Dam fascinating: DNR’s nearshore team studying what happens to marine vegetation during and after Elwha River restoration

Aerial photo of the Elwha River delivering sediments to the Straits of Juan de Fuca. Photo: Tom Roorda
Sediment pours out of the Elwha River into the Straits of Juan de Fuca. Photo: Tom Roorda.

Just west of Port Angeles, an unprecedented scientific experiment is taking place on a grand scale. Researchers from a variety of disciplines are watching and studying what happens following the removal of the two large dams on the Elwha River.

Since the removal of the entire Elwha Dam and part of the Glines Canyon Dam last year, millions of cubic yards of sediment, held back by the dams for 100 years, have spilled down the course of the river and oozed out along the shoreline in the Straits of Juan de Fuca.

Photo of Helen Berry, DNR nearshore scientist.
Helen Berry, DNR nearshore scientist, has been studying the effects of Elwha dam removals on nearshore ecology and marine vegetation.

Scientists from DNR’s Nearshore Habitat Program want to know how the escape of these sediments will affect marine vegetation in the area.

In these early, post-dam days, they expected to see some changes; however…“What we’re seeing is a striking and dramatic impact from the outflow of sediments into the Straits,” says Helen Berry, DNR’s lead nearshore resource scientist.

During the dams’ rein over the natural flow of the Elwha, which effectivley stopped up sediments,  kelp beds became the dominant vegetation in the marine shoreline’s rocky substrate.

“With the release of the sediments downriver into the nearby marine environment, we expected to see eelgrass and other seagrasses start to take hold, which they have,” Berry added. “But we also expected to see much of the kelp beds remain for the short term and mix with newly establishing seagrasses.”

Instead, much of the kelp in a 2,500-acre area near the mouth of the Elwha has decreased significantly. Already.

Interestingly, data from before the dams were built shows that eelgrass and seagrasses were the predominant marine vegetation in the area.

Eelgrass is a key “indicator species” that help us understand the health of estuaries such as Puget Sound and the greater Salish Sea.

So, is the area returning to a new, healthy normal? Only time and science will tell.

DNR’s Helen Berry has been interviewed in several recent stories about the Elwha River dam removals. Read more at:
• Seattle Times: Elwha gnaws away at a century of sediment (3/16/13)
• Seattle Times: Kelp Armageddon at the mouth of the Elwha (3/17/13)
• Kitsap Sun: Dramatic changes following Elwha Dam removal (3/2/13)

Learn more about the Elwha River Restoration and follow the Elwha Dam and Glines Canyon Dam removals with the Olympic National Park web cam.

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