Changes in Streambed Composition in Salmonid Spawning Habitat of the Elwha River during Dam Removal |
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| Authors: | Roger J Peters Martin Liermann Michael L McHenry Paul Bakke George R Pess |
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| Affiliation: | 1. Western Washington Fish and Wildlife Conservation Office, U.S. Fish and Wildlife Service, Lacey, Washington;2. Northwest Fisheries Science Center, NOAA Fisheries, Seattle, Washington;3. Natural Resources Department, Lower Elwha Klallam Tribe, Port Angeles, Washington |
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| Abstract: | One uncertainty associated with large dam removal is the level of downstream sediment deposition and associated short‐term biological effects, particularly on salmonid spawning habitat. Recent studies report downstream sediment deposition following dam removal is influenced by proximity to the source and river transport capacity. The impacts of dam removal sediment releases are difficult to generalize due to the relatively small number of dam removals completed, the variation in release strategies, and the physical nature of systems. Changes to sediment deposition and associated streambed composition in the Elwha River, Washington State, were monitored prior to (2010‐2011) and during (2012‐2014) the simultaneous removal of two large dams (32 and 64 m). Changes in the surface layer substrate composition during dam removal varied by year and channel type. Riffles in floodplain channels downstream of the dams fined and remained sand dominated throughout the study period, and exceeded levels known to be detrimental to incubating salmonids. Mainstem riffles tended to fine to gravel, but appear to be trending toward cobble after the majority of the sediment was released and transported through system. Thus, salmonid spawning habitats in the mainstem appear to have been minimally impacted while those in floodplain channels appear to have been severely impacted during dam removal. |
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| Keywords: | sediment sediment transport sediment composition restoration environmental impacts |
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