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Scope/Content: Abstract: Since the early 20th century, the Elwha River has been significantly altered by two hydroelectric dams which block passage of anadromous fish. In 1992, the U.S. Congress passed the Elwha River Ecosystem and Fisheries Restoration Act, requiring restoration of the ecosystem and the native salmon runs. Subsequent analysis determined that the dams would be removed, natural processes would redistribute the accumulated sediment, and restoration of native vegetation would be a central component of the project. Revegetating the reservoirs after dam removal is essential to ecosystem restoration. Draining the two reservoirs will expose almost 800 acres. Nearly 18 million cubic yards of sediment has accumulated in the reservoirs and much of it will be redistributed by the river as the dams are removed. The dewatered reservoirs will have few biological legacies valuable to restoration such as soil microbes, standing snags, or residual live plants. Soil nutrients and moisture availability will be low, and evaporation will be high due to intense sun and wind exposure. Much of the area will be far from intact forests which could provide seeds, spores, and detritus to speed succession. Thus, natural primary succession of the dewatered reservoirs would be slow. Populations of invasive exotic species may also influence the development of native vegetation. The goals for revegetating the reservoirs are to minimize invasive exotic species establishment, stabilize ecosystem processes and establish native forests. To achieve these goals, revegetation crews will actively revegetate most of the exposed areas, leaving areas close to native forests to regenerate naturally. The key strategy to prevent exotic species invasions is to control populations in the watershed before, during, and after dam removal to limit dispersal into the dewatered reservoirs. To further minimize invasive species, biologists and revegetation crews will install a diversity of native plant species over a period of seven years, employing multiple types of plant materials representing various life-stages (seeds, seedlings, and live-stakes). Installing plants into the dewatered reservoirs will also stabilize ecosystem processes. Seeding the valley walls with grasses and forbs will limit the erosion of fine sediments. Seeding the slopes will also hasten soil development. The primary objective of planting will be to initiate forest communities, particularly in central portions of the dewatered reservoirs far from surrounding, intact forests. Succession to mature forest will be accelerated by planting at variable densities and by installing dense patches of woody plants to facilitate plant survival and growth in the stressful conditions of the dewatered reservoirs. Scope/Content: Dam type: concrete Scope/Content: Dam type: gravity Scope/Content: Height: 108 feet. Scope/Content: Date constructed: 1913. Date removed: 2011.
Ecology and river restoration Pre- and post-project monitoring Dams Dam retirement