Stephen Ferencz

UT Austin

Subject Areas: hydrology, water management, regulated rivers, surface water-groundwater interactions

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ABSTRACT:

This study combines detailed field observations and flow and heat transport modeling to assess the impact of hydropeaking on riverbed temperatures in a large regulated river. The field site was 12 km downstream from a dam that induces large daily flow variations. Vertical thermistor arrays were used to collect riverbed temperature data across the entire channel. The riverbed near the left bank was highly dynamic thermally, transitioning between river and groundwater temperatures over daily hydropeaking cycles. In contrast, the rest of the riverbed, including near the right bank, was similar in temperature to the river and had relatively stable temperatures. Modeling showed that the temperatures near the banks are explained by advective heat transport driven by hydrostatic changes in river level, while the temperatures over the rest of the channel can be explained mostly by conductive heating. Gaining groundwater conditions and high sediment hydraulic conductivity favor thermally dynamic zones near banks, while low hydraulic conductivity (below 1 m/d) and neutral or losing groundwater conditions result in muted temperature fluctuations, as observed at the right bank.

Here we provide:
1) The river temperature and stage data during the field study.
2) The vertical profile riverbed temperature data from the 21 profilers with data from 10, 20, 30, and 50 cm depth in the riverbed.
3) The survey data of the profiler locations.
4) A COMSOL model file that has the features used for the modeling study. The user can change the dimensions of the river to meet their own interests and also change the subsurface flow and heat transport prosperities.

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ABSTRACT:

Summary of the work that generated the associated data: Hydroelectric dams often create highly dynamic downstream flows that promote surface water-groundwater (SW-GW) interactions including bank storage, the temporary storage of river water in the riverbank. Previous research on SW-GW exchanges in dammed rivers have been local studies conducted within the bed or the bank, limiting the understanding of these exchanges which occur over potentially hundreds of kilometers. This study evaluates how dam releases affect SW-GW exchange continuously over a 100 km distance. This is accomplished by longitudinally routing water releases through a synthetic river and modeling bed and bank fluid and solute exchange across transverse transects spaced along the reach. Peak and square dam release hydrograph shapes with three magnitudes (0.5, 1.0, and 1.5 m) were considered. The effect of four ambient groundwater flow conditions (very slightly losing, neutral, and two gaining from the perspective of the river) were evaluated for each dam release scenario. Both types of dam release shapes cause SW-GW interaction over the entire 100 km distance, and our results show square type releases cause bank storage exchange well beyond this distance. Strongly gaining conditions reduce the amount of exchange and allow flushing of river-sourced solute out of the bank after the dam pulse has passed. Both neutral and losing conditions have larger fluid and solute flux into the bank and limit the amount of solute that returns to the river. Our results support that river corridors downstream of dams have increased river-aquifer connectivity, and that this enhanced connectivity can extend at least 100 km downstream.

This page has the following data:
-Copy of Comsol model that was used to generate bank storage exchange fluid flux and solute area (hyporheic zone size) results
-Data file of dam release boundary conditions used for the HEC-RAS routing model
-Time series of river hydrograph (depth) response at 1 km resolution. The data provided is for the results to the six dam release scenarios considered in this study exported from HEC-RAS models. Time is on x-axis and distance along river on y axis. The dam is located at river kilometer (rkm) 200 and descending distance indicates further downstream distance.
-All model output results from Comsol models - these include time series of both fluid flux rates across the river-channel boundary and the size of the hyporheic zone based on percentage of river water in the subsurface.

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ABSTRACT:

Summary of the work that generated the associated data: Hydroelectric dams often create highly dynamic downstream flows that promote surface water-groundwater (SW-GW) interactions including bank storage, the temporary storage of river water in the riverbank. Previous research on SW-GW exchanges in dammed rivers have been local studies conducted within the bed or the bank, limiting the understanding of these exchanges which occur over potentially hundreds of kilometers. This study evaluates how dam releases affect SW-GW exchange continuously over a 100 km distance. This is accomplished by longitudinally routing water releases through a synthetic river and modeling bed and bank fluid and solute exchange across transverse transects spaced along the reach. Peak and square dam release hydrograph shapes with three magnitudes (0.5, 1.0, and 1.5 m) were considered. The effect of four ambient groundwater flow conditions (very slightly losing, neutral, and two gaining from the perspective of the river) were evaluated for each dam release scenario. Both types of dam release shapes cause SW-GW interaction over the entire 100 km distance, and our results show square type releases cause bank storage exchange well beyond this distance. Strongly gaining conditions reduce the amount of exchange and allow flushing of river-sourced solute out of the bank after the dam pulse has passed. Both neutral and losing conditions have larger fluid and solute flux into the bank and limit the amount of solute that returns to the river. Our results support that river corridors downstream of dams have increased river-aquifer connectivity, and that this enhanced connectivity can extend at least 100 km downstream.

This page has the following data:
-Copy of Comsol model that was used to generate bank storage exchange fluid flux and solute area (hyporheic zone size) results
-Data file of dam release boundary conditions used for the HEC-RAS routing model
-Time series of river hydrograph (depth) response at 1 km resolution. The data provided is for the results to the six dam release scenarios considered in this study exported from HEC-RAS models. Time is on x-axis and distance along river on y axis. The dam is located at river kilometer (rkm) 200 and descending distance indicates further downstream distance.
-All model output results from Comsol models - these include time series of both fluid flux rates across the river-channel boundary and the size of the hyporheic zone based on percentage of river water in the subsurface.

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Ferencz_et_al_2021_bedheat_data_and_modeling
Created: Jan. 6, 2021, 8:23 p.m.
Authors: Ferencz, Stephen

ABSTRACT:

This study combines detailed field observations and flow and heat transport modeling to assess the impact of hydropeaking on riverbed temperatures in a large regulated river. The field site was 12 km downstream from a dam that induces large daily flow variations. Vertical thermistor arrays were used to collect riverbed temperature data across the entire channel. The riverbed near the left bank was highly dynamic thermally, transitioning between river and groundwater temperatures over daily hydropeaking cycles. In contrast, the rest of the riverbed, including near the right bank, was similar in temperature to the river and had relatively stable temperatures. Modeling showed that the temperatures near the banks are explained by advective heat transport driven by hydrostatic changes in river level, while the temperatures over the rest of the channel can be explained mostly by conductive heating. Gaining groundwater conditions and high sediment hydraulic conductivity favor thermally dynamic zones near banks, while low hydraulic conductivity (below 1 m/d) and neutral or losing groundwater conditions result in muted temperature fluctuations, as observed at the right bank.

Here we provide:
1) The river temperature and stage data during the field study.
2) The vertical profile riverbed temperature data from the 21 profilers with data from 10, 20, 30, and 50 cm depth in the riverbed.
3) The survey data of the profiler locations.
4) A COMSOL model file that has the features used for the modeling study. The user can change the dimensions of the river to meet their own interests and also change the subsurface flow and heat transport prosperities.

Show More