The nation's largest dam removal project began in Sept 2011 on the Elwha River, located on the Olympic Peninsula in Washington State. The 108 feet (33m) high Elwha Dam and the 210 feet (64 m) Glines Canyon Dams were dismantled, re-opening more than 70 miles of pristine salmon habitat in the Olympic National Park that has been blocked to anadromous fish passage for over a century.
NOAA has been continuously gathering information to understand the impacts that the removal of these dams will have on the Elwha River, the salmon populations, and local, regional, and national communities. In conjunction with its partners, NOAA is conducting long-term monitoring in the lower Elwha River to establish baseline habitat conditions, fish presence and quantity, and habitat use and distribution and plans to continue the effort during and post-dam removal.
A dam removal of such magnitude has never been undertaken. Monitoring the changes to the river, the estuary, and the nearshore habitat, as well as the impacts of these changes to society is critical to tell the story of what happens after the dams are gone. How will the fish use the newly opened habitat? How will the ecosystem recover and how quickly? How will the changes impact communities? Without the complete story of the Elwha after the dams are gone, we will miss an opportunity to better understand our river systems, manage our fisheries, and inform future dam removals.
As a result of the presence of these dams, what was once one of the most productive salmon rivers on the Olympic Peninsula has been reduced to a fraction of its former productivity. In addition to blocking fish passage, the dams have trapped an immense quantity of sediment behind the dams, greater than 19 million cubic yards or enough to fill the Louisiana Superdome nearly five times. The removal of the dams is predicted to allow natural processes to resume, nourishing the lower river, estuary, and nearshore environment through the transport of sediment, large woody debris, and nutrients from the upper watershed.
While the dams were the major impact on the Elwha River, the health of the lower floodplain has been significantly degraded by human activities. The Lower Elwha Klallam Tribe, in partnership with NOAA, is restoring habitat forming processes in the lower river to speed the recovery of the river and create refuge habitat for salmon to access during the dam removal. These actions include removing abandoned push up dikes and constructing engineered logjams that will allow the river to form side channels and reconnect to its floodplain. The Tribe is also reforesting the lower floodplain by planting native species and eradicating exotic plants. Additional actions have been identified in the middle and lower portions of the river as well as in the estuary and nearshore habitat that will further speed complete watershed recovery.
Read the related feature story, "Restoring the Elwha River."
Download the Elwha River Dams Removals fact sheet.
Explore NWFSC's Watershed Program.
Learn more about our Lower Elwha restoration work and other coastal recovery projects in your state.