100. The code Seawat was used to model seawater intrusion into the aquifer, using the recharge data deduced from the climate scenarios. The results indicate that the risk of contamination of the Tadjourah coastal aquifer by seawater intrusion is high. The long-term and sustainable exploitation of this aquifer must take into consideration the impact of climate change.

ABSTRACT:

The use of groundwater flow models is prevalent in the field of environmental hydrogeology. Models have been applied to investigate a wide variety of hydrogeological conditions. Recently, groundwater models have been applied to predict the fate and transport of contaminants for risk evaluation purposes. In this paper, a transient groundwater flow model in Daxing district of Beijing, China was developed. The conceptual model was built by analyzing the hydrogeological data. Hydraulic conductivities have been calibrated by the steady state model. The storage coefficients are calibrated by the transient model based on the available data observed from 1995 to 2000, which provides insights to understand the dynamic behavior of groundwater systems and to predict spatial-temporal distributions of groundwater levels in responding to changes. The model results help to identify the aquifer properties and to analyze the groundwater flow dynamics, the changes of groundwater levels, in addition, the improvement of the groundwater level monitoring network will be proposed through the analysis of groundwater levels. The calibrated transient model will be used later to predict the impacts of water resources management schemes on groundwater in the study area. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the organizing committee of 2nd International Conference on Advances in Energy Engineering (ICAEE).

ABSTRACT:

For the implementation of the European Union Water Framework Directive (WFD), technological and scientific support are required. This paper presents a methodology to support a first step of the implementation of WFD, which is the delineation of groundwater bodies. The methodology consists of (1) the development of a complete and generally-accepted hydrogeological classification system for Flanders, named the HCOV code, (2) the development of a geographic information systems (GIS)-managed borehole database, and (3) the development of aquifer and aquitard models by means of a solid modeling approach. For each unit of the hydrogeological classification code for Flanders unit, GIS maps are generated for the three basic characteristics of hydrogeological layers: extent, base level and thickness, such that combined, the volume and extent of a hydrogeological layer is unambiguously defined. This GIS-based hydrogeological database has become a useful tool for groundwater management purposes and to provide the input for groundwater modeling.

ABSTRACT:

Reliable ground water models require both an accurate physical representation of the system and appropriate boundary conditions. While physical attributes are generally considered static, boundary conditions, such as ground water recharge rates, can be highly variable in both space and time. A practical methodology incorporating the hydrologic model HELP3 in conjunction with a geographic information system was developed to generate a physically based and highly detailed recharge boundary condition for ground water modeling. The approach uses daily precipitation and temperature records in addition to land use/land cover and soils data. The importance of the method in transient ground water modeling is demonstrated by applying it to a MODFLOW modeling study in New Jersey. In addition to improved model calibration, the results from the study clearly indicate the importance of using a physically based and highly detailed recharge boundary condition in ground water quality modeling, where the detailed knowledge of the evolution of the ground water flowpaths is imperative. The simulated water table is within 0.5 m of the observed values using the method, while the water levels can differ by as much as 2 m using uniform recharge conditions. The results also show that the combination of temperature and precipitation plays an important role in the amount and timing of recharge in cooler climates. A sensitivity analysis further reveals that increasing the leaf area index, the evaporative zone depth, or the curve number in the model will result in decreased recharge rates over time, with the curve number having the greatest impact.

ABSTRACT:

A ground-water model was developed for Miami-Dade County Florida, which lies within the Southeast Atlantic Coastal Zone, as a predictive tool that will be used to analyze different water-management scenarios, including regional water-supply plans and the Comprehensive Everglades Restoration Plan (CERP). The model is being developed by the South Florida Water Management District (SFWMD) based on a modified version of the US Geological Survey modular three-dimensional, finite-difference, ground-water-flow model (MODFLOW). This version includes the wet-land and Diversion packages, which are MODFLOW modules that enable the top layer of the grid system to include overland flow through dense vegetation, channel flow through a slough network, and interaction With levees, and thus can closely simulate the natural system. The model domain is discretized into 430 rows by 367 columns with a uniform cell size of 500 ft x 500 ft (152.4 m). Four horizontal layers are used to represent lithologic zones within the surficial aquifer, one of the most transmissive aquifers in the world, with transmissivity values as high as 300,000 ft(2)/d (27,870.9 m(2)/d). Boundary conditions were established by water levels in canals on the northern and southern edges of the modeled region and by water-level measurements in wet-lands along the western edge. The eastern boundary with the Atlantic Ocean was determined by using mean tidal fluctuations to calculate the equivalent fresh-water head. The main advantage of this model, besides the high degree of detail and the number of variables, is that it can simulate hydroperiods within wetland areas using the Wet-land and Diversion packages. These packages allow the model to represent the full hydrologic cycle within the wetland areas, including sources and sinks on a daily basis, starting with total precipitation as a driving force. During calibration (1988-90), a very low sensitivity to conductivity and canal conductances was observed. Therefore, the fit between the model-computed water levels and the observed historical ground-water levels was achieved mainly by adjusting general head boundary conditions and wetland parameters within the active domain. The model is highly sensitive to the operational rules, especially the stages at which the canals are maintained, and is therefore responsive to the way that the system is managed.

ABSTRACT:

Groundwater is a valuable resource of limited extent both in quantity and in space. In order to ensure its careful use, proper evaluation of its availability is required. The majority of groundwater flow numerical models still provide only deterministic predictions with no supplementary information on uncertainty predictions. Stochastic groundwater management aims at treating uncertainty within decision oriented models in a logical and systematic manner which cannot be experienced in deterministic modelling approach. This paper presents a detailed methodology followed in the development of a stochastic groundwater model under uncertain recharge. The methodology is comprised of two steps (1) The development of a groundwater flow model and (2) the development of a stochastic solutionstochastic groundwater flow model considering recharge as uncertain parameter. The groundwater flow model was developed and simulated using MODFLOW 20 0 0 software and calibrated using Parameter Estimation Program (PEST). Validated model compared well with calibrated model. The uncertainty in recharge was propagated to the flow model through Monte Carlo (MC) sampling technique. The methodology demonstrated the importance of developing groundwater flow models that acknowledge the existence of recharge uncertainty and hence consider it in the development of groundwater management solutions. (C) 2020 The Author(s). Published by Elsevier B.V.

ABSTRACT:

Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for efficient hydraulic conductivity (K) characterization along vertical profiles with sampling resolutions of up to a few centimetres. Until date, however, only a limited number of studies document high-resolution in situ DP data for three-dimensional conceptual hydrogeological model development and groundwater flow model parameterization. This study demonstrates how DP technologies improve building of a conceptual hydrogeological model. We further evaluate the degree to which the DP-derived hydrogeological parameter K, measured across different spatial scales, improves performance of a regional groundwater flow model. The study area covers an area of similar to 60 km(2) with two overlying, mainly unconsolidated sand aquifers separated by a 5-7 m thick highly heterogeneous clay layer (in northeastern Belgium). The hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests (CPTs). The hydrogeological parameter K was derived from a combined analysis of core and CPT data and also from hydraulic direct push tests. A total of 50 three-dimensional realizations of K were generated using a non-stationary multivariate geostatistical approach. To preserve the measured K values in the stochastic realizations, the groundwater model K realizations were conditioned on the borehole and direct push data. Optimization was performed to select the best performing model parameterization out of the 50 realizations. This model outperformed a previously developed reference model with homogeneous K fields for all hydrogeological layers. Comparison of particle tracking simulations, based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields, demonstrate the impact DP-derived subsurface heterogeneity in K can have on groundwater flow and solute transport. We demonstrated that DP technologies, especially when calibrated with site-specific data, provide high-resolution 3D subsurface data for building more reliable conceptual models and increasing groundwater flow model performance. (C) Springer-Verlag Berlin Heidelberg 2014

ABSTRACT:

The Zhangye basin is in the middle reaches of the Heihe River, northwestern China. Heavy abstraction of groundwater since the 1970s in the area is for agricultural, industrial and drinking water supplies and has led to a substantial decline in the potentiometric surface. A three-dimensional regional numerical groundwater flow model, calibrated under transient conditions, has been developed and used to predict the drawdown for the period from 2000 to 2030 under two different groundwater management scenarios.

ABSTRACT:

With respect to model parameterization and sensitivity analysis, this work uses a practical example to suggest that methods that start with simple models and use computationally frugal model analysis methods remain valuable in any toolbox of model development methods. In this work, ground-water model calibration starts with a simple parameterization that evolves into a moderately complex model. The model is developed for a water management study of the TivoliGuidonia basin (Rome, Italy) where surface mining has been conducted in conjunction with substantial dewatering. The approach to model development used in this work employs repeated analysis using sensitivity and inverse methods, including use of a new observation-stacked parameter importance graph. The methods are highly parallelizable and require few model runs, which make the repeated analyses and attendant insights possible. The success of a model development design can be measured by insights attained and demonstrated model accuracy relevant to predictions. Example insights were obtained: (1) A long-held belief that, except for a few distinct fractures, the travertine is homogeneous was found to be inadequate, and (2) The dewatering pumping rate is more critical to model accuracy than expected. The latter insight motivated additional data collection and improved pumpage estimates. Validation tests using three other recharge and pumpage conditions suggest good accuracy for the predictions considered. The model was used to evaluate management scenarios and showed that similar dewatering results could be achieved using 20 % less pumped water, but would require installing newly positioned wells and cooperation between mine owners.

ABSTRACT:

Alluvial aquifers by nature are complex caused by varied depositional environments. Developing a reliable groundwater model to represent an alluvial aquifer is non-trivial. Also, relying on a single best calibrated model may not be sufficient because of an inadequate choice of model parameter values. To better understand groundwater dynamics and improve model prediction reliability, this study presents a Bayesian multi-model uncertainty quantification (BMMUQ) framework to account for model parameter uncertainty in complex alluvial groundwater modeling. The methodology was applied to the agriculturally intensive Mississippi River alluvial aquifer (MRAA), Northeast Louisiana. An aquifer architecture was first constructed using 7,259 well logs in the MRAA area which covers three fluvial deposits (alluvium, braided-stream terrace, and braided-stream terrace-loess). A 12-layer MODFLOW model was then developed to address the alluvial aquifer complexity and well calibrated through a genetic algorithm. This study quantified model parameter uncertainty in hydraulic conductivity and specific storage of sand facies. Bayesian model averaging (BMA) with the Expectation Maximization (EM) algorithm was adopted to derive posterior model weights and head variances of 50 alternative conceptual groundwater flow models, and thereby obtains BMA ensemble model predictions instead of only relying on the best calibrated conceptual model. Results show that an estimated around 950 million m(3) of groundwater storage loss occurs in 2015 with respect to the beginning of 2004, due to high groundwater demand for irrigation in the MRAA area. Explicitly quantifying model uncertainty can produce more reliable groundwater level predictions from BMA ensemble model. The presented groundwater modeling framework improves our understanding of the MRAA and provides a valuable tool to assist agricultural water management.

ABSTRACT:

This paper presents a study of solute transport through ground water in the saturated zone and the resulting breakthrough curves (BTCs), using a field-scale numerical model that incorporates the processes of advection, dispersion, matrix diffusion in fractured volcanic formations, sorption, and colloid-facilitated transport. Such BTCs at compliance boundaries are often used as performance measures for a site. The example considered here is that of the saturated zone study prepared for the Yucca Mountain license application. The saturated zone at this site occurs partly in volcanic, fractured rock formations and partly in alluvial formations. This paper presents a description of the site and the ground water flow model, the development of the conceptual model of transport, model uncertainties, model validation, and the influence of uncertainty in input parameters on the downstream BTCs at the Yucca Mountain site. (c) 2010 Elsevier By. All rights reserved.

ABSTRACT:

Water and energy cycles interact, making these two processes closely related. Land surface models (LSMs) can describe the water and energy cycles on the land surface, but their description of the subsurface water processes is oversimplified, and lateral groundwater flow is ignored. Groundwater models (GWMs) describe the dynamic movement of the subsurface water well, but they cannot depict the physical mechanisms of the evapotranspiration (ET) process in detail. In this study, a coupled model of groundwater flow with a simple biosphere (GWSiB) is developed based on the full coupling of a typical land surface model (SiB2) and a 3-D variably saturated groundwater model (AquiferFlow). In this coupled model, the infiltration, ET and energy transfer are simulated by SiB2 using the soil moisture results from the groundwater flow model. The infiltration and ET results are applied iteratively to drive the groundwater flow model. After the coupled model is built, a sensitivity test is first performed, and the effect of the groundwater depth and the hydraulic conductivity parameters on the ET are analyzed. The coupled model is then validated using measurements from two stations located in shallow and deep groundwater depth zones. Finally, the coupled model is applied to data from the middle reach of the Heihe River basin in the northwest of China to test the regional simulation capabilities of the model.

ABSTRACT:

With the significant advancements in Information and Communications Technology (ICT), cloud based applications provide a novel approach to access applications which are not installed on the local computers. The integration of cloud computing and Internet of Things (IoT) indicated a bright future of the Internet. In this paper, a new architecture of cloud computing Model as a Service (MaaS) is proposed. The feasibility of the proposed architecture is proved by implementing a groundwater model on cloud as a case study. The groundwater model is established using MODFLOW for the middle reach of the Heihe River Basin (HRB). The model is calibrated using in situ observation to ensure capability of simulating the groundwater process with Root Mean Square Error (RMSE) of 1.70 m and coefficient of determination (R-2) of 0.64. The parameter uncertainties of the groundwater model are analyzed by sequential data assimilation algorithms (PF, Particle Filter; EnKF, Ensemble Kalman Filter) in a synthetic case. The results show that the parameter uncertainties are effectively reduced by incorporating observed information recursively. A comparison between PF and EnKF indicate that the results from PF are slightly better than those from EnKF. The integration shows a bright future for simulating the groundwater system in realtime. This study provides a flexible and effective approach for analyzing the uncertainties and time variant properties of the parameters and the proposed architecture of cloud computing provides a novel approach for the researchers and decision -makers to construct numerical models and follow-up researches. (C) 2017 Published by Elsevier B.V.

ABSTRACT:

Groundwater resources along the coast of Cameroon (Kribi-Campo Sub-Basin) are under siege from point and non-point pollution sources, climate change, urbanization and infrastructure development. This situation is made worse by the absence of a water management and development strategy. Managing and monitoring the area's water resources requires an understanding of the groundwater systems, and thus a thorough understanding of the geology. In this study, a 3D geological model was built from electro-seismic data and the structure of the area's aquifer system developed. The aquifer system structure was transferred into Visual MODFLOW Flex and then used to develop a typical hydrogeological model, which will help the management and monitoring of the area's groundwater resources. As more geological data become available, the current model can be updated easily by editing and recomputing. This work is expected to have a positive impact quite quickly on the provision of potable water and on public health.

ABSTRACT:

Understanding the physical, chemical and biological system is an indispensable precondition to addressing groundwater management. This understanding is based on Conceptual Hydrogeological Models, which contain different interpretations and their validity is checked through the application of specific research techniques (numerical modelling, hydrochemistry, isotope hydrology, process evaluation and biological functions). This paper describes the experience carried out by an academic team that, together with entities responsible for the protection of water resources, established strategic alliances to improve the knowledge of the hydrogeological system, providing new elements for governance. This study was carried out in the Uraba antioqueno zone, located north-west of Colombia. A complex aquifer system is located in the region, characterized by a series of permeable, semi-permeable and impermeable layers. In such a layered aquifer the determination of the physical, chemical and biological characteristics of the layers and their management are a challenge for researchers because groundwater represents a strategic resource for supplying the population and developing economic activities. Starting from the conceptual hydrogeological model, multiscale numerical modelling exercises have been carried out, enabling the characterization of local, intermediate and regional flow systems. In addition, by determining the natural background level, the concentration ranges of chemical compounds from natural sources were obtained, in order to detect future changes in water quality. It was also possible to examine the stygofauna, which allowed the recognition of different types of organisms (stygobits, stygophiles and stygoxens) associated with underground ecosystems. These scientific elements serve as a support for the management instruments such as the groundwater management plan that is important for water governance, ensuring its future sustainability.

ABSTRACT:

Kanchanapally watershed covering an area of about 11 km(2) in Nalgonda district, Andhra Pradesh, India is located in granitic terrain. Groundwater recharge has been estimated from a water balance model using hydrometeorological data from 1978-1994. The monthly recharge estimates obtained from the water balance model formed input for the groundwater flow model during transient model testing. The groundwater flow model has been prepared to simulate steady state groundwater conditions of 1977 using the nested squares finite difference method. The transient groundwater flow model has been tested during 1977-1994 using the estimated recharge values. The present study helped verify the usefulness of monthly recharge estimates for accounting dynamic variations in recharge as reflected in water level fluctuations in hydrographs.

ABSTRACT:

Bayesian inference has traditionally been conceived as the proper framework for the formal incorporation of expert knowledge in parameter estimation of groundwater models. However, conventional Bayesian inference is incapable of taking into account the imprecision essentially embedded in expert provided information. In order to solve this problem, a number of extensions to conventional Bayesian inference have been introduced in recent years. One of these extensions is 'fuzzy Bayesian inference' which is the result of integrating fuzzy techniques into Bayesian statistics. Fuzzy Bayesian inference has a number of desirable features which makes it an attractive approach for incorporating expert knowledge in the parameter estimation process of groundwater models: (1) it is well adapted to the nature of expert provided information, (2) it allows to distinguishably model both uncertainty and imprecision, and (3) it presents a framework for fusing expert provided information regarding the various inputs of the Bayesian inference algorithm. However an important obstacle in employing fuzzy Bayesian inference in groundwater numerical modeling applications is the computational burden, as the required number of numerical model simulations often becomes extremely exhaustive and often computationally infeasible. In this paper, a novel approach of accelerating the fuzzy Bayesian inference algorithm is proposed which is based on using approximate posterior distributions derived from surrogate modeling, as a screening tool in the computations. The proposed approach is first applied to a synthetic test case of seawater intrusion (SWI) in a coastal aquifer. It is shown that for this synthetic test case, the proposed approach decreases the number of required numerical simulations by an order of magnitude. Then the proposed approach is applied to a real-world test case involving three-dimensional numerical modeling of SWI in Kish Island, located in the Persian Gulf. An expert elicitation methodology is developed and applied to the real-world test case in order to provide a road map for the use of fuzzy Bayesian inference in groundwater modeling applications. (C) 2016 Elsevier B.V. All rights reserved.

ABSTRACT:

The application of the groundwater flow model SPRING to the city of Dusseldorf, Germany (217 km(2)) as part of a larger hydrological catchment area (708 km(2)) required developing a new, robust calculation scheme (RUBINFLUX) for groundwater recharge with a high spatial and temporal resolution. RUBINFLUX combines a novel approach for drainage from the unsaturated zone with proven hydrological components. The drainage is calculated as a natural exponential function using the difference between the actual storage and the water storage at field capacity without making use of the Richards equation. The simulated groundwater recharge values at each element of the groundwater mesh were used as the upper boundary condition. After transient calibration of the groundwater flow model against 871 observation wells, the transient variations of the groundwater levels at locations not influenced by river levels were accurately simulated. The integration of RUBINFLUX into SPRING has proved suitable for complex hydrological systems.

ABSTRACT:

Long-termwater resource planning requires both spatial and temporal information on groundwater recharge in order to properly manage not only water use and exploitation but also land-use allocation and development. In this context, a three-dimensional transient numerical model is developed to support management of groundwater resources and decision analysis for the coastal plain of Corinthos in Greece. Transient simulations usually are used to analyse time-dependent problems such as climate change and groundwater-level change. Among transient models, the most reliable but also the least explored, probably due to the demanding input data requirements, are the models with temporally variable recharge, also termed as fully transient models. In these models, the temporal variability of heads is dependent not only on the temporal variability of aquifer storage but also on the temporal variability of fluxes. In order to arrive at a credible set of flux data as boundary conditions for the numerical model, a sinusoidal equation is developed to simulate the missing water-level data and to forecast the future sequential records of the expected recharge. The results of the developed model reveal that at least two periodicities can be identified in the observed subsurface head-level data.

ABSTRACT:

With some 1.1 million km(2), the Guarani Aquifer System occupies most of the La Plata Basin in South America and represents one of the most important groundwater reservoirs worldwide with a storage volume of approx. 30,000 km(3). It belongs to Argentina, Brazil, Paraguay and Uruguay. Due to increasing water demands and growing risks for the groundwater quality, a multinational project for the protection and sustainable use of this groundwater reserve was implemented by the World Bank. Between 2003 and 2009, the project was executed by the Organization of American States. The German Federal State Geological Survey (BGR) was also involved in the overall work and provided support to Paraguay by analyzing the Guarani Aquifer System in Paraguay. A numerical model was developed to characterize groundwater flow in the Guarani Area of Paraguay and neighbouring regions in Argentina and Brazil, and is being used to quantify groundwater exchange.

ABSTRACT:

Ongoing developments in geological and hydrogeological investigation techniques, especially direct-push methods, have led to an increase in the quality, density and spatial resolution of data available from such investigations. This has created new challenges in the development of numerical models in terms of accurately and efficiently translating detailed and complex conceptual models into effective numerical models. Suitable geometrical and numerical modelling tools are essential in order to meet these challenges. This paper describes the development of a three-dimensional hydrogeological flow model for a contaminated site near Berlin, Germany, based on high-resolution geological data obtained principally using direct-push methods. The available data were first interpreted to construct a detailed GIS-based geological model, which formed the basis of the conceptual site model. The conceptual model was then translated into a geometrical model, which was used to create a finite element numerical model. An innovative geometry object-based approach enabled the complex structural details of the conceptual model to be accurately reproduced in the numerical model domain. The resulting three-dimensional steady-state unconfined flow model was successfully calibrated using external automated calibration software, whereby parameter values for groundwater recharge and hydraulic conductivity were determined.

ABSTRACT:

Arsenic contaminated shallow aquifers evaluation, mitigation, and management strategies are the challenging task to all the hydrologist and provide a safe drinking water demand in the Holocene age, alluvial aquifers. To manage and mitigate such problems, we used numerical groundwater modeling software (GMS 10.2), for the development of 3D transient state predictive (groundwater flow and contaminant transport) conceptual model for two topographically different arsenic contaminated regions. The models were built by using the measured hydro-geological data, empirical values, and equations. Groundwater flow calibration, sensitivity analyses, and validation were performed for each soil parameters, varying boundary conditions and for alternate meteorological scenarios. The MODFLOW results suggested that, the distribution of As contaminant was directly controlled by the complex hydrostratigraphy, surface water bodies and indirectly controlled by the change in meteorological conditions. The MT3DMS model, for As contaminant transport, used for the assessment of shallow and deeper aquifers. The results showed that the downward movement of As has made the deeper aquifer unsafe for drinking water and irrigation purposes. However, the aquifers and regions with high flushing capability, negligible vertical hydraulic conductivity can be delineated as As safe groundwater source, irrespective of their sediment color. Therefore, for the geogenic source of As, both the simulation results inferred that to estimate and mitigate As contaminant groundwater aquifers or regions, the numerical modeling solution is a technically viable means an effective decision-making tool.

ABSTRACT:

The joint project SeeZeichen deals with essential immission pathways of water constituents into Lake Constance. A wide variety of measuring concepts, measuring instruments, and numerical models have been combined with each other in order to achieve a comprehensive representation of the entry of groundwater into Lake Constance. Based on a catchment-wide hydrogeological model, a groundwater model for the Lake Constance region was implemented, which for the first time calculates temporally differentiated and spatially highly-resolved quantitative estimates of groundwater inflows into Lake Constance. With a method toolbox for identifying and quantifying groundwater in lakes, groundwater exfiltration into Lake Constance can be localized and quantified. A multi-parameter water body signature allows to obtain further information on groundwater inflows into the lake. The measured values obtained were interpreted and checked for their plausibility by means of inverse modeling with a spatially high-resolution 3-dimensional hydrodynamic lake model. With a coupled groundwater-lake model, the entire system of hydrogeological context/groundwater and lake can be seamlessly modeled for the first time. Measuring methods, tools and models are also used in Lake Ammersee and Lake Steisslinger See, thus demonstrating the transferability to other lakes and into the general water management practice.

ABSTRACT:

We present a general and flexible Bayesian approach using uncertainty multipliers to simultaneously analyze the input and parameter uncertainty of a groundwater flow model with consideration of the heteroscedasticity of the groundwater level error. Groundwater recharge and groundwater abstraction multipliers are introduced to quantify the uncertainty of the spatially distributed input data of the groundwater model in addition to parameter uncertainty. The heteroscedasticity of the groundwater level error is also considered in our Bayesian approach by incorporating a new heteroscedastic error model. The proposed methodology is applied in an overexploited aquifer in Bangladesh where groundwater abstraction and recharge data are highly uncertain. The results of the study confirm that consideration of recharge and abstraction uncertainty through the use of recharge and abstraction multipliers is feasible even in a fully distributed physically based groundwater flow model. Heteroscedasticity is present in the groundwater level error and has an effect on the model predictions and parameter distributions. The input uncertainty affects the model predictions and parameter distributions and it is the dominant source of uncertainty in the groundwater flow prediction. Additionally, the approach described also provides a new way to optimize the spatially distributed recharge and abstraction data along with the parameter values under uncertain input conditions. We conclude that considering model input uncertainty along with parameter uncertainty and heteroscedasticity of the groundwater level error is important for obtaining realistic model predictions and a correct estimation of the uncertainty bounds.

ABSTRACT:

The fact that dependent variables of groundwater models are generally nonlinear functions of model parameters is shown to be a potentially significant factor in calculating accurate confidence intervals for both model parameters and functions of the parameters, such as the values of dependent variables calculated by the model. The Lagrangian method of Vecchia and Cooley [Vecchia, A.V. & Cooley, R.L., Water Resources Research, 1987, 23(7), 1237-1250] was used to calculate nonlinear Scheffe-type confidence intervals for the parameters and the simulated heads of a steady-state groundwater flow model covering 450 km(2) of a leaky aquifer. The nonlinear confidence intervals are compared to corresponding linear intervals. As suggested by the significant nonlinearity of the regression model, linear confidence intervals are often not accurate. The commonly made assumption that widths of linear confidence intervals always underestimate the actual (nonlinear) widths was not correct. Results show that nonlinear effects can cause the nonlinear intervals to be asymmetric and either larger or smaller than the linear approximations. Prior information on transmissivities helps reduce the size of the confidence intervals, with the most notable effects occurring for the parameters on which there is prior information and for head values in parameter zones for which there is prior information on the parameters. (C) 1999 Elsevier Science Ltd. All rights reserved.

ABSTRACT:

Study region: Four districts (Meinong, Qishan, Dashu, and Daliao) of Kaohsiung city, Southern Taiwan & nbsp;Study focus: The understanding of aquifer recharge in terms of water table response to rainfall is of critical importance to groundwater systems management and various endeavors have been made to estimate the amount of recharge using rainfall data. The purpose of this study is to evaluate the groundwater level response to rainfall and determine the recharge potential for shallow aquifers. We showed a simple approach to estimate specific yield (Sy) and hydraulic conductivity (k) as functions of rainfall and water level data.& nbsp;New hydrological insights for the region: Correlation method is applied to investigate groundwater level response to associated rainfall and it was found that the rise in water table linearly depends on the rainfall amount per event. Results show the annual recharge rates of 244-1472 mm year1, which represent 12-43% of rainfall in the study area. The estimated k (order of 10(4) to 10(5) m s(-1)) and S-y (0.20-0.51) were used as prior values to setup groundwater numerical modeling using WASH123D. The real-time case scenario simulation using pumping and rainfall data indicated the reasonable hydrological response of groundwater levels to rainfall. The long-term simulations should be performed with WASH123D to deal with the subjectivity of sustained groundwater pumping and sustainability of aquifers for better groundwater resource planning and management.

ABSTRACT:

Process-based groundwater models are useful to understand complex aquifer systems and make predictions about their response to hydrological changes. A conceptual model for evaluating responses to environmental changes is presented, considering the hydrogeologic framework, flow processes, aquifer hydraulic properties, boundary conditions, and sources and sinks of the groundwater system. Based on this conceptual model, a quasi-three-dimensional transient groundwater flow model was designed using MODFLOW to simulate the groundwater system of Mahanadi River delta, eastern India. The model was constructed in the context of an upper unconfined aquifer and lower confined aquifer, separated by an aquitard. Hydraulic heads of 13 shallow wells and 11 deep wells were used to calibrate transient groundwater conditions during 1997-2006, followed by validation (2007-2011). The aquifer and aquitard hydraulic properties were obtained by pumping tests and were calibrated along with the rainfall recharge. The statistical and graphical performance indicators suggested a reasonably good simulation of groundwater flow over the study area. Sensitivity analysis revealed that groundwater level is most sensitive to the hydraulic conductivities of both the aquifers, followed by vertical hydraulic conductivity of the confining layer. The calibrated model was then employed to explore groundwater-flow dynamics in response to changes in pumping and recharge conditions. The simulation results indicate that pumping has a substantial effect on the confined aquifer flow regime as compared to the unconfined aquifer. The results and insights from this study have important implications for other regional groundwater modeling studies, especially in multi-layered aquifer systems.

ABSTRACT:

Coastal delta plains are areas with high agricultural potential for the Mediterranean region because of their high soil fertility, but they also constitute fragile systems in terms of water resources management because of the interaction of underlying aquifers with the sea. Such a case is the Pinios River delta plain located in central Greece, which also constitutes a significant ecosystem. Soil and Water Assessment Tool (SWAT) and SEAWAT models were combined in order to simulate the impact of current water resources management practices in main groundwater budget components and groundwater salinization of the shallow aquifer developed in the area. Moreover, potential climate change impact was investigated using climate data from Regional Climate Model for two projected periods (2021-2050 and 2071-2100) and two sea level rise scenarios (increase by 0.5 and 1 m). Modeling results are providing significant insight: although the contribution of the river to groundwater inflows is significant, direct groundwater recharge from precipitation was found to be higher, while capillary rise constitutes a major part of groundwater outflows from the aquifer. Moreover, during the simulation period, groundwater flow from the aquifer to the sea were found to be higher than the inflows of seawater to the aquifer. Regarding climate change impact assessment, the results indicate that the variability in groundwater recharge posed by the high variability of precipitation during the projected periods is increasing the aquifer's deterioration potential of both its quantity and quality status, the latter expressed by the increased groundwater Cl- concentration. This evidence becomes more significant because of the limited groundwater storage capacity of the aquifer. Concerning sea level rise, it was found to be less significant in terms of groundwater salinization impact compared to the decrease in groundwater recharge and increase in crop water needs.

ABSTRACT:

The coastal population of Bangladesh has already been suffering from the salinity encroachment both in groundwater and surface water regime. Reduced river discharge, coastal surges, shrimp farming, lowering of groundwater table due to dry season irrigation in a large part of the country accelerate the rate of saline water distribution. In addition, sea level rise, due to the impact of climate change, may contribute to salinity encroachment on coastal freshwater resources, particularly in the shallow alluvial aquifers. Though the groundwater table is within 2-5 m below ground surface, availability of fresh and safe water in the coast is very limited in upper aquifers because of the arsenic contamination and water salinity. For the coastal population, deep (>250 m) tube wells are the main source of drinking water and irrigation water supply is mostly restricted to surface water including rainwater. In monsoon, freshwater pockets are available at the shallow depth (<8 m) from seasonal precipitation but mostly turn to brackish condition during dry period. Therefore, assessment and monitoring of development stress and probable impact of climate change on freshwater resource are utmost important. The main purpose of the study is to assess the impact of climate change and development stresses on the availability of fresh water resources in the coastal area. For that purpose, integrated hydrological model has been prepared describing the subsurface condition both the saturated and unsaturated zone together with the influence of various water components of the hydrological cycle. Groundwater salinity models are developed to simulate salinity transport in the sea, river and through the porous medium of aquifer for a range of existing and possible future conditions. It has been seen from the simulation result of the model that under climate change condition during the month of March and April, the salinity level is highest for all river system within the study area and significant during period from December to June. The climate change scenario illustrates that the groundwater level increases within the range of 0.6-0.8 m under climate change scenario. Movement of salinity is found insignificant from the river to the aquifer. Major rivers in the south central coast there is a considerable interaction between surface water and groundwater due to the tidal effect. On the other hand, there is negligible interaction between the aquifer and adjacent river in the south-eastern coastal plain.

ABSTRACT:

The coastal population of Bangladesh has already been suffering from the salinity encroachment both in groundwater and surface water regime. Reduced river discharge, coastal surges, shrimp farming, lowering of groundwater table due to dry season irrigation in a large part of the country accelerate the rate of saline water distribution. In addition, sea level rise, due to the impact of climate change, may contribute to salinity encroachment on coastal freshwater resources, particularly in the shallow alluvial aquifers. Though the groundwater table is within 2-5 m below ground surface, availability of fresh and safe water in the coast is very limited in upper aquifers because of the arsenic contamination and water salinity. For the coastal population, deep (>250 m) tube wells are the main source of drinking water and irrigation water supply is mostly restricted to surface water including rainwater. In monsoon, freshwater pockets are available at the shallow depth (<8 m) from seasonal precipitation but mostly turn to brackish condition during dry period. Therefore, assessment and monitoring of development stress and probable impact of climate change on freshwater resource are utmost important. The main purpose of the study is to assess the impact of climate change and development stresses on the availability of fresh water resources in the coastal area. For that purpose, integrated hydrological model has been prepared describing the subsurface condition both the saturated and unsaturated zone together with the influence of various water components of the hydrological cycle. Groundwater salinity models are developed to simulate salinity transport in the sea, river and through the porous medium of aquifer for a range of existing and possible future conditions. It has been seen from the simulation result of the model that under climate change condition during the month of March and April, the salinity level is highest for all river system within the study area and significant during period from December to June. The climate change scenario illustrates that the groundwater level increases within the range of 0.6-0.8 m under climate change scenario. Movement of salinity is found insignificant from the river to the aquifer. Major rivers in the south central coast there is a considerable interaction between surface water and groundwater due to the tidal effect. On the other hand, there is negligible interaction between the aquifer and adjacent river in the south-eastern coastal plain.

ABSTRACT:

of groundwater by precipitation is low. Numerical modelling is a helpful tool in the assessment of groundwater resources and analysis of future exploitation scenarios. To quantify the groundwater resources of the East Owienat area in the southwest of the Western Desert, Egypt, the present study assesses the groundwater resources management of the Nubian aquifer. Groundwater withdrawals have increased in this area, resulting in a disturbance of the aquifer's natural equilibrium, and the large-scale and ongoing depletion of this critical water reserve. Negative impacts, such as a decline in water levels and increase in salinity, have been experienced. The methodology includes application of numerical groundwater modelling in steady and transient states under different measured and abstraction scenarios. The numerical simulation model developed was applied to assess the responses of the Nubian aquifer water level under different pumping scenarios during the next 30 years. Groundwater management scenarios are evaluated to find an optimal management solution to satisfy future needs. Based on analysis of three different development schemes that were formulated to predict the future response of the aquifer under long-term water stress, a gradual increase in groundwater pumping to 150% of present levels should be adopted for protection and better management of the aquifer. Similar techniques could be used to improve groundwater management in other parts of the country, as well as other similar arid regions.

ABSTRACT:

A three-dimensional fractured medium flow model was developed for the Bear Creek Valley (BCV) S-3 site of the Oak Ridge Reservation (ORR) using SWIFT III. The numerical modeling for this site focused on a conceptual model established through the analysis of heterogeneous geologic units and matrix fracture properties of the subsurface in the BCV area. The SWIFT III modeling analysis was based on the previous modeling studies that used MODFLOW and MODPATH. A rigorous calibration was obtained first by comparing simulated results with the existing data on ground water levels and then by comparing pumping test results with the simulated ground water levels. A satisfactory agreement between observed and simulated results was obtained. The calibrated model was used to determine sustained yield from a ground water interceptor trench. Different withdrawal rates were used to simulate the performance of the trench for the sustained withdrawal of ground water.

ABSTRACT:

Pumping optimization of coastal aquifers involves complex numerical models. In problems with many decision variables, the computational burden for reaching the optimal solution can be excessive. Artificial Neural Networks (ANN) are flexible function approximators and have been used as surrogate models of complex numerical models in groundwater optimization. However, this approach is not practical in cases where the number of decision variables is large, because the required neural network structure can be very complex and difficult to train. The present study develops an optimization method based on modular neural networks, in which several small subnetwork modules, trained using a fast adaptive procedure, cooperate to solve a complex pumping optimization problem with many decision variables. The method utilizes the fact that salinity distribution in the aquifer, depends more on pumping from nearby wells rather than from distant ones. Each subnetwork predicts salinity in only one monitoring well, and is controlled by relatively few pumping wells falling within certain control distance from the monitoring well. While the initial control area is radial, its shape is aclaptively improved using a Hermite interpolation procedure. The modular neural subnetworks are trained adaptively during optimization, and it is possible to retrain only the ones not performing well. As optimization progresses, the subnetworks are adapted to maximize performance near the current search space of the optimization algorithm. The modular neural subnetwork models are combined with an efficient optimization algorithm and are applied to a real coastal aquifer in the Greek island of Santorini. The numerical code SEAWAT was selected for solving the partial differential equations of flow and density dependent transport. The decision variables correspond to pumping rates from 34 wells. The modular subnetwork implementation resulted in significant reduction in CPU time and identified an even better solution than the original numerical model. (C) 2009 Elsevier Ltd. All rights reserved.

ABSTRACT:

This paper presents the analysis of a regional groundwater model via Feflow in tropical regions using two techniques: pilot points (PP) and constant zones (CZ). These methodologies allow the proper identification of biased parameters and heterogeneities of hydraulic properties. For this purpose, we developed a numerical density-variable model that is limited to reinterpreted data from real measurements. For the CZ, the initial parameters are considered constant; in contrast, in the PP technique, the initial parameters are assigned according to interpolations using in-situ point measurements. The developed model was applied in an area under the influence of the Inter-tropical Convergence Zone, located in the middle valley of Magdalena (MMV). This area is important in the development of Colombia due to its contribution to Gross Domestic Product, and it has been subject to significant changes in land use, as a result of intense economic activities. The established model shows a link between the observed state variable (hydraulic head) and hydraulic conductivity (K) proving the importance of spatial heterogeneity in K. The model is calibrated in order to establish K, the porosity and the specific storage capacity, reducing the mean square error of the state variable dependable on the observation points. The results show that the PP system approach provides a better heterogeneity representation and shows that each parameter is sensitive, and does not depend on other parameters. This research compiles the first breakthrough toward a methodology to assertively restrict a highly parameterized inverse regional model in a tropical basin.

ABSTRACT:

The Chennai aquifer system, which occupies an area of 6629 km(2), is one of the most stressed aquifer systems in southern India and is under severe threat of over exploitation and quality deterioration. This is due to the increasing groundwater abstraction for irrigation, domestic, industrial purposes and for drinking water supply to the ever-expanding Chennai city. To offset the effect of this heavy extraction a paradigm shift towards groundwater management was imperative. A multidisciplinary integrated approach was used to map the aquifers, delineate their geometry, to determine the hydraulic behavior of the aquifer system, and to formulate an aquifer management plan through the development of a groundwater flow model. The main aquifers in the area include weathered and fractured crystalline rocks and recent alluvial formation. Alluvium is the most significant aquifer system in the study area, and this aquifer contains potable quality groundwater except in the eastern part of the study area that has been affected by seawater intrusion. A two-layered groundwater flow model was developed using Visual MODFLOW classic version 4.6 with a 1 km(2) grid pattern to simulate groundwater flow for a period of 9 years. The model was calibrated under steady and transient state conditions and allowed components of the water balance of the system to be determined at a regional scale. The simulated results indicate that this aquifer system is under tremendous stress at the prevailing groundwater withdrawal rate of 899 million cubic meter (mcm)/year and would become unstable with the predicted 25% increase in groundwater withdrawal by 2025. However, the interventions to recharge an additional 54 mcm of water could help mitigate the current decline in potentiometric heads and could partially help to arrest the further advancement of seawater intrusion. A scenario of maintaining flow in rivers for a period of 120 days each year coupled with the construction of an unlined canal shows increase in groundwater head and development of the groundwater mounds, which are positive signs for arresting the decline of the water table and pushing saline groundwater in a seaward direction. As a result of the high rate of groundwater depletion in the area, management strategies need to be implemented urgently in the region. These strategies should include the regulation of groundwater abstraction and maintaining an extended flow period in the rivers. These measures are required to improve the sustainability of the available groundwater resources of the region.

ABSTRACT:

Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater. This study presents the development of a conceptual and numerical model for the coastal aquifer of Karareis region (Karaburun Peninsula) in the western part of Turkey. The study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers. The SEAWAT model is used in this study to solve the density-dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months. The model was calibrated using the average values of a 1-year dataset and further verified by the average values of another year. Five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years. The result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under "increased pumping" scenario, while a slight change in water level and TDS concentrations was observed in " climate change" scenario. Results also revealed that a reduction in the pumping rate from Karareis wells will be necessary to protect fresh groundwater from contamination by seawater.

ABSTRACT:

A three-dimensional mathematical model to simulate regional groundwater flow was used in the lower Palar River basin, in southern India. The study area is characterised by heavy abstraction of groundwater for agricultural, industrial and drinking water supplies. There are three major pumping stations on the riverbed apart from a number of wells distributed over the area. The model simulates groundwater flow over an area of about 392 km(2) with 70 rows, 40 columns, and two layers. The model simulated a transient-state condition for the period 1991-2001. The model was calibrated for steady- and transient-state conditions. There was a reasonable match between the computed and observed heads. The transient model was run until the year 2010 to forecast groundwater flow under various scenarios of overpumping and less recharge. Based on the modelling results, it is shown that the aquifer system is stable at the present rate of pumping, excepting for a few locations along the coast where the groundwater head drops from 0.4 to 1.81 m below sea level during the dry seasons. Further, there was a decline in the groundwater head by 0.9 to 2.4 m below sea level in the eastern part of the area when the aquifer system was subjected to an additional groundwater withdrawal of 2 million gallons per day (MGD) at a major pumping station.

ABSTRACT:

Oil exploration and development have taken place extensively in the near-shore waters of the Bay of Bengal for over two decades, with onshore coastal aquifers serving as a primary source of water injected into near-shore production wells for enhanced oil recovery. Field and modeling studies were initiated to assess the effects of potential seawater intrusion into the coastal aquifers and to improve strategies for groundwater development and management. Groundwater levels were measured at 42 locations in the central Godavari delta (295 km(2)) over a period of 2 years (2006-2007). These data indicated that the predominant groundwater flow direction consistently points toward the coast with no significant change in groundwater table elevations during the study period. Groundwater samples analyzed for major ions revealed the groundwater to be brackish in nature with an average salinity of similar to 5,000 mg L-1. A numerical model of variable density, groundwater flow, and solute transport (SEAWAT) was developed for the study region. After calibrating against observed hydraulic head data for the year 2006 at steady state, the model was used to predict the extent of seawater intrusion in the study area over the next 50 years. The estimated regional groundwater budget indicates a significant amount of groundwater outfall to the Bay of Bengal. The model predicts that the area will not be affected by seawater intrusion at the present rate of groundwater exploitation near the coast.

ABSTRACT:

Conceptual geological models of industrial and mining megasites ire all essential task of groundwater investigations as well as environmental risk assessment studies. Therefore, the conceptualization process of the structural geological model has depended oil the development of,I set of 2D cross-sections to portray a 3D picture of groundwater flow. This attempt always includes some simplifications that require, only to some extent, the true 3D situation of heterogeneous aquifers. Consequently, the modelled predictions of the path flow and transport conditions of contaminated groundwater are not satisfying in terms of a flow-path and risk based modelling approach. A more structured approach to develop the hydrogeological framework for the conceptual model is advocated, using different 3D geological modelling software packages to assemble the data, working in three dimensions and using this platform for subsequent groundwater flow modelling. Attention is given to the capability of different 3D modelling approaches, indicated by geostatistically based versus constructive cross-section based interpolations of complex sedimentary successions, that are compared in their results and suitability for subsequent hydrogeological modelling requirements. The paper describes the results, in high-resolution 3D modelling, of the complex geological environment of the Bitterfeld/Wolfen megasite in the eastern part of Germany. Identification, assessment, and remediation of large-scale groundwater contamination require a detailed knowledge of the heterogeneous geological structure to predict the fate and pathways of contaminants and their potential interaction with, e.g., surface water. An area of 16 kill 2 of the model area of the Bitterfeld/Wolfen area was chosen to transfer the complex structural geological setting. The subsurface geology could be assigned to 31 lithostratigraphic units and depicted using a 10 x 10m GIS grid. This constructive and knowledge-driven 3D modelling allows the prediction of vertical and horizontal Sections, Visualization purposes, volumetric calculations of distinct sedimentary units, GIS applications, and the use of the detailed digital information within the subsequent flow and transport groundwater modelling. The high-resolution digital 3D model improves the hydrogeological modelling results. It is considered a basic requirement for groundwater modelling and investigations on environmental risk and impact assessment by fate and pathway exposure route analysis of the complex geological and groundwater situations. (C) 2007 Elsevier Ltd. All rights reserved.

ABSTRACT:

The management of coastal aquifers requires careful planning of withdrawal strategies for control and remediation of saltwater intrusion. Over exploitation of groundwater in coastal aquifers may result in intrusion of saltwater. Prediction and control of future saltwater distribution in coastal aquifer may be possible by simulating the processes with utilizing mathematical models. The groundwater resources in North Sinai area are affected by salt water up-coming due to over-pumping phenomenon beside seawater intrusion. The objective of this study was to apply mathematical modeling techniques for water resource management in salt-affected ecosystems. The study area is located in the northern coastal zone of Sinai Peninsula of Egypt and covers about 1750 km(2). The methodological approach to simulate the groundwater flow is based on the mathematical modeling techniques with applying 3-D finite element software (FEFLOW model). Three management scenarios are applied to predict the drawdown of groundwater levels under different extraction rates and seawater intrusion phenomenon. In addition, the methodology of seawater intrusion study and calibration was based on applying two-dimensional finite element simulation (SWI) code. The results of ground-water flow simulation show optimum groundwater extractions 26 x 10(6) m(3)/year from the cultivated areas. Moreover, simulation results indicate that the seawater/freshwater interface will migrate, after 15 years, at the distance of 5.5 km landward from its initial position if the present groundwater production policy (19 x 10(6) m(3)/year) continues operating in the area. To conserve the Quaternary Aquifer in North Sinai coastal Area (QANSA) storage for longer time, it is recommended to reduce the number of the pumping wells (<300 wells) as well as the initial and running time (does not exceed 10 h), and to achieve the objective of implementing the developing policy without any increase (500 m(3)/day/well). It is highly recommended to carry out geophysical exploration study and to construct monitoring network to verify the results of the applied model.

ABSTRACT:

Jeju Island is the largest island in South Korea. Recently, extensive groundwater abstraction has been reported from the shallow aquifer in the northeast region of the island. This study simulated the freshwater resources of the aquifer to estimate the sustainability of groundwater use on Jeju Island in terms of its vulnerability to seawater intrusion. Three-dimensional finite-difference numerical groundwater models were simulated using the MODFLOW-family code SEAWAT. Precise and recent groundwater level and multi-depth salinity data obtained from the study site were used for model calibration; the simulated results showed good agreement with the observed data. SEAWAT was used to delineate the current seawater-freshwater interface to quantitatively estimate the coastal fresh groundwater resources. Future stress scenarios were also simulated in response to increased pumping and various changes in the recharge. The results showed that current groundwater use in the coastal aquifer did not induce seawater intrusion in the coastal aquifer, but seawater intrusion will occur if the dry season continues for the next ten years. The vulnerability assessment based on the predicted groundwater levels and ion concentrations using numerical simulations suggests future vulnerability in the aquifer; therefore, continuous assessment and visualization of the aquifer sustainability is vital. Future projections by the integrated SEAWAT simulation and GALDIT assessment showed that an increase in groundwater pumping may escalate the vulnerability status of coastal groundwater resources from moderate to high in some areas of the study site, by inducing lateral seawater intrusion in deeper areas of the unconfined aquifer.

ABSTRACT:

Using numerical models, it is possible to predict with the governing process or different management scenarios, how the aquifer reacts to abstraction and recharge. In this study, the hydraulic behavior of Varamin Plain aquifer was simulated using the MODFLOW code of GMS software. The main aim of this simulation is to evaluate the effect of current aquifer management plans and the Jajrood River basin on changes in the water table of the unconfined aquifer and the piezometric level of the confined aquifer. After calibrating the model, the hydrodynamic coefficients were corrected and then using the obtained model, the quantitative behavior of the aquifer was predicted for two management scenarios for the future years. The results of the study showed that the implementation of recharge and discharge management plans can only lead to a decrease in groundwater level in the aquifer if it does not significantly reduce the percentage of water entering the aquifer. (C)2020 INT TRANS J ENG MANAG SCI TECH.

ABSTRACT:

The conceptual hydrogeological model of the study area is generalized according to the hydrogeological conditions, and then the numerical model of groundwater flow is built by MODFLOW-2000. Under current condition of groundwater exploitation, the groundwater flow field in the year 2018 of the study area is forecasted. The result shows the groundwater level will decrease in the river valley of Jixi City, and drainage of local aquifer occurs in the lower reach of Muling River Valley. The numerical model provides a significant scientific basis for sustainable utilization of groundwater resources in Jixi City.

ABSTRACT:

One of the objectives of groundwater numerical modeling is to accurately reproduce the flow velocity field and the flow and transport pathways. In this article the hydro-stratigraphic dataset, used in the co-submitted article "Modeling the interference of underground structures with groundwater flow and remedial solutions in Milan"(De Caro et al., 2020) [1], is presented. The work aims to reconstruct the spatial variability of the hydraulic parameters in the shallow aquifers of the Milan City area (northern Italy) and to integrate them in a groundwater flow 3D finite element method (FEM) numerical model. This objective is achieved by converting qualitative borehole logs stratigraphic information into hydrogeological parameters (e.g. hydraulic conductivity and porosity) and by interpolating these parameters over the finite element mesh nodes by means of 3D kriging techniques. The modeling domain and the mesh nodes, the boundary surfaces between the aquifers as well as some of the piezometric data used to calibrate the model are presented to make the numerical experiment reproducible. (c) 2020 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

ABSTRACT:

A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved groundwater resource management.

ABSTRACT:

Groundwater models provide an efficient means to evaluate the sustainability of new groundwater production wells. An important component of any groundwater modeling analysis is the quantification of the prediction uncertainty. This analysis incorporates uncertainty analysis techniques within the groundwater modeling environment to predict regions within a groundwater basin that have a low probability of excessive drawdown and groundwater contamination. The analysis focuses on the quantification of a basin-wide water-balance, generation of a spatial distribution of lithology, locating a nearby total dissolved solids (TDS) plume, and construction of an accurate groundwater flow model. Thousands of Monte Carlo realizations are simulated to determine the most probable parameter sets based on an objective function that minimizes the error between simulated and observed hydraulic head. Only those simulations with small error are used in a subsequent analysis to investigate 77 potential well locations near the city of Fernley, in northern Nevada. The final result is a map depicting the probability that a production well has either excessive drawdown and/or encroachment of the TDSs plume. (c) 2004 Elsevier B.V. All rights reserved.

ABSTRACT:

A conduit flow process (CFP) for the Modular Finite Difference Ground-Water Flow model, MODFLOW-2005, has been created by the U. S. Geological Survey. An application of the CFP on a carbonate aquifer in southern Florida is described; this application examines (1) the potential for turbulent groundwater flow and (2) the effects of turbulent flow on hydraulic heads and parameter sensitivities. Turbulent flow components were spatially extensive in preferential groundwater flow layers, with horizontal hydraulic conductivities of about 5,000,000 m d(-1), mean void diameters equal to about 3.5 cm, groundwater temperature equal to about 25 degrees C, and critical Reynolds numbers less than or equal to 400. Turbulence either increased or decreased simulated heads from their laminar elevations. Specifically, head differences from laminar elevations ranged from about -18 to +27 cm and were explained by the magnitude of net flow to the finite difference model cell. Turbulence also affected the sensitivities of model parameters. Specifically, the composite-scaled sensitivities of horizontal hydraulic conductivities decreased by as much as 70% when turbulence was essentially removed. These hydraulic head and sensitivity differences due to turbulent groundwater flow highlight potential errors in models based on the equivalent porous media assumption, which assumes laminar flow in uniformly distributed void spaces.

ABSTRACT:

A finite-difference ground-water flow model linked to a particle-tracking routine was used to determine ground-water flow paths and residence times in the Cambrian-Ordovician sandstone aquifer of eastern Wisconsin. The modeled region was a cross section along an approximate flow line that included the boundary between unconfirmed and confined conditions in the aquifer. Modeling results indicate that lower conductivity units within the sandstone aquiter produce vertically stratified flow in the confined region. These simulation results help explain chemical signatures of ground water in different parts of the aquifer. Three distinct regions of the flow system are identified: the unconfined zone where vertical mixing across the aquifer yields a homogeneous chemistry, the shallow part of the confined zone where sodium and sulfate charged water from the Maquoketa Shale mixes with water that has migrated from the unconfined area, and the deeper region of the confined aquifer, containing older water that entered the system in the unconfined area. Radium activities in ground water increase with distance along flow paths predicted by the simulation, consistent with a low concentration source of solid phase uranium and release of decay products to ground water by desorption and dissolution throughout the sandstone aquifer.

ABSTRACT:

Numerical models have been an integral component in management of the Edwards Aquifer for over four decades. The scale and complexity of the models have varied considerably during this time, with the changes attributed to improvements in both numerical software and the conceptual models on which the models are predicated. Resolution of early models was coarse, which rendered them useful only in large-scale, groundwater-resource assessments. Increased resolution and improved refinement in the conceptualization of the complex hydrostratigraphic framework of the Edwards Aquifer have led to expanded applicability of the ensuing models in terms of accommodating local-scale hydraulic features such as pumping scenarios and changes in recharge/discharge mechanisms (i.e., urbanization and climate change). As part of these improvements and advancements, regional-scale groundwater availability models augmented by local-scale models based upon improved conceptualization provide the ability to: (1) replicate more extreme conditions, such as the drought-of-record; (2) improve boundary conditions by extending models to include natural hydraulic boundaries; and (3) couple groundwater flow models with surface-water flow models so that the entire terrestrial water cycle can be accommodated during water-resource management scenario assessment.

ABSTRACT:

Over the last years the sustainable management of coastal water resources has become strategic, especially in southern Salento Peninsula (Apulia), where mal-performing management strategies adopted, together with the vulnerability of the hydrogeological system, have given rise to the deterioration of groundwater quality due to saltwater intrusion. In the study area there is the presence of multilevel shallow aquifer and a deep aquifer that interact by means of faults. The geological system is highly vulnerable to seawater intrusion so there is the need to adopt management strategies to avoid seawater intrusion phenomena. Nevertheless there is a lack of studies that analyze the methodology for the correct exploitation if the water resource in order to avoid further intrusion phenomena. This paper combines a density-driven, flow numerical model (Seawat v. 4) with a fault conceptual and hydrologic model to simulate saltwater intrusion phenomenon in the deep as well as in the shallow aquifer of the Salento area. By means of the individuation of an indicator parameter of groundwater quality, it has been possible to simulate different scenarios of exploitation and therefore to define critical stress scenarios for both aquifers. The results show that the deep aquifer is more vulnerable than the shallow one, which means that in the former, in order not to reach conditions of contamination, a lower density of wells is necessary than in the latter. The reduction of well density coupled with the artificial recharge of freshwater into the aquifer may be proposed as a solution strategy to protect the aquifer. Therefore, future developments of the present study will be represented by the simulation of different scenarios of recharging to inhibit the saltwater intrusion front further inland. The proposed methodology and its future developments can represent an empirical tool to provide preliminary guidelines for long-term groundwater management in coastal aquifers.

ABSTRACT:

Seawater intrusion into coastal aquifers is a major problem in almost all parts of the world. The increasing demand for fresh water in coastal regions is being met by the coastal aquifers. The development and management of fresh groundwater resources in coastal aquifers are seriously constrained by the presence of seawater intrusion. For proper management of coastal aquifers, it is necessary to assess the extent of saltwater intrusion in the aquifers. In the present study a numerical model based on solute transport, which can simulate seawater intrusion, is studied and is applied to an actual field situation. The extent and pattern of seawater intrusion in the region is simulated under the present situation. Simulations are also carried out to find the effect of pumping rate on the intrusion pattern in the vertical direction. The model is applied to an actual field problem. The model is calibrated in steady state to estimate model parameters such as conductivity and specific yield. Simulation runs are performed for the model to calculate groundwater heads in the region for a period of 180 days. When these heads are compared with the observed heads it yields a correlation coefficient of 0.75. The model is then calibrated in the transient state and when the transient heads are compared with observed heads a correlation coefficient of 0.98 is obtained. The model is then applied to simulate seawater intrusion in the horizontal direction. It is seen that the advancement of the seawater intrusion front is at maximum for a depth of 28-40m from the ground surface. The simulation is also carried out to see the effect of the pumping rate on the advancement of the seawater intrusion front in the vertical direction in the region along the three pumping wells namely Karichal, Pollinkudi and Adimalathura. The rate of advancement in the intrusion front in the Pollinkodi pump well is found to be greater than the other pumping wells.

ABSTRACT:

Water scarcity in urban areas is a common problem in many cities of India, and Visakhapatnam, a fast growing industrial city on the east coast of India, is no exception. Increasing urban population, industrial expansion and shrinking surface-water sources have widened the gap between the demand and supply, resulting in groundwater depletion and saline water intrusion along the coastal region. MODFLOW is a widely used numerical groundwater flow model but requires realistic estimation of field inputs in order to contribute effectively to recommendations for proper management actions. The present study focuses on computing the spatial and temporal variations of model inputs such as pumping and recharge rates using the field data collected from various organizations. The developed PMWIN MODFLOW model provides insight into the present and future trends in the variation of groundwater levels. Observation wells data are used in the model calibration to fix the aquifer parameters through the parameter estimation algorithm PEST. Models are performed for four projected scenarios with different rates of pumping and recharge values. Results indicate the importance of improving the recharge capability of potential areas, to sustain the aquifer's capacity to cope with stresses on groundwater resources. The model results are useful to fix optimum pumping limits in the study area for sustainable groundwater management and will help to prevent disastrous impacts on groundwater potential in the future.

ABSTRACT:

Sustainable groundwater aquifers are critical in arid and semiarid countries due to the scarcity of surface water and precipitation. Management of groundwater resources requires estimation of aquifer properties and interaction between multilayers in heterogeneous aquifers. A three-dimensional groundwater flow model was implemented to simulate a complex multilayer aquifer in Oman. Steady-state model was calibrated using groundwater level data in July 2016. Both the automated parameter calibration technique and manual trial and error method were applied for calibrating hydraulic conductivity, groundwater recharge, and anisotropy of soil layers. The optimum set of parameters of 14 observation wells was obtained from the simulation with minimum root mean square error of 0.8 m for groundwater water level. The calibrated model was validated using measured data for October 2016, and root mean square error was found to be 0.81 m for groundwater water level. Among the observation wells which were used in the above analysis, 4 of them were directed to different aquifer depths and each two observation wells were in the same location. These two sets of wells, therefore, were used for analyzing interactions among different aquifer layers. Results showed that increased pumping rates enhanced water transfer between multilayers due to increased hydraulic gradient. The effect was more dominant in layers with high vertical hydraulic conductivity. Also, the sensitivity analysis was performed and results indicated that the predicted water level was less sensitive to vertical anisotropy. The findings of this study could be useful for decision-makers for better management of groundwater resources in arid regions.

ABSTRACT:

The growing population and increasing of the urbanization activities at the Egyptian coastal areas create a great demand on groundwater. El Negila which is located on the Northwestern coast of Egypt is of great environmental, economic, and social importance, so the sustainable management and preservation of the groundwater quantity and quality is imperative. Such task can be addressed through modeling tools that take into account both the human impacts and the effects of climate changes on the hydrogeological system. A variable-density flow model (SEAWAT) had been used to investigate the extent of the seawater intrusion the study area, and to introduce an effective management policy for sustainable development of the groundwater system. An attempt had been made for model calibration; based on adjusting the hydraulic head of the hydrogeological system with respect to the lineaments frequency in the study area. The calibrated numerical model showed the limited extent of the seawater intrusion in the study area under current recharge and abstraction conditions, in addition to that, the model was validated using hydrochemical and stable isotopic data. The aquifer response to different stressing pumping scenario has been tested and predicted up to the year 2022. Furthermore, the impact of rising the seawater level as a result of rapid climatic change was assessed, with pumping stress of the second scenario. It was concluded that the tableland area acts as recharge source and providing an opportunity of recharging the karstic aquifer in the study area especially through the lineaments. The extent of seawater intrusion in the study area for the karstic aquifer is limited, and would increase under the induced activities of pumping as well as seawater rise conditions. A range of withdrawal rate from the study area was recommended to avoid more invasions from seawater.

ABSTRACT:

The effects of human activities and sea-level changes on the spatial and temporal behaviour of the coupled mechanism of salt-water and freshwater flow through the Godavari Delta of India were analysed. The density driven salt-water intrusion process was simulated with the use of a SUTRA (Saturated-Unsaturated TRAnsport) model. Physical parameters, initial heads, and boundary conditions of the delta were defined on the basis of available field data, and an areal, steady-state groundwater model was constructed to calibrate the observed head values corresponding to the initial development phase of the aquifer. Initial and boundary conditions determined from the areal calibration were used to evaluate steady-state, hydraulic heads. Consequently, the initial position of the hydraulic head distribution was calibrated under steady-state conditions. The changes of initial hydraulic distribution, under discharge and recharge conditions, were calculated, and the present-day position of the interface was predicted. The present-day distribution of hydraulic head was estimated via a 20-year simulation. The results indicate that a considerable advance in seawater intrusion can be expected in the coastal aquifer if current rates of groundwater exploitation continue and an important part of the freshwater from the river is channelled from the reservoir for irrigation, industrial and domestic purposes.

ABSTRACT:

The Motooka area of Fukuoka prefecture of Japan is an agricultural area located on a coastal aquifer where the groundwater is being exploited for drinking and green house agriculture. The groundwater is the main water supply for drinking and greenhouse agriculture. With the increased water demand, groundwater is being extracted at the rate of 1,200m3/day. The salinity of the pumped water has been analyzed periodically and it has found that the aquifer is affected by the saltwater intrusion due to over exploitation of groundwater. The high salinity of pumped water is not suitable for both drinking and greenhouse farming. The salinity fluctuation in the pumped groundwater has become an important issue to attract much attention of the green house farmers due to its significant effect on their crops. To the authors' knowledge, research on the salinity fluctuations with groundwater pumping and their effects on seasonal recharge of groundwater in the Motooka region has not been conducted thus far. In the field of numerical modeling of saltwater intrusion, so far the simulation of salinity fluctuations is not significant. Therefore authors found a keen interest on numerical simulation of the saltwater intrusion and the salinity fluctuation phenomenon in the Motooka. To this end, a three dimensional density dependent finite difference solute transport numerical model was developed. Due to the distributed nature of pumping well locations and non-uniform geological conditions; a three-dimensional model was needed to understand the saltwater intrusion and salinity fluctuations in the Motooka. The developed model is capable of simulating the saltwater intrusion and the salinity fluctuations due to groundwater pumping for satisfactory extent.

ABSTRACT:

The effect of future climate scenarios on surface and groundwater resources was simulated using a modeling approach for an artificial recharge area in arid southern Iran. Future climate data for the periods of 2010-2030 and 2030-2050 were acquired from the Canadian Global Coupled Model (CGCM 3.1) for scenarios A1B, A2, and B1. These scenarios were adapted to the studied region using the delta-change method. A conceptual rainfall-runoff model (Qbox) was used to simulate runoff in a flash flood prone catchment. The model was calibrated and validated for the period 2002-2011 using daily discharge data. The projected climate variables were used to simulate future runoff. The rainfall-runoff model was then coupled to a calibrated groundwater flow and recharge model (MODFLOW) to simulate future recharge and groundwater hydraulic heads. As a result of the rainfall-runoff modeling, under the B1 scenario the number of floods is projected to slightly increase in the area. This in turn calls for proper management, as this is the only source of fresh water supply in the studied region. The results of the groundwater recharge modeling showed no significant difference between present and future recharge for all scenarios. Owing to that, four abstraction and recharge scenarios were assumed to simulate the groundwater level and recharge amount in the studied aquifer. The results showed that the abstraction scenarios have the most substantial effect on the groundwater level and the continuation of current pumping rate would lead to a groundwater decline by 18m up to 2050.

ABSTRACT:

The effect of future climate change on groundwater resources was assessed using a modelling approach for a coastal area in Vietnam. In this study, the distributed hydrological model (PANTA RHEI) was coupled with the finite element subsurface flow system model (FEFLOW) to predict the future variation of groundwater resources. The assessment of the seasonal variability of climate conditions on the variation of groundwater recharge and groundwater levels (GWLs) in different aquifers was analysed for the historical (1986-2005), present (2013-2014), and future (2046-2065) period. The domain groundwater model covers approximately 50 km(2). The groundwater model was calibrated and validated using hourly measured groundwater levels at 11 monitoring wells within the study area. The necessary information on geological formations, hydrogeological parameters, and groundwater abstraction rate were implemented in the groundwater model set up. One representative concentration pathway (RCP8.5) is considered for projecting future conditions of groundwater resources. The results of this study showed that future rainfall was projected to decrease both in wet and dry seasons. Groundwater recharge was projected to decrease significantly in the dry season (10.9%) compared to the wet season (2.6%). As a result, groundwater levels were also projected to decline in future. Stronger declining trends were detected for deeper groundwater, especially in the dry season with declines of 6.7-20.2 m. The model results also showed that the GWLs are largely influenced by the natural recharge through precipitation in the study area. These findings may help decision-makers and stakeholders for devising sustainable groundwater management strategies in coastal area.