PORT ANGELES — Its delta peak shaved last fall, an underwater sediment mountain at the mouth of Lake Mills is slowly being cut down to size as the Elwha River rushes into the reservoir that was created when the Glines Canyon Dam was built 84 years ago.
Four months later, the 50-foot-wide channel is now 180 feet wide on the south side and more than 355 feet wide in the middle, Olympic National Park spokesman Dave Reynolds said Thursday.
“What this project did was basically remove a plug,” Reynolds said.
But the real action begins when Barnard Construction Co. Inc. workers start dismantling the Glines Canyon and Elwha dams in mid-September in a mammoth task that will drain lakes behind both dams to return the river to a naturally flowing state.
Then, after September 2014, when deconstruction is complete, the delta at the lake’s mouth and more than 18 million cubic yards of sediment behind the two dams are expected to coat the riverbed and provide vital habitat for the Elwha’s storied salmon run.
The delta was stripped of trees last fall and a pilot channel dug through it, allowing the river to flow more effectively into the reservoir, centering the waterway’s course and cutting away at sediment that had blocked the river’s passage.
The channel will allow “more complete erosion of the sediment,” said Karl von Rosenberg, the National Park Service’s project director for the Elwha River Restoration Project.
The delta removal project started sediment erosion but “is not intended to move a lot of sediment at this point,” he said.
“That will really start occurring when the lake level begins dropping.”
Ever since the Glines Canyon Dam was built, the river has slowed as it enters Lake Mills, depositing sediment at the mouth that grew taller and taller until it popped above the water line and hosted 37 acres of alder trees.
Those trees were stripped off the delta in a week of tree-cutting and pilot-channel digging that ended Oct. 4.
Before that, the river split into three tiny tributaries as it entered the lake.
Now it’s flowing in a more predictable manner, said Elwha Dam power plant supervisor Kevin Yancy.
“By re-routing that channel, all the tributaries are flowing into one center stream to have the river more effectively flush out that sediment,” he said.
“If we would have done nothing, then that river would have been a little less predictable to see what kind of effect we would have had with that sedimentation.”
The net effect of the delta-digging project: “Re-routing that river,” Yancy said.
The 210-foot-tall Glines Canyon Dam was completed in 1927, while the 108-foot tall Elwha dam, eight miles downstream, was completed in 1913 and created its own reservoir, Lake Aldwell.
Both dams are salmon-unfriendly: Neither was built with fish ladders.
That cut off more than 70 miles of pristine habitat to salmon that migrate up rivers from the sea to spawn.
Before the dams were built, the run was said to have numbered 400,000 salmon, and historical accounts recall 100-pounders being caught.
Today, the salmon run has dwindled to 4,000, with just 4.9 miles of habitat between the mouth of the Strait of Juan de Fuca and the Elwha dam.
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Senior Staff Writer Paul Gottlieb can be reached at 360-417-3536 or at paul.gottlieb@peninsuladailynews.com.
