In 1910, Thomas Aldwell began building the first of two dams across the Elwha River on Washington’s Olympic Peninsula. His dream was to provide clean, cheap hydropower to nearby Port Angeles. This September, the federal government will start to blow up those dams. Native Americans and fish biologists dream of freeing the river and seeing the Elwha’s legendary wild salmon runs return.

Bold, visionary action or federal boondoggle? You can find people who feel both ways about the biggest dam removal ever in the United States.

The Elwha’s watershed has an area of 321 square miles, 80 percent of it within Olympic National Park. Glacial meltwater crashes down from Mount Olympus through old-growth forest that will never be logged, through a valley that alternates between deep, narrow gorges and open bottomland. Although the Elwha is only forty-five miles long with a hundred miles of tributary streams, it is one of the Northwest’s most famous salmon rivers. Historically, the Elwha had ten runs of anadromous fish — spring and fall chinook, coho, pink, chum, and sockeye salmon, plus summer and winter steelhead, sea-run cutthroat trout, and sea-run bull trout. (Many larger Northwest rivers have only two or three of these fish species.)

Four hundred thousand salmon, more or less, returned every year, until the Elwha Dam was completed in 1913 and completely blocked salmon from all but the lower five miles of the river. Run after run of salmon bashed themselves against the 105-foot-high concrete barrier, trying to find a way upriver. A fish hatchery built as a “replacement” for the river was unsuccessful, and was abandoned in 1922. Remnant salmon runs, numbered in the tens or hundreds, struggled to survive in the fragment of river they could still reach.

The dams blocked more than salmon. The Elwha flows from steep, geologically active mountains and during floods the river carries tons of cobbles, gravels, sand, and dirt (all from natural processes within the national park) downstream. Since the second dam was finished in 1927, the river dumps that bedload, an estimated 180,000 cubic yards per year, in the slack water of a reservoir. Below the dams, the river is starved of the raw materials that build riverbeds, gravel bars, and spawning habitat for salmon. The beaches at the river mouth have eroded, losing 75 to 150 feet since 1927. The saltwater shoreline has receded and steepened, with the beach now made of stones instead of sand. To the east, Ediz Hook, a long, curved sandspit that protects the harbor of Port Angeles, erodes without new sand provided from the river. Now, the Army Corps of Engineers spends over $100,000 a year to control erosion on the spit, a service the Elwha used to provide for free.

Also, the dams starve the river of driftwood logs, the fallen trees that drift downstream and form logjams, the building blocks of deep pools and cover for fish. And with the salmon unable to swim upstream, the upper watershed is deprived of the nutrients in the salmon’s bodies. In undammed salmon rivers, scientists have found that up to 30 percent of the nitrogen in the upstream food web derives from ocean sources — carried upstream in the bodies of spawning salmon.

The Elwha River was not dead. But the once dynamic river was fixed, its potency cut by the dams. Yet some people, from the Elwha S’Klallam Indian tribe and from environmental groups, dreamed that the river could be free. An idea that seemed like late-night bar talk gained strength, and in 1992 Congress passed a law authorizing full restoration of the Elwha River ecosystem, a law that included the purchase and removal of the dams.

Progress was slow but steady. In 2000, the federal government bought and began operating the two dams and hydroelectric projects. Work began in 2007 on a water treatment plant to clear turbidity from dam removal from Port Angeles drinking water. A few weeks ago, the hydropower generators were shut down.

Actual dam removal will begin soon, on September 17. It won’t be as dramatic as a building implosion; the deconstruction will take at least three years. But chunks of concrete will start coming out, and there will be no going back after September 17.

A smaller dam removal on Oregon’s Sandy River, east of Portland, has had encouraging results. When the Marmot Dam was dynamited in 2007, wild coho salmon swam upriver past the old barrier only three days later. Sediment accumulated behind the dam for decades was far less troublesome than scientists had predicted. The Sandy River “digested” the sediment without trouble, moving and shaping it into gravel bars and banks.

The Elwha dam removal, however, is a gorilla compared to the Marmot Dam removal. Marmot Dam was 47 feet high; the two dams on the Elwha are 105 feet and 210 feet respectively. Marmot Dam had one million cubic yards of sediment accumulated in its reservoir; the two Elwha dams have a combined total of about 17 million cubic yards of sediment built up in their reservoirs. “Expect surprises,” one scientist has said.

What we really want to know about removing dams is this: Can we undo what we’ve done to a wild river? If we unlock a river, can a watershed rebuild itself? After a century without salmon, what happens when salmon return?

The Elwha River will be this country’s biggest attempt yet to answer this question. I’ll be there in September to witness it.

via Free Flow: Will the Biggest Ever Dam Removal Return the Wild to the Elwha River? | OnEarth Magazine.