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TRANSIENT STORAGE AND HYPORHEIC FLOW ALONG THE UPPER WILLAMETTE RIVER, OREGON: FIELD MEASUREMENTS AND MODEL ESTIMATES
Citation:
Fernald, A. G., P. J. WIGINGTON JR, AND D H. Landers. TRANSIENT STORAGE AND HYPORHEIC FLOW ALONG THE UPPER WILLAMETTE RIVER, OREGON: FIELD MEASUREMENTS AND MODEL ESTIMATES. WATER RESOURCES RESEARCH. American Geophysical Union, Washington, DC, 37(6):1681-1694, (2001).
Description:
Transient storage measures the exchange of main channel flow with subsurface hyporheic flow and surface water dead zones. Hyporheic flow, in which river water enters the channel bed and banks to emerge downstream, promotes biochemical processes that are iimportant for water quality and aquatic habitat. Previous studies have quantified transient storage and hyporheic flow on small streams but have not been specifically developed to identify transient storage and hyporheic flow over long reaches of large rivers. We studied transient storage on the ninth-order Upper Willamette River, which flows through high porosity gravel deposits conducive to hyporheic flow. We used main channel dye tracer studies and solute transport modeling to estimate transient storage on nine study reaches in a 26 km-long study area. We also took dye measurements from the transient storage zone itself to identify transient storage flow paths. With main channel dye tracers and simulation modeling we obtained estimates of transient storage exchange coefficient and transient storage to mail channel cross-sectional area. These transient storage values show that significant amounts of water followed transient storage flow paths which had 0,2 to 30 hour residence times. Our dye measurements from the transient storage zone itself showed that both subsurface and surface flow paths were important components of transient storage. Channel discharge gains and losses suggest that on the order of 70% of Willamette River water may move through hyporheic flow paths over the 26 km study reach. Much of the historical natural channel complexity that normally promotes hyporheic flow no longer exists on the Upper Willamette River. Our results suggest that river management targeted to increase transient storage and the ecological enhancement provided by hyporheic