Ecological Process WED hydrologists studying the Willamette River in western Oregon have documented a significant subsurface flow through gravel deposits. Such a filtering process is an important ecological mechanism for a river. The scientists used fluorescent dye tracers and precise measurements of flow to track the movement of river water through gravel deposits along a 26-kilometer stretch of the Willamette River through agricultural lands between Eugene and Corvallis. From their analysis, they estimated that more than 70 percent of the river s flow at some point becomes hyporheic, that is, it leaves the channel to flow through subsurface gravels and other deposits. The study found that the most hyporheic flow occurs where the river is free to move, creating extensive, highly porous gravel deposits, and where the channel is not constrained by revetment structures that harden its banks.
Hyporheic flow has beneficial effects on water quality and aquatic habitat.
It affects the river s water both physically, for example by cooling it, and biochemically, for example by reducing the amount of dissolved nitrogen. Results of the study suggest that river management aimed at ecological enhancement should focus on decreasing channel constraints and restoring natural hydrogeomorphic processes.