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GroMoPo Metadata for New Zealand national model


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Created: Feb 06, 2023 at 8:55 p.m.
Last updated: Feb 06, 2023 at 8:56 p.m.
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Abstract

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.

Subject Keywords

Coverage

Spatial

Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
Place/Area Name:
New Zealand
North Latitude
-34.9000°
East Longitude
178.5000°
South Latitude
-47.4000°
West Longitude
166.4000°

Content

Additional Metadata

Name Value
DOI 10.5194/hess-22-6449-2018
Depth 500
Scale National
Layers 1 layer
Purpose groundwater resources;scientific investigation
GroMoPo_ID 20
IsVerified True
Model Code Equilibrium Water Table approach, coded in Python and Matlab
Model Link https://doi.org/10.5194/hess-22-6449-2018
Model Time SS (mean of 2000 - 2015 recharge used)
Model Year 2018
Model Authors R. Westerhoff
Model Country New Zealand
Data Available output publicly available;https://rogierwesterhoff.users.earthengine.app/view/nzwatertable
Developer Email r.westerhoff@gns.cri.nz
Dominant Geology Model focuses on multiple geologic materials
Developer Country New Zealand
Publication Title Application of an improved global-scale groundwater model for water table estimation across New Zealand
Original Developer Yes
Additional Information This dataset is a model-derived steady-state mean water table at the New Zealand nationwide scale with a resolution of 250m x 250m. These data are described in Westerhoff et al. (2018) – URL: https://hess.copernicus.org/articles/22/6449/2018/ . The model used aimed for 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. The model is inspired by an existing, global-scale, groundwater flow model and improved 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.
Integration or Coupling Surface water
Evaluation or Calibration static water levels
Geologic Data Availability

How to Cite

GroMoPo, R. Westerhoff (2023). GroMoPo Metadata for New Zealand national model, HydroShare, http://www.hydroshare.org/resource/496f1c7a36a241d18c3182237d0e1513

This resource is shared under the Creative Commons Attribution CC BY.

http://creativecommons.org/licenses/by/4.0/
CC-BY

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