PORT ANGELES — A key step in the estimated $350 million Elwha dams removal project will happen within the next 10 days.
Lake Mills will be closed to recreational boating, fishing and swimming while workers dig a giant channel through which millions of yards sediment will flow.
A precise closure date of Lake Mills will be set once the channel-digging contract is completely negotiated and signed, said Olympic National Park spokeswoman Barb Maynes.
The closure was originally set by the park for next Thursday, Aug. 26.
The lake is expected to be closed to boating for about eight weeks.
A section of the Elwha River between the lake and Goblins Gate also will be closed, Maynes said.
Closure of part of the Elwha River will force kayakers and other boaters to exit at Goblins Gate and hike out using the Rica Canyon Trail and Elwha River Trail to the Whiskey Bend trailhead.
In addition, heavily used and easily hiked two-mile West Lake Mills Trail, which begins at the lake’s soon-to-be-closed boat launch parking area, will be closed.
That will begin around Aug. 30 so a pilot channel can be dug through the delta at the head of the reservoir to release sediment piled behind the dam and enhance the river’s salmon habitat, Maynes said.
Lake Mills will be lowered 5 feet, its waters emptying over the dam’s spillways to expose the delta and allow workers to dig with heavy equipment on drier ground, Brian Winter, Elwha River Restoration Project manager, said Thursday.
Lake Mills is a fishing and recreational boating reservoir that sits behind Glines Canyon Dam, sister to the Elwha Dam, both of which will be torn down beginning in September 2011 and ending in March 2014.
It is the largest dam removal project in U.S. history and will free the Elwha River after 100 years.
The goal is to restore salmon populations and the river’s ecosystem.
Olympic National Park has been promoting this summer as “the last dam summer.”
As the Glines Canyon and Elwha dams are torn down, sediment will gradually coat the riverbed of the Elwha River.
That redistribution of sediment is the crux of the Elwha River Restoration Project, Winter said.
It will take three to five years for the sediment to settle, he said.
For a century, the dams have blocked sediment from providing nooks, crannies and cover necessary for salmon eggs to thrive in all but five miles of the river from the Elwha Dam to the Strait of Juan de Fuca.
“Only about a third of the coarse material and sand and gravel will make it all the way out to the Strait,” Winter said.
“The rest will be spread out like a paintbrush.”
The sedimentation project that will begin soon is “another sign, it’s another signal that the change is coming, and it’s coming now as we make preparations for dam removal,” Maynes said.
The dug channel will carry sediment that will be released as the dams are removed to revive the river’s severely depleted salmon stock.
At least 18 million cubic yards of gravel and dirt is piled behind the dams — 13 million behind Glines and 5 million behind Elwha.
“Once dam removal begins, the river will carry large amounts of sediment downstream, where it will restore fish habitat, shellfish beds and beaches along the Strait of Juan de Fuca,” Olympic National Park Superintendent Karen Gustin said in a statement.
“Creating a pilot channel and removing trees from the delta will give the river the head start that it needs to erode the sediment.”
The project must be completed before the rainy fall season “so we can maximize winter erosion, accomplish the work safely and be prepared for the dam removal to begin next year,” Gustin said.
Once the channel-digging contract is signed, workers will begin barging heavy equipment to the south end of the lake to remove trees and will begin digging away.
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Senior Staff Writer Paul Gottlieb can be reached at 360-417-3536 or at paul.gottlieb@peninsuladailynews.com.
