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Laboratory Flume and Numerical Modeling Experiments Show Log Jams and Branching Channels Increase Hyporheic Exchange
Author(s) -
Wilhelmsen K.,
Sawyer A. H.,
Marshall A.,
McFadden S.,
Singha K.,
Wohl E.
Publication year - 2021
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 - 10.1029/2021wr030299
Subject(s) - flume , jams , streams , hydrology (agriculture) , hyporheic zone , channel (broadcasting) , environmental science , flow (mathematics) , groundwater , geology , geometry , mathematics , geotechnical engineering , chemistry , engineering , computer science , computer network , food science , electrical engineering
Log jams alter gradients in hydraulic head, increase the area available for hyporheic exchange by creating backwater areas, and lead to the formation of multiple channel branches and bars that drive additional exchange. Here, we numerically simulated stream‐groundwater interactions for two constructed flume systems—one without jams and one with a series of three jams—to quantify the effects of interacting jam structures and channel branches on hyporheic exchange at three stream flow rates. In simulations without jams, average hyporheic exchange rates ranged from 2.1 × 10 −4 to 2.9 × 10 −4 m/s for various stream discharge scenarios, but with jams, exchange rates increased to a range of 1.3 × 10 −3 –3.5 × 10 −3 m/s. Largely due to these increased hyporheic exchange rates, jams increased stream‐groundwater connectivity or decreased the turnover length that stream water travels before interacting with the hyporheic zone, by an order of magnitude, and drove long flow paths that connected multiple jams and channel threads. Decreased turnover lengths corresponded with greater reaction significance per km, a measure of the potential for the hyporheic zone to influence stream water chemistry. For low‐flow conditions, log jams increased reaction significance per km five‐fold, from 0.07 to 0.35. Jams with larger volumes led to longer hyporheic residence times and path lengths that exhibited multiple scales of exchange. Additionally, the longest flow paths connecting multiple jams occurred in the reach with multiple channel branches. These findings suggest that large gains in hydrologic connectivity can be achieved by promoting in‐stream wood accumulation and the natural formation of both jams and branching channels.