Salmon are headed upstream in the Elwha River for the first time in more than a century, but sediment—and lots of it—is headed downstream. The sediment is the result of the largest dam removal project ever undertaken.
The 108-foot Elwha Dam, built in 1910, was dismantled last year, resulting in about 34 million cubic yards of sediment. That’s more than 3 million truck loads—enough to cover Seattle in a layer almost 3 inches thick. For the past five years, UW oceanographers have been studying the sediment around the river mouth to understand conditions before the dam’s removal. They are now focused on tracking the movement of the sediment and its ultimate fate. Where the sediment ends up is of practical interest.
Sediment can make the water murky, creating conditions that make it difficult for salmon to lay eggs, or block light from reaching algae and other life on the ocean floor. The sediment also has positive impacts. Many people hope that removing the dam will help with erosion along the Olympic Coast.
Nobody knows when the Elwha’s sediment mother lode will begin to shift, but UW oceanographers will be ready to hop in their van, hitch up a boat and follow the action. Follow the project on the research blog of the UW School of Oceanography Sediment Dynamics Group: blogs.uw.edu/sediment/