Tracking sediments fate in largest ever dam removal
Marine geologists are watching what’s beginning to flow downstream
“A surface plume is very much at the whim of the winds and tides, whereas these underflows are just going down the steepest gradient,” Ogston said. “These are two very different mechanisms that would create very different impacts to the seabed.”
Tracking sediments fate in largest ever dam removal
By Hannah Hickey
News and Information
Salmon are beginning to swim up the Elwha River for the first time in more than a century. But University of Washington marine geologists are watching what’s beginning to flow downstream — sediments from the largest dam-removal project ever undertaken.
The 108-foot Elwha Dam was built in 1910, and after decades of debate it was finally dismantled last year. Roughly a third of the 210-foot Glines Canyon Dam still stands, holding back a mountain of silt, sand and gravel.
Removal of the upper dam was halted in January while crews repair a water-treatment plant near Port Angeles that got clogged with leaves and other debris. For engineers, this phase may be the trickiest part of the dam-removal project. For oceanographers, “the best is yet to come,” said Charles Nittrouer, a UW professor of oceanography and of Earth and space sciences.
It turns out there is even more sediment than originally thought – about 34 million cubic yards. That’s more than 3 million truck loads, enough to bury all of Seattle in a layer almost 3 inches thick.
Aerial photos show sediment starting to fan out around the river’s mouth.
“One of the risks of just looking at these beautiful plume pictures is that you really don’t know the extent of where that sediment actually ends up,” said Andrea Ogston, a UW associate professor of oceanography. “Our focus is looking at what’s happening very close to the seabed – how it’s going to move, where it’s going to get to, what’s its ultimate fate.”
