OLYMPIC NATIONAL PARK — Work to remove massive boulders in the Elwha River near Glines Canyon in order to ease fish passage has been completed.
Sealaska Constructors LLC recently finished the National Park Service contract to remove large boulders from the river just downstream of the canyon, according to an Olympic National Park news release.
Between Aug. 31 and Oct. 8, a total of seven controlled blasts reduced about 14 large boulders — most weighing over 100 tons — into pieces less than two feet in diameter.
While all the rocks were larger than what the river would move downstream, the two largest were each as tall as a two-story building, about 30 feet wide and estimated to weigh at least 1,000 tons.
Park scientists will continue to monitor the river channel through the coming high-flow season and will assess the river channel next summer.
By comparing historic and recent photos and water levels, geologists determined that a large rockfall produced the boulders at some point after Glines Canyon Dam was completed in 1927 and before dam removal began in 2011.
A significant portion of the canyon’s east wall broke off, sending large boulders into the river channel, slowing and changing the river’s flow through the area.
The dam removal process restored the river’s natural flow, allowing it to carry sediment downstream from the former Lake Mills reservoir.
The boulders in the channel caused sediment and debris to accumulate above the rockfall, creating a barrier to upstream fish passage.
Chinook, steelhead and bull trout are known to have migrated above the Glines Canyon site, with some reaching as far upstream as Geyser Valley.
Removal of the boulders will further restore the river channel through Glines Canyon, aiding the overall restoration of the Elwha River.
Project funding was provided by NOAA Fisheries and the National Park Service, and the contract was included in the $325 million Elwha River Restoration project cost.