Premium
In‐stream geomorphic structures as drivers of hyporheic exchange
Author(s) -
Hester Erich T.,
Doyle Martin W.
Publication year - 2008
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2006wr005810
Subject(s) - modflow , hydrogeology , hyporheic zone , hydrology (agriculture) , streams , downwelling , equifinality , hydraulic conductivity , stream restoration , geology , hydraulics , groundwater , environmental science , sediment transport , urban stream , groundwater flow , sediment , geomorphology , soil science , aquifer , geotechnical engineering , ecology , engineering , computer network , oceanography , aerospace engineering , upwelling , computer science , soil water , biology
Common in‐stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams. Exchange is important for ecological stream function, and restoring function is a goal of many stream restoration projects, yet the connection between in‐stream geomorphic form, hydrogeologic setting, and hyporheic exchange remains inadequately characterized. We used the models HEC‐RAS, MODFLOW, and MODPATH to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in‐stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange. We also conducted a field study to support model results. Model results indicated that structure size, background groundwater discharge rate, and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange, followed by geomorphic structure type, depth to bedrock, and channel slope. Model results indicated channel‐spanning structures were more effective at driving hyporheic flow than were partially spanning structures, and weirs were more effective than were steps. Across most structure types, downwelling flux rate increased linearly with structure size, yet hyporheic residence time exhibited nonlinear behavior, increasing quickly with size at low structure sizes and declining thereafter. Important trends in model results were observed at the field site and also interpreted using simple hydraulic theory, thereby supporting the modeling approach and clarifying underlying processes.