Pulling the plug: Annually draining a reservoir to help salmon

Dams and the reservoirs they create are notorious for disrupting the migration of salmon, both when they travel downstream as juveniles and when they return to spawn years later as adults.

In an effort to improve downstream salmon migration, the U.S. Army Corps of Engineers in 2011 began yearly, short-term draining of Fall Creek Reservoir located on a tributary of the Willamette River in Oregon. The reservoir is drained down to the streambed over one week every autumn. The full effects of this novel practice were largely unknown until researchers Sherri Johnson and Christina Murphy launched an in-depth study.
 

Annual draining did not negatively impact water quality or food availability for juvenile salmon who entered reservoirs the following spring. Draining caused predatory fish to shift their diets away from salmon fry and reduced invasive fish to a point where, today, virtually none remain in the reservoir.

It’s not clear if reservoir draining alone will lead to more returning adult salmon, but the researchers are confident that it is a net benefit for downstream migration, a necessary step in the salmon lifecycle.

This research is being used to evaluate future dam management scenarios, including improving fish passage downstream, changing water levels associated with climate change and drought, and drawdowns for maintenance.

Citation

Kirkland, John; Johnson, Sherri; Murphy, Christina A. 2021. Pulling the plug: Annually draining a reservoir to help salmon. Science Findings 244. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.

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