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Water Resources Research




Wiley-Blackwell Publishing, Inc.

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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 has primarily been at single study sites, which has limited the understanding of how these exchanges evolve as dam releases travel downstream. 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) was 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 that 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.