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WATER QUALITY RAMIFICATIONS OF TEMPORARY DRAINAGE OF OREGON RESERVOIRS TO FACILITATE JUVENILE CHINOOK SALMON PASSAGE

Reservoirs can support anadromous salmonids but the dams may impede fish passage downstream. The Willamette River system in Oregon (USA) has a number of such dams, including the Fall Creek Reservoir. Managers are experimenting with deep drawdowns of that reservoir to promote downstream passage of juvenile endangered Chinook Salmon, and to discourage invasive fish species that prey on or compete with the salmon. Over the past four years we have studied the downstream water quality changes during these drawdowns, which reach stream bed in the late autumn. We found modest increases in available nutrient concentrations due to drainage of near-bottom water and surficial sediment porewaters, but the increase is ephemeral and unlikely to cause eutrophication. Upon reaching stream bed there is much erosion and export of fine sediments. The oxygen demand of these sediments is not high. Sedimentation of downstream habitats is the greatest concern, but careful management of the drawdown could mitigate sediment export.

Stephen Hamilton (Primary Presenter/Author), Michigan State University, hamiltonsteve811@gmail.com;


Christina Murphy ( Co-Presenter/Co-Author), Oregon State University, Department of Fisheries & Wildlife, christina.murphy@oregonstate.edu;


Sherri Johnson ( Co-Presenter/Co-Author), U.S. Forest Service, Pacific Northwest Research Station, sherrijohnson@fs.fed.us;


Ivan Arismendi ( Co-Presenter/Co-Author), Oregon State University, Department of Fisheries & Wildlife, ivan.arismendi@oregonstate.edu;