Behind The Elwha Dams: The Drawdown of the Aldwell and Mills Reservoirs

For the first time in nearly a century, the man-made reservoirs behind the Elwha River’s two fish-blocking dams are starting to look like riverbeds once again.

The Aldwell and Mills reservoirs have been lowered 20 feet this summer in advance of the upcoming removal of the 108-foot-tall Elwha and 210-foot-tall Glines Canyon dams.

New river channels are forming in the deltas of the reservoirs behind the Elwha River dams, as seen here in the south end of the Aldwell reservoir.

“The deltas of the Aldwell and Mills reservoirs are exposed and new river channels are forming,” said Mike McHenry, the tribe’s fisheries habitat manager. “Reservoir shorelines that have been underwater for decades are finally being exposed, revealing old sandbars and stumps from logging.”

A top priority of the reservoir restoration project is to prevent invasive plant species from entering the national park, McHenry said. More than 150 exotic species have been identified within the Lower Elwha watershed. As the dams are removed, the tribe and the National Park Service will remove invasive species, such as Scot’s Broom, St. John’s Wort and canary grass, found on the reservoirs’ shorelines.

Within the two reservoirs, restoration crews will seed 261 acres and plant native vegetation on 440 acres including dogwood, cottonwood, willow, alder and Douglas fir.

The Elwha and Glines Canyon dams are owned by the federal government; the Olympic National Park is spearheading the removal effort. The project to remove the structures and restore the Elwha River ecosystem, estimated at $350 million, is the largest dam removal project to date in the United States.

Built without fish ladders, the dams have been in place since the early 1900s and prevented fish from moving past the lower 5 miles of the river. During the next three years, the dams will be removed initially in 7.5-foot sections, then by controlled blasting. Deconstruction starts September 2011.