Biggest dam removal in U.S. history will look like this
Nobody figured the largest dam removal project ever attempted in the U.S. was going to be easy -- or fast.
In fact, though the official demolition started Saturday, it will take two or so years to completely remove both dams on the Elwha River in Washington state, engineers say.
That allows for a gradual dismantling that will give the river time to settle into a new pattern. That way, it won't send a sudden flood of backed-up sediment rushing downstream, choking the very fish that officials are trying to help.
Jeff Duda, research ecologist for the U.S. Geological Survey, said in an interview that deltas containing 24 million cubic yards of sediment have formed behind both Glines Canyon Dam and Elwha Dam.
Somewhere between 25% and 50% of that will get carried downstream. Botanists will try to plant over the rest with new vegetation and keep it where it is.
The channel will be allowed to find its own way through the river's large functional floodplain, added George Pess, fisheries biologist for the National Oceanic and Atmospheric Administration.
What will the gradual demolition look like? Check out the visualization above, developed by Interactive Earth of Port Angeles, Wash., where the Elwha meets the sea a few miles down from the dams. It depicts the demise of all 210 feet of the Glines Canyon Dam, which is now, slowly but surely, underway.
--Kim Murphy in Port Angeles, Wash.
Video credit: David Zelenka, Interactive Earth