Sediment forming sandbars at Elwha River mouth
Waves break on sandbars at the mouth of the Elwha River on Dec. 18 as an aerial photograph shows sediment coming into the Strait of Juan de Fuca.
By Jeremy Schwartz
Peninsula Daily News
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In a yearlong dam removal and restoration project, scientists observing its progress are witnessing the formation of sandbars at the mouth of the river, a sign of the Elwha's slow return to its natural processes and an indicator of sediment flows that haven't been seen in decades.
“Everybody has been modeling and mapping and anticipating this event for probably 20 years,” said Anne Shaffer, a marine biologist and coordinator with a group of scientists, called the Elwha Nearshore Consortium, organized to observe the restoration project.
Shaffer said the formation of sandbars at the river mouth is one of the clearest signs of how much sediment, once locked behind the massive Elwha and Glines Canyon dams, is coursing down the river.
Construction crews have removed the Elwha Dam, which stood for nearly 100 years just south of Port Angeles, and are working toward the final demolition of its bigger brother, the Gllines Canyon Dam 8 miles upstream, which is slated to be completely demolished by May.
A combination of lakes created by the dams being completely drained and heavy rains over the past few months have sent pulses of caramel-colored sediment into the azure waters of the Strait of Juan de Fuca and have started to form the sandbars, which are often clearly visible from the air.
“I don't think anybody anticipated it would be this visual,” Shaffer said.
“It's just striking.”
Scientists on the project estimate the two dams held back 25 million cubic yards of sand, silt, cobble and gravel.
Only about 10 percent of that has found its way to the mouth of the river or into the Strait, said Ian Miller, a coastal hazards specialist with Washington Sea Grant and one of a small army of researchers surveying beaches on either side of the Elwha's gaping maw to see where the sediment is going.
“We still think that we're just at the tip of the iceberg when it comes to sediment delivery,” Miller said.
On a recent sediment- surveying trip, Miller said he documented sandbars growing 25 vertical feet from the river bottom.
That meant that he could easily walk in an area that was once underwater.
“Last week, I was able to walk a couple of hundred yards out to a place I previously would have had to scuba-dived to see,” he said.
Dave Parks is a state Department of Natural Resources geologist and wetlands scientist.
Parks, who is studying how the sediment reaches beaches east of the river mouth, said the varying amounts of sediment flowing out of the river will change the profile of the bars on an almost daily basis.
That means that what Miller walked on one week might not be there the next.
“We expect the mouth to be highly dramatic over time,” Parks said.
“[It] will change with every tide and every river discharge.”
Scientists are seeking to answer two main questions:
-- Will the sediment from the Elwha halt or reverse erosion of the surrounding beaches?
-- Will the amount of sand and other sediment comprising these beaches drastically change as a result of the river's sediment flows?
“We're measuring beach profiles, and we're measuring grain size,” Miller said.
The shorelines surrounding the mouth, especially those to the east, have been effectively sediment-starved for almost as long as the dams have been in place, Miller esaid.
This led to chronic beach erosion documented as far back as 1939.
With the dams removed, scientists expect the river to once again provide a yearly sediment supply to these shorelines, and Miller said the daily changes he is seeing at the mouth are just the beginning.
“These are very exciting changes, but we don't yet understand yet what the long-term changes are,” Miller said.
Parks, who has been monitoring the beaches between the mouth of the Elwha and the western edge of Port Angeles — shoreline that runs below the Port Angeles Transfer Station and former landfill — said he has begun to see changes in the grain size and the accumulation of woody debris at these beaches but no major alterations in the beaches' shape or length.
Eventually, Parks said he and other scientists expect to see the beaches get less steep and become finer grained as sediment from the Elwha accumulates there, though he could not estimate how long the process could take.
“Ultimately, it's still an open question how fast [the sediment] will come out,” Parks said.
Parks said some sediment also is expected to reach Ediz Hook, though no surveys are being done there, since those beaches are artificially maintained by the U.S. Army Corps of Engineers.
Miller said the Elwha restoration process will serve as tool to help scientists around the world figure out how natural marine shorelines can help protect coastal communities from storm surges and other damaging, high-water events.
“Being able to study dam removal on this scale, on a marine shoreline, is unique,” Miller said.
Shaffer said no other researchers in the world are getting the opportunity they are to watch a nearshore ecosystem slowly recover after nearly a century worth of concrete and steel has stopped up the river's natural processes.
“This is unprecedented for a restoration event,” Shaffer said.
“It's never been seen before, ever.”
Reporter Jeremy Schwartz can be reached at 360-452-2345, ext. 5074, or at firstname.lastname@example.org.
Last modified: December 25. 2012 5:12PM