Elwha Watershed Information Resource

The removal of the Elwha and Glines Canyon Dams is scheduled to begin in 2012. The removal project is expected to take two years to complete; however, efforts to restore the Elwha River watershed to its pre dam condition will take much longer. The scale of these dam removals and the subsequent watershed restoration make it one of the largest efforts of its kind in U.S. history.

The sections below provide a brief overview of the removal strategy and a discussion of what to expect during the transition period after the dams are removed. For more detailed information, review the Environmental Impact Statements that thoroughly describe the plans to:

• Deconstruct the dams,
• Maintain water supplies downstream,
• Manage the sediments of the river, and
• Restore the ecological function of the entire watershed.

Dam Removal

Glines Canyon Dam. Mark Hollingsworth, Bureau of Reclamation

The size of these hydroelectric dams (and the amount of water and sediment trapped behind them) makes removing the Elwha River dams more complicated than some other dam removal projects. Together, the reservoirs behind the dams have the capacity to contain 48,600 acre-feet of water . There is also over 17 million cubic yards of sediment that has built up over the last 90 years. Special care must be taken in the dam removal process to minimize the negative effects that may occur with the release of that much water and sediment.

For the smaller Elwha Dam the first part of the removal project is the construction of a diversion channel, which will lower the level of Lake Aldwell by 50 feet. Once the level of the reservoir is lowered in this manner, the construction team will be able to remove the Elwha Dam by controlled blasting.

However, the 210-foot Glines Canyon Dam, which is double the size of the 105-foot Elwha Dam, will require additional measures to account for the larger quantities of water and sediment in Lake Mills. First, the reservoir level will gradually be drawn down using an outlet pipe to move water downstream. As the water level drops, demolition crews will cut and remove 7.5-foot sections of the dam starting from the top. These concrete blocks will be transported offsite by truck and recycled. Finally, once the sediments behind the dam are reached, controlled blasting will be used to clear the remainder of the dam.

The removal strategies are designed carefully to minimize negative effects (such as flooding and decreased water quality from sediment releases), but the precautions cannot completely eliminate these effects. Most of the effects are expected to be temporary, but some infrastructure changes will need to be implemented prior to dam removal to ensure that the water supply remains safe and steady. For example, a water filtration system will be constructed down river in order to maintain the supply of water to the city of Port Angeles.

Transition Period

When the dams were built, some watershed impacts were immediate (such as the elimination of salmon stocks in the upper watershed) while some other effects have developed over the last 90 years (such as the sediment deprivation that has impacted the nearshore). Undoing these impacts and bringing back the health of the watershed will likewise take decades to realize once the dams are removed, although some effects will be noticeable in the near term.

Shortly after dam removal, salmon species from the Pacific Ocean will begin to recolonize gradually over 70 miles of habitat that was not accessible to spawning salmon when the dams were in place. Much of this habitat is within the bounds of Olympic National Park and is in excellent condition. It is estimated that within 30 years, the river will produce 390,000 salmon and steelhead each year.

After the dams are removed, the Elwha River will regain its natural form and vast areas of land that were covered by the reservoirs will be devoid of any vegetation. These riverbank areas will be quickly planted with native plants to begin revegetation. However, it will take decades to restore portions of that land to the forested landscape that existed prior to the dams.

Some immediate effects will be negative, although they are expected to be short term. For example, the sediments that were bound behind the dam will begin to migrate down river and eventually out to sea. It is expected this process will take place within 5 years. When the sediment is released initially, it may kill fish and other species in the river and decrease water quality. Additional restoration actions downstream will help to minimize the impacts from this enormous load of sediment. However, in the long term, the return of the natural flow of sediment will have many positive effects: improving spawning habitat, building up the nearshore area, and reducing the need to build up Ediz Hook artificially.