After the 1992 Elwha River Ecosystem and Fisheries Restoration Act was passed, a number of alternatives for restoration were explored by the Department of the Interior. The Final Programmatic EIS (
environmental impact statement), released in June 1995, concluded that the only way to fully restore the river was to remove both dams. The Final Implementation EIS, released in November 1996, concluded that sediment that had accumulated in the two reservoirs should be allowed to erode and disperse naturally downstream. Removal of the Elwha Dam began in September 2011 and was finished in spring 2012, ahead of schedule. Removal of the second dam, the
Glines Canyon Dam, was completed on August 26, 2014. The dam removal process was originally projected to last two and a half to three years. The estimated cost of removing both dams was $40 to $60 million. The total cost of the Elwha River restoration is approximately $351.4 million. This price includes the purchase of the two dams and related facilities, construction of two water treatment plants and other facilities to protect water users, and construction of flood protection facilities, a fish hatchery, and a greenhouse for growing native plants for
revegetation. After the removal of the dams, 10.5 million metric tons of sediment was released from two reservoirs through the Elwha river system. The sudden increase of sediment supply caused bed
aggradation of ~1 meter, resulting in a change of
channel morphology from pool-riffle to braided, and decreased the slope of the lowermost river. Widespread bed aggradation forced flow through floodplain channels, depositing additional sediment in the side channels of the Elwha river floodplain. Mainstream aggradation also formed numerous bars, further establishing braided morphology. The river system showed a greater geomorphic response to dam removal than it had to a 40-year flood event four years before dam removal. The dams had virtually eliminated bed-material sediment supply to the river downstream, forming large deltas upstream of each reservoir. Once released, the sediment travelled downstream to the mouth of the river, where a new estuary is believed to be forming. These geomorphic alterations have important ecological implications, affecting aquatic habitat structure,
benthic fauna, salmonid spawning and rearing potential, and
riparian vegetation. The process of
hydrochory after dam removal has increased the distribution of seeds downstream, allowing for the dispersal of seeds that were previously blocked off. This has restored hydrochory on the river and the return of riparian vegetation downstream. Actively restored sites and recolonized sites have not developed significant populations of invasive species. The response of the Elwha River system to the dam removals provides a unique and important case study for future river restoration projects.
Salmon Restoration The restoration of anadromous and migratory fish populations connectivity and habitat are primary goals of the restoration project. Anadromous and migratory fishes previously lost 90% of their habitat due to the dams. After dam removal, eight anadromous species swiftly ascended upstream into areas previously impeded, restoring connectivity, permitting the return of fish upstream and increasing their spatial distribution and density. ==Partnerships, research, and education==