Most people tend to view dams as built to last forever but dams have a lifespan they fill with sediment, or they outlive their usefulness, or they’re removed for environmental reasons this is the case for Elwa Dam in Washington State. What is the Elwa Dam removal?
The Elwha Dam was built in 1914-Its removal began on September 17, 2011, & Six months later the Elwha Dam was gone-the biggest dam removal project ever leaving 83% restored 70 mi. of habitat on the Elwa River of the Elwha watershed permanently protected in Olympic National Park, Washington State USA.
The United States houses more than 90,000 dams, according to the National Inventory of Dams, most of which were built during a prolific construction boom in the early 1900s. Today, many of these dams are obsolete and no longer serve the purposes for which they were built.
Elwha Dam Removal
In 1992, Congress passed the Elwha River Ecosystem and Fisheries Restoration Act, authorizing dam removal to restore the altered ecosystem and the native anadromous fisheries therein. After two decades of planning, the largest dam removal in U.S. history began on September 17, 2011.
Removal of the Elwha Dam began in September 2011 and was complete by March 2012, allowing the Elwha River to flow freely through the area for nearly a century.
For over 100 years, the web of ecological and cultural connections in the Elwha Valley was broken then the river’s story changed the course of the river. In 1992, Congress passed the Elwha River Ecosystem and Fisheries Restoration Act, authorizing dam removal to restore the altered ecosystem and the native anadromous fisheries within the river.
After two decades of planning, the largest dam removal in U.S. history began on September 17, 2011. Six months later the Elwha Dam was gone, followed by the Glines Canyon Dam in 2014. Today, the Elwha River flows freely from its headwaters in the Olympic Mountains to the Strait of Juan de Fuca.
History of the Elwha Dam
In the early 1900s, two hydroelectric dams were built on the Elwha River in Washington State: the 32-m high Elwha Dam and the 64-m high Glines Canyon Dam. These dams blocked anadromous fish from accessing over 90% of the watershed for over a century. The dams also blocked the natural movement of sediment and wood to downstream habitats,
After decades of lobbying by the Lower Elwha Klallam Tribe and its allies, Congress passed the Elwha River Ecosystem and Restoration Act. Both dams were removed simultaneously over 3 years from 2011 to 2014 once again re-opening more than 70 miles of pristine salmon habitat. Dam removals of such magnitude had never been undertaken before.
American expansion helped spurred a continual demand for lumber. The growth of the logging industry in the region brought rapid change to the Olympic Peninsula and specifically to the Elwha River with the construction of two dams.
The Elwha and Glines Canyon river dams were built in the early 1900s, generating hydropower to supply electricity for the emerging town of Port Angeles and fueling regional growth on the Peninsula.
However, the construction of the dams blocked the migration of salmon moving upstream, disrupted the flow of sediment downstream, and flooded the historic homelands and cultural areas of the Lower Elwha Klallam Tribe.
The Lower Elwha Klallam Tribe is a sovereign, federally-recognized Indian Nation, with its own constitution and government. Not only does the Tribe govern itself, but many Tribal administrative departments oversee the everyday function of the reservation and provide for Tribal members.
The Lower Elwha Klallam Tribe resides in the Lower Elwha River Valley and adjacent bluffs on the north coast of the Olympic Peninsula west of Port Angeles, Washington. As recognized by the United States in the 1855 Treaty of Point No Point, the Lower Elwha Klallam Tribe has lived in this area since time immemorial. Today tribal lands include about a thousand acres of land on and near the Elwha River.
Elwha Ecosystem Restoration Project
The Elwha Ecosystem Restoration Project is a 21st-century project of the U.S. National Park Service to remove two dams on the Elwha River on the Olympic Peninsula in Washington State and restore the ecosystem of the river to a pure natural state.
The Elwha Dam removal has resulted in the release of millions of cubic yards of sand and silt to the nearshore waters of the Strait of Juan de Fuca. The damming of the Elwha River dramatically reduced sediment flow to the coast leading to rapid erosion of the shoreline of the Elwha River delta. The removal of the dams has resulted in the release of millions of cubic yards of sand and silt to the nearshore waters of the Strait of Juan de Fuca.The Northwest Fisheries Science Center’s Elwha River Restoration Project gives a unique opportunity to study ecosystem restoration at a watershed scale. Researchers in their Watershed Program work with the Lower Elwha Klallam Tribe and other partners such as Olympic National Park to study this historic undertaking’s ecological importance.
Together, they are examining how riverine, estuarine, and nearshore habitats are changing due to dam removal, and what this means to the entire Elwha River ecosystem.
And so one of the really great results that removing the dam did is it actually restored the delta where the River meets the Strait of Juan de Fuca and rebuilt this entire beach and lagoon area that had gotten deprived of all of this sediment. So seeing all that soil moved downstream was part of the natural process.
River Salmon Dam Removal
Dam removal restores a river’s natural flow and helps increase biodiversity because vegetation and habitats are restored. Wetlands are revitalized, creating alcoves that serve as nurseries for native aquatic species, and enhancing plant growth along riverbanks that provide habitat and food for additional wildlife species.
Dam removal replaces warmer water species with native species that are adapted to colder water such as salmon, trout, shad, river herring, etc., and enables native fish to migrate freely upstream and downstream, improving their chances for successful reproduction.
Different techniques will be used to remove the two dams. At the Elwha Dam, which is broad and relatively short, the reservoir water level will first be lowered through existing spillways.
Cofferdams, temporary enclosures, will be built to divert water into separate channels so that the river’s original channel can be excavated. After the powerhouse and other structures are removed, the diversion channel will be filled in and the river will be returned to its natural flow path.
The dismantling of the taller Glines Canyon Dam will involve the construction of temporary spillways on either side of the dam to drain the reservoir, then layers of the river dam will be removed as the water level lessons. Finally, what’s left will be blasted away to restore the river’s natural flow.
There are several ways river dams can be removed and the chosen method will depend on many factors. The size and type of the dam, the amount of sediment held behind the dam, the aquatic environment below the ecosystem below the dam, who owns the dam what their priorities are, and the timeframe of dam removal are all important factors that affect how the dam will be removed.
The Result of the Elwha Dam Removal
Removal is expensive no matter what and costs typically rise when greater weight is given to environmental concerns. Fortunately, the cost of river dam removal is usually shared by multiple stakeholders such as the dam owner and either the federal, state, or local government.
The dam removal process will take 2 ½ to 3 years because 15 million cubic yards of sediment have been collected behind the dams; the release of this sediment must be carefully controlled to protect a downstream fish hatchery, the Lower Elwha reservation, and the Port Angeles drinking water supply. Once the nutrient-rich sediment flows downstream, however, it will help restore the estuary, salmon habitats, and beaches and bring them back to normal.
The return of the river salmon, which will convey nutrients from the ocean and be a source of food when they die, will also support many other wildlife and aquatic species. The area will be replanted to prevent erosion and restore native ecosystems. The Lower Elwha Klallam tribe will finally have their sacred sites and the salmon, the basis of their culture, restored to where it once was.
River Dams have been built to provide recreation, flood control, fire protection, irrigation, water supplies, or hydroelectric power. Most were built for recreation and flood control and only 2,210 generate hydropower.
Today, however, many U.S. dams have outlived their original purpose and over 4,000 have been deemed unsafe. By 2020, 85% of U.S. dams will be over 50 years old, which is typically the average life of a U.S. river dam.
Often a dam is removed in order to undo the multiple detrimental impacts it has on the environment and biodiversity. Dams divert water from rivers for power, reducing the supply of water available to keep downstream ecosystems healthy.
River Dams obstruct the migration of fish, endangered species, and other wildlife; for example, the U.S. Fish and Wildlife Service estimates that 91% of the migratory fish like salmon habitat in northern New England is blocked by dams.
Dams also prevent nutrient-rich sediments and woody debris needed for habitats from flowing downstream. Dams slow the flow of rivers, which allows sediment to collect on the river bottom and bury the spawning habitat.
The slowed flow also disorients fish species whose lifecycles evolved to take advantage of the swiftness and natural seasonal variations of a river’s flow. The warmer temperature of reservoir water sitting behind a dam may discourage cool-water fish species from reaching their upstream spawning locations.
Water that is released from the bottom of the reservoir is much colder and contains less oxygen than river water, which can affect the reproductive processes of some fish species; and when water with depleted oxygen can kill downstream fish. In addition, the creation of reservoir lakes favors species better suited to lake-like conditions, which often harm native fish species.
The river sediment and silt trapped by dams can accumulate heavy metals and pollutants. And turbines at hydropower dams may injure fish.
Dam removal may, however, stir up sediments as they are carried down a free-flowing river and this resuspension can damage spawning grounds and habitat, and affect H2O quality, especially if the sediments involve toxins and pollutants.
When the Fort Edward Dam on New York’s Hudson River was removed in 1973, sediments behind the dam had not been tested. As a result, tons of sediment-laden with toxic PCBs that had been dumped by General Electric (GE) were washed downstream, affecting human and wildlife health.
GE is now in the process of dredging the polluted sediments. But in most cases, resuspension problems are temporary. Silt and sediment from the Grangeville and Lewiston Dams on Idaho’s Clearwater River washed downstream in a week after the dam removals in 1963 and 1973 respectively; sediment from the Milwaukee River in Wisconsin settled six months after the Woolen Mills Dam was removed in 2007.
There are known strategies to minimize resuspension problems: timing the release of sediments to avoid spring runoff, slowly drawing down the reservoir first, trapping sediment in screens, and dredging the sediments in the reservoir.
Conclusion:
Dam removal is an important tool for river restoration and addressing aging infrastructure. It is an ongoing activity that will continue as a large number of aging dams that are no longer serving their original purposes, have become safety liabilities, or represent potential for significant restoration action are taken down. The increase in the number of dams removed has led to a greater understanding of the outcomes for the river and its ecosystem. Since 2000 the number of dams removed has been greater each year than the number of dams constructed.
References:
The Lower Elwha Klallam Tribe- Culture and History
National Park Service- Elwha Restoration
