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Studying the Elwha River, Washington, in Preparation for Dam Removal
In a few years, the Federal Government will begin the biggest dam removal in U.S. history, restoring a major coastal watershed and its prized salmon river on the Olympic Peninsula, Wash. U.S. Geological Survey (USGS) scientists are already working on the Elwha River Restoration Project, which has been in the works for many years, being planned by organizations that include the National Park Service (NPS), the Bureau of Reclamation, and the Lower Elwha Klallam Tribe. The project will involve removing two large dams on the Elwha River to help restore this stream and the associated coastal zone to a more natural state and to improve ecosystem health (see related Sound Waves article, "Dam Removal on the Elwha River in Washington—Nearshore Impacts of Released Sediment"). Elwha and Glines Canyon Dams were completed on the Elwha River in 1913 and 1927 at heights of 32 and 64 m, respectively, to provide hydropower for local timber companies. The dams blocked the natural supply of sediment to the lower river and coast, causing changes on the flood plain and erosion of beaches downdrift (east) of the river mouth. Because the dams were built without fish passage, their presence has greatly limited the available spawning run for salmon and steelhead, fish that spend most of their lives in the ocean but return to the stream where they hatched in order to reproduce. These native fish populations have declined severely in the Elwha watershed and around the Pacific Northwest, owing partly to the dam-related loss of their river spawning habitat. At present, salmon and steelhead have only 7.8 km of the river to use as spawning habitat (the distance from the river mouth to Elwha Dam). After dam removal, more than 70 km of the river should eventually become usable habitat for these fish. In 2000, the Federal Government purchased Elwha and Glines Canyon Dams from the timber companies that formerly owned them. It was agreed that because both dams were aging and needed costly repairs, a better alternative to repairing them would be to remove them and thereby restore the river habitat. Dam removal will take place in stages over 2 years and is scheduled to begin in 2009. This will be the first watershed-restoration project in which dams this large will be removed, and so it presents a unique opportunity to study how a river and coastal system respond to the changes that will follow dam removal, especially the reintroduction of sediment as the river erodes much of the sediment now trapped in the two reservoirs. More than 80 percent of the Elwha watershed lies within the boundary of Olympic National Park and has never been developed. It is hoped that dam removal will improve not only the native fish populations but also the general condition of the ecosystem in this largely pristine area. Scientists from the USGS Western Coastal and Marine Geology (WCMG) team are part of a large, interdisciplinary group of researchers studying the Elwha watershed as agencies gear up for dam removal. In September 2006, Amy Draut, Tom Reiss, and Josh Logan conducted the first of numerous planned USGS surveys of the river channel. They documented channel topography and sediment grain size in three study areas between Elwha Dam and the river mouth. They also surveyed part of the river channel upstream of both dams, at a site in Olympic National Park, to use as a "control" area to monitor changes in channel form and sediment unrelated to the dams or dam removal. These four sites will be revisited twice a year, in spring and fall, to document the magnitude of changes that occur seasonally in the dammed system. After dam removal begins, the scientists will continue to monitor these areas to evaluate how the river and intertidal zone change when the reservoir sediment begins to move downstream. In addition to the research in the river channel and intertidal zone, WCMG scientists Guy Gelfenbaum, Guy Cochrane, Jon Warrick, and Dave Rubin are leading mapping and oceanographic profiling in the nearshore zone and farther offshore along the coast. USGS specialists in biology, hydrology, and geography are also conducting studies related to dam removal. USGS scientists are working closely with the Lower Elwha Klallam Tribe, the National Oceanic and Atmospheric Administration (NOAA), and the NPS to learn as much as they can from this first-of-its-kind comprehensive watershed-restoration experiment. For more information, visit Elwha River Restoration and Elwha River Restoration Project or contact Amy Draut at adraut@usgs.gov or 831-427-4733.
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in this issue:
Effects of Urbanization on Nearshore Ecosystems in Puget Sound Studying the Elwha River in Preparation for Dam Removal Sea-Floor Mapping Project Expands to South Shore and Cape Cod Bay
Google Maps View of Western Coastal and Marine Geology Projects Benthic Sponge Taxonomy Course at Mote Marine Laboratory
Nov. / Dec. 2006 Publications List |
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U. S. Department of the Interior | U.S. Geological Survey
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