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Article published Jan 20, 2013 A little more Peninsula; a little less Strait: Free-flowing Elwha River silt grows beaches near mouth
By Jeremy Schwartz Peninsula Daily News
At least one scientist monitoring the shoreline surrounding the ever-evolving mouth of the Elwha River has started to see modest beach growth as sediment held back by two gargantuan dams for nearly 100 years is released during the dams’ removal.
As sediment from the destruction of Elwha Dam and the ongoing removal process of Glines Canyon Dam 8 miles upstream flows toward the Elwha River mouth, it accumulates in sand bars that are shaped nearly every day by the flow of the river, said Ian Miller, a coastal hazards specialist and one of the scientists surveying beaches to the east and west of the river mouth.
Miller said he regularly surveys four sites in the immediate vicinity of the mouth: three just to the east and one just to the west.
During his most recent survey trip Jan. 13, Miller said the beaches at the site roughly just to the east of the Elwha’s mouth are growing slightly and are becoming sandier as more sediment is released.
“There’s still gravel and cobble, but [the beach] is sandier than it was before,” Miller said.
Miller said he also noted the river mouth had changed direction within about a month, from a survey trip in December to the Jan. 13 outing, and had completely broken through one of the sand bars formed from accumulated sediment.
“That’s the thing that’s notable about the Elwha: It’s [that] you can go back in two weeks, and it’s all different,” Miller said.
“A lot of funky things are happening in terms of morphology of the river mouth.”
Miller said the ultimate goal of his surveying work and that of others scrutinizing the beaches to the west and east of the mouth is to figure out how much Elwha sediment is reaching the surrounding shorelines and if it stops or reverses beach erosion that has been documented for decades.
Farther upstream to the south, a team of scientists from Olympic National Park and the federal Bureau of Reclamation last week traversed the former Lake Mills — now drained as the removal of the once-210-foot Glines Canyon Dam continues — and the middle stretch of the river between Glines Canyon and the former Lake Aldwell, said Andy Ritchie, a park hydrologist and one of the members of the surveying team.
Ritchie said the team has been seeing fine-grain sediment coating the bed of the former Lake Mills, enough that hikers trekking some of the trails overlooking the upper part of now-drained lake could be able to see sediment deposits remaining from this autumn and winter.
“If you look across the river, you can see [the deposits] outcropping on the other side,” Ritchie said.
Farther upstream closer to the south end of the former Lake Mills, Ritchie said the five-person team saw larger-grain sand, pebbles and cobbles that have not yet been pushed downstream by the newly freed Elwha River.
“We’re trying to determine how rapidly the gravel versus the sand is moving down the river,” Ritchie said.
Ritchie said the point of surveying trips like these is to help determine if the river can handle the additional sediment that would be released once removal of Glines Canyon Dam begins again.
The scientists involved are still in the process of analyzing the data, Ritchie added.
“We have collected a lot of data, and we’re still trying to answer that question,” he said.
Olympic National Park spokeswoman Rainey McKenna said Friday that managers of the continuing dam-removal project will take the sediment teams’ recommendation into account when deciding when to restart tearing down Glines Canyon Dam, though no dam-removal work will begin sooner than Feb. 4.
The Elwha Dam was removed last spring.
May is the expected completion date for removal of Glines Canyon Dam.