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Chinook salmon come home to Elwha River

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Brendon Bosworth | Aug 29, 2012 03:55 PM

Five months ago contractors ripped down the final remnants of the Elwha Dam, which along with its upstream counterpart, Glines Canyon Dam, has for a century been blocking the paths of salmon up the Elwha River, which winds through Washington State’s Olympic National Park and empties into the Pacific at the Strait of Juan de Fuca.

Before the dams were built, without fish ladders, in 1913 and 1927 respectively, wild chinook salmon, some as large as 100-pounds, had access to 70 miles of the Elwha and its tributaries. The dams cut their spawning ground to the first five miles of river from the mouth, which drastically curbed spawning rates. Before the dams were installed, some 390,000 fish spawned in the river annually. This number dropped to just 3,000 while the dams were in effect.

When complete, the unprecedented deconstruction of these dams will open the salmon’s range to that enjoyed by their early ancestors. But it also comes with a biological price tag since vast quantities of sediment have built up in the dams over the years. Combined, the termination of the dams will release about 24 million cubic yards of sediment - enough to pack into a football stadium two miles high. And while some of the coarser components, such as gravel, will sink to the riverbed, providing essential habitat for salmon to spawn, the finer material – silts and clays – that turn the river water brown poses a threat to the salmon’s survival, explains Brian Winter, Elwha project manager for Olympic National Park.

Elwha The time the sediment will take to flush out to sea could vary between three and five years, depending on rainfall and stream flow in the coming winters, he says. Research into how the release will affect marine life is ongoing (as seen in this video of USGS researchers scouting the seafloor in scuba gear).

To shield fish from the impacts of the unleashed sediment, Barnard Construction, the Montana company contracted to pull down the dams (at a cost of $26.9 million) is working around a set of “fish windows” – periods where deconstruction does not lower dam height and allow sediment to escape. Until the current window ends in mid-September, work is being done to dismantle a 115-foot intake tower at Glines Canyon Dam.

Biologists from the state and Lower Elwha Klallam tribe are also collecting fish, including coho salmon and wild steelhead, from the lower river regions to rear in hatcheries and then releasing them upstream of the dam sites, before the next stage of deconstruction takes place, says Winter. To help protect the new fish populations there is a five-year moratorium on fishing in the river, which started last year.

A bunch of sediment waits behind the walls of the diminishing Glines Canyon Dam, and it will be some time before the river has stabilized, but chinook salmon have already started exploring parts of the river that were previously off limits and have been spotted close to the remains of the Glines Canyon Dam 12.5 miles upstream from the river mouth. Juvenile Chinook salmon were also seen at the park’s boundary when biologists were doing a snorkel survey, reports Peninsula Daily News.

These early visitors offer promise for how future generations of wild fish will repopulate the river during spawning season, but it will be some time -- as long as 28 years based on current estimates -- before numbers return to levels seen before the existence of the dams.

Brendon Bosworth is a High Country News intern.

Image: Site where Elwha Dam used to stand, courtesy National Park Service

 

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