Analysis of the effects of dam release properties and ambient groundwater flow on surface water‐groundwater exchange over a 100 km‐long reach

Stephen B. Ferencz, M. Bayani Cardenas, Bethany T. Neilson
2019 Water Resources Research  
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.
more » ... s 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. Plain Language Summary Rivers downstream from dams that generate hydroelectric power can experience frequent water level changes as discharge from the dam is increased or decreased to meet electricity demands. Dam releases can be of similar size to storm runoff events caused by precipitation, but they often occur with more regularity. A large body of research indicates that the exchange of surface water and groundwater (SW-GW) can play an important role in the ecology, nutrient cycling, and overall ecosystem health of river environments. This study uses computer simulations to evaluate how dam releases affect SW-GW interactions. Instead of collecting observations at a handful of field locations as typically done, our approach enabled us to test how a wide range of dam release properties affect SW-GW interactions continuously over a long distance downstream. Our results show that depending on the type and size of hydropower release and the groundwater conditions, the volume of exchange between the river and groundwater can range from 1 to almost 200 Olympic swimming pools over a 100 km length of river. Our findings can help predict where hydropower operations are more likely to cause SW-GW exchange and thus help management of river corridors and guide future studies in dammed rivers.
doi:10.1029/2019wr025210 fatcat:l7brhd4trfdt3i62kjcxnk25fa