A river unleashed | Science News

Removing a dam involves more than impressive explosions. Releasing a river like Washington state's Elwha transforms the landscape and restores important pathways for native fish. Read the full story at sciencenews.org: https://www.sciencenews.org/ar....ticle/dam-demolition

Engineers built a pair of dams along the Elwha about a century ago to capture its waters and provide hydropower to a nearby timber and paper mill operation. Both dams were recently dismantled as part of a broader push, across the United States and elsewhere, to remove aging dams. This video explores the removal of the dams on the Elwha River.

Script:

Narrator: With a bang — well, a series of them — the concrete fortresses of two giant dams holding back the Elwha River have come crumbling down. Dismantling the dams over the last few years in Washington State has been called the great Elwha Experiment. It’s a rare chance to watch what happens when a mighty river runs free once again, says Jeff Duda, a research ecologist at the U.S. Geological Survey.

Duda: There’ve been over a thousand dam removals in the United States, but the Elwha really stands out for a couple of reasons. One is the size of the dams. There were two large dams that were removed, just in terms of their height. The amount of sediment being released as part of the project is also unprecedented. And then the fact we’re standing in Olympic National Park and the majority of the watershed is protected as wilderness really is another facet of the project that really makes it one of a kind.

N: The two dams that came down were the Elwha Dam, which was finished in 1913 and stood 33 meters high, and the Glines Canyon Dam, which was completed in 1927 and was a towering 64 meters tall. They were built to provide electricity for a paper mill. They served their purpose. But they also disrupted salmons’ long swim up river to spawn. When the dams were constructed, ninety percent of the salmon habitat was cut off and the fish populations plummeted. Taking down the dams, however, is quickly correcting the population problem.

D: Connecting the upper river to the lower river and giving salmon the opportunity to recolonize their former spawning ground that they didn’t have access to for over a century is something we are really interested in learning about and understanding.

N: Duda says that salmon wriggled their way far up the river just after engineers blasted the final remnants of the Glines Canyon Dam. And already scientists are seeing nearly triple the number of salmon spawning nests downstream. There are other changes too. When the massive amounts of sediment trapped by the dams—enough to fill more than five Wembley stadiums—were released into the lower river, it settled into sandbars where new grasses and shrubs are starting to grow and reshape the river.

Remnants of the Glines Canyon Dam, however, still remain.

D: I think it will be a historical landmark as reminder of the history of this spot and the history the dams played in shaping the Elwha River.

Images and Video:
John Gussman, www.elwhafilm.com; Alexandra Witze;
Library of Congress, Wikimedia Commons, Public Domain

Reported by Alexandra Witze
Narrated and produced by Ashley Yeager