Trees felled in preparation for Elwha dam removal

An army of excavators has started ripping out a 37-acre grove of alder trees on the Olympic Peninsula's Elwha River in the first stage of what's being billed as the largest dam removal project in the nation's history.

The $350 million project begins in earnest in September 2011, when workers will begin to dismantle the 108-foot high Elwha Dam and the 210-foot high Glines Canyon Dam. The Elwha dams are nearly a century old and would be the largest of about 750 dams removed around the country.

Crews have a lot of work to do to ensure the project goes smoothly and allows salmon and steelhead to recolonize more than 70 miles of pristine habitat within Olympic National Park.

Workers with Cherokee Construction Services of Vancouver, Wash., shipped the heavy equipment to the south end of Lake Mills by barge and last week began clearing the grove where the river meets Lake Mills - a task that is expected to be completed this week. Once the trees are removed, workers can begin digging a channel to make sure the river heads in the right direction when the dams come down.

"The pilot channel is like a surgical tool, to just get things started in the right place," Tim Randle, of the Bureau of Reclamation's Denver office. "We thought that if we don't get it started in the right spot, you could have a lot of trouble later."

Plans call for the channel to be dug 1,100 feet long, 50 feet wide and 6 feet deep. It's necessary to make sure that the sediment caught behind the dam flows evenly downriver. Modeling experiments have shown that without it, as much as 80 percent of the sediment could be left behind when the dams come down, The Seattle Times reported.

An estimated 20 million cubic yards of sediment - the equivalent of 1 million dump truck loads - is locked up behind the dams. That sediment, once rinsed downriver, is expected to replenish spawning gravel needed by fish in the river, as well as beaches and clam beds.

Chinook are coming back to the Elwha in record low numbers this season, with fewer than 500 adults counted.

Mike McHenry, fish-habitat manager for the Lower Elwha Klallam Tribe, said the causes include the dams, which confine the fish to the lower five miles of the river and don't allow them to get to traditional spawning grounds; state hatchery practices; and flooding in 2006.

More than 2,000 chinook return in a typical year, he said.

Scientists hope the fish populations will rebound when the dams are out, with as many as 20,000 to 30,000 chinook returning each year. The fish are protected under the Endangered Species Act.

The dams will be removed gradually, and should be gone by March 2014.

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Information from: The Seattle Times and Peninsula Daily News