Rebirth of the Elwha River
On August 26, workers blasted out the final section of the 64-m Glines Canyon Dam on Washington State's Elwha River, completely freeing 110-plus kilometers of streams – largely within Olympic National Park (ONP) – that a century ago supported some of the Pacific Northwest's most prolific salmon fisheries. The biggest US dam removal project ever undertaken (it also entailed demolishing the ~33-m Elwha Dam lower on the river), it began in 2011 following three decades of legal and political wrangling between government agencies, the Lower Elwha Klallam tribe, and river conservationists.
“The pace of the coastal recovery has been exciting and fascinating”, says USGS geomorphologist Jonathan Warrick (Santa Cruz, CA). To date, the river has eroded about one-third of the roughly 20 million cubic meters of sediment previously trapped behind the dams, moving over 95% of it downstream to form a massive new river-mouth delta and spill out into nearshore ocean waters. “Over the past 100 years, due to the dams, approximately 200 m of coastal shoreline eroded away, but since 2011, half again as much land [ie 300 m] has been rebuilt in the same area, creating habitat for crabs, bait fish, clams, and other species”, he explains. In time, the Klallam may once again harvest shellfish there.
Signs of transformation are equally apparent upstream. “Willows, alders, and other riparian plants are recolonizing the reservoir beds, which resembled a moonscape only 2 years ago”, says ONP ranger Denison Rauw. Additionally, more than 67 000 seedlings have been planted to restore native vegetation. “The river itself is recreating prime fish habitat by redistributing woody debris and building gravel bars and deep pools”, she adds. Biologists radio-tagging salmonids migrating from coastal waters have recaptured them many kilometers upstream, fueling optimism that fish numbers could rebound to pre-dam levels (annual runs approaching 400 000) within 20–30 years.
Adult salmon and their eggs, fry, and carcasses provide nutrient-rich sustenance for all kinds of insects, birds, and mammals; dippers and other aquatic species have been quick to take advantage of the newly available prey. Scientists have shown that the salmon's bounty is spread across the forested watershed, and researchers examining tree stumps in the Elwha basin have discovered that the tree rings in the Elwha Basin were narrower during the time period when the dams largely excluded salmon from the river. “The efforts of so many people have come to fruition”, Rauw muses. “Now the powerful Elwha River is restoring itself, and we get to witness this transformation.”