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Field Notes

Covering the natural wonders of the Pacific Northwest

July 31, 2012 at 9:00 AM

The underwater world of the Elwha: a new ecosystem takes shape

Divers took the plunge last week to investigate the effects on the nearshore environment of dam removal on the Elwha River. Here is a video published by USGS of the dive.

For some amazing photos of what divers are seeing, check out this link.

The divers were returning to permanent transects they established before dam removal in and around the Elwha, in order to be able to survey and monitor how the sea floor is changing as dam removal progresses, notes Jeff Duda research ecologist with the US Geological Survey Western Fisheries Research Center in Seattle.

“We are identifying species and counting abundance of kelp, macroinverts and fish. Not salmon, they are higher in the water column.” Duda said. “But fish closer to the sea floor, such as gunnel.”

diving photographer.jpg

USGS Scientific diver Steve Rubin begins video recording of a permanent seafloor transect that will be monitored before, during and after dam removal on the Elwha River.

Photo by Sean Sheldrake, EPA

“The idea is to see the sediment as it is coming out of the river and eventually the return of a more natural sediment regime in the future,” Duda said.”You see these dramatic photos of sediment plumes in the Elwha, but that is just what is happening on the surface. It is just the first ten feet or so. By and large the plume is buoyant.”

The real story is under the suface.

cool tube worm.jpg.

The Elwha River seafloor on July 26, 2012, with an anemone and a field of tube worms and other aquatic life.

Photo by Sean Sheldrake, EPA

“Not as much deposition has happened as you would expect just looking at the plume. We were a little surprised. Glines Canyon has not come out yet and we will see a lot more then,” Duda said.

Based on preliminary results, about 87 percent of what scientists are seeing in the water column in monitoring samples taken in the river is fines: clays and silts. The whole bottom of the river, meanwhile, is like a conveyer belt, moving heavier cobbles and even, during very high flow, boulders. But it takes a lot longer for the big stuff to reach the coast. “This is the early part of the story,” Duda noted.


Scientific divers from USGS and Washington Sea Grant prepare for a dive off the mouth of the Elwha River as part of long-term monitoring of life on the sea floor before and after dam removal.

Photo by Paul Laustsen, USGS

Dives will be just one way to understand the emerging ecology of the seafloor and riverbed as dam removal continues. Scientists are relying on a wide variety of monitoring techniques to track changes in the Elwha. They have even placed metal plates in the river to listen to the transport of rocks, gravel and sediment in the river.

Elwha Dam, the lower of two dams built in the Elwha without fish passage beginning in 1910, was completely removed as of last March. The biggest slugs of sediment are actually expected to be released into the river beginning next year as the material stuck behind Glines Canyon Dam begins to cut loose.

The dams together blocked not only ocean going runs of fish — all five runs of native Pacific salmon, as well as steelhead — but the flow of sediment and wood down the river. Restoring the river’s transport capacity is one of the most important aspects of restoring the river’s natural function and processes.

More than 24 million cubic yards of sediment — enough to fill an NFL stadium eight times, were trapped by the dams over the past century. As of July, about 400,000 cubic yards of sediment has been released. As it is released by dam removal, the sediment is changing the structure of the riverbed and estuary where the river meets the Strait of Juan de Fuca.

High concentrations of sediment and turbid conditions are expected to persist for about five years as dam removal is underway. In the near term, that is expected to be hard on life in the water and on the bottom, but in the long term, the near shore, starved for sediment, is expected to rebound — and eventually be richer in life than before.

Already, scientists working in the Elwha see changes. It used to be walking the Elwha for scientific surveys meant navigating ankle-turning cobble. Now, it means walking in water so cloudy with released sediment the water is opaque.

“There is a new Elwha gait that has developed,” said Duda, recently back from baseline monitoring work in the river. “You can’t see your feet.”

For a spectacular slide show on life on the undersea floor in the Elwha near shore, see this link.



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