Sediment management strategies associated with dam removal in the State of Washington

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Abstract

Different removal strategies are described for dams in three diverse drainage basins (Wind River, White Salmon River, and Elwha River basins) in the State of Washington (USA). The comparisons between the strategies offer the opportunity to track the effects of sediment resulting from dam decommissioning in the Pacific Northwest and to determine possible effects on socio-economically important species of anadromous salmonids. Hemlock Dam, located on Trout Creek and managed by the United States Forest Service, was removed from July to September 2009. To mitigate the effect on fish downstream (specifically, salmonids) and to minimize sediment aggradation downstream in the main-stem Wind River, the Forest Service chose to excavate the approximately 42,000 cubic meters of sediment entrapped behind the dam before removal of the dam. Thus, the reach of Trout Creek downstream of the dam will not be affected by a large, released pulse of accumulated sediment. In contrast, the scheduled removal of Condit Dam, located on the White Salmon River 30 kilometers to the east of Hemlock Dam, involves a different removal strategy. Condit Dam will be breached near its base in order to mobilize the 1.7 million cubic meters of trapped sediment during the reservoir drawdown in an effort to decrease the time needed for the downstream reach to return to normal levels of suspended sediment. Finally, the much-anticipated 2011 removal of two dams on the Elwha River on the Olympic Peninsula in northwestern Washington will take place over 2 years with progressive notches cut into the dams from the top down. Although some portion of reservoir sediment will be carried downstream by the river, the specific timing of notching will be adaptively managed to mitigate the effects of raised sediment concentration on fishes and people living downstream. With improved scientific understanding from these studies, future damremoval projects can be planned and executed with approaches that mitigate deleterious effectson salmonids.

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Sediment management strategies associated with dam removal in the State of Washington
Year Published 2010
Language English
Contributing office(s) Western Fisheries Research Center, Pacific Coastal and Marine Science Center, Washington Water Science Center
Description 10 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Proceedings of the 2nd Joint Federal Interagency Conference (9th Federal Interagency Sedimentation Conference and 4th Federal Interagency Hydrologic Modeling Conference)
Conference Title 2nd Joint Federal Interagency Conference
Conference Location Las Vegas, NV
Conference Date June 27 - July 1, 2010
Country United States
State Washington
Other Geospatial Condit Dam, Glines Canyon Dam, Elwha Dam, Hemlock Dam