The Sediments of the Elwha River: A Preliminary Study of the Affects of Dam Removal

Project ID: J9W88050005

Federal Agency: National Park Service

Partner Institution: University of Washington

Fiscal Year: 2005

Initial Funding: $14,995

Total Funding: $14,995

Project Type: Research

Project Disciplines: Physical

National Park: Olympic National Park

Principal Investigator: Zabowski, Darlene

Agreement Technical Representative: Acker, Steven

Abstract: The Elwha and the Glines Canyon Dams of the Elwha River in Olympic National Park are scheduled to be removed in 2008. The dams currently block anadromous fish passage to most of the 70 miles of the Elwha River, limiting those fish to less than five miles of the lower river. Removal of the two dams has been proposed to restore endangered anadromous salmon to the Elwha River. However, dam removal affects not only aquatic biota, but also the riparian habitats associated with river margins and floodplains. If the sediment is not stabilized, excessive amounts could erode downstream causing turbid waters and health threats to salmon. When the dams are removed, it is estimated that half of the reservoir sediment will erode downstream and the remaining sediment remain in situ. Concerns regarding the remaining sediments include infestation with invasive plants, wind and water erosion, and cracking. This project will address these concerns by conducting experiments on the sediment to predict erosivity and prescribe mulches or amendments that could prevent erosion and reduce establishment of invasive species. In addition, soil and vegetation ecosystem development on glacial lake sediments in the Elwha area will be examined to predict long-term soil development and ecosystem succession. As an additional aspect of describing baseline conditions prior to dam removal, areas around the two reservoirs will sampled to quantify 15N levels.