The Pilchuck River has already taken one home and now threatens State Route 92 west of Granite Falls, Washington. But an AquaDam and river stabilization plan should mitigate further damage.
The Washington State Dept of Transportation has started in on a $3.2 million project to stabilize the riverbank and protect the highway.
“The riverbank is now within 40 ft of the road,” says Dave Lindberg, WSDOT project engineer. “If we don't stop this erosion now, we run the risk of losing the highway.”
Beginning today, contractor crews from Marshbank Construction Inc. will install an AquaDam to temporarily divert the river from the work zone. The water-filled dam was first used in the early 1980s as an alternative to the slow and cumbersome sandbagging process. By filling massive bladders with water, the AquaDam will grow large enough to move the Pilchuck River away from the work zone, allowing crews to then create a permanent protective barrier of rocks, logs, root wads and plants.
The final goal offers a more stable bank that prevents the continual erosion toward the highway while also replanting vegetation previously lost to the river. The return of the plants and trees will also help prevent further erosion and improve wildlife habitat.
Between 2006 and 2009, the riverbank receded 130 ft, mostly during a record-setting flood in January 2009. A house eventually fell into the river in 2012. Since then, the riverbank has continued to erode 30 to 40 ft per year, and it is now less than 40 ft from the edge of the highway.
The continued undercutting of the bank and a gravel bar in the water has changed the bend in the river. In addition to advancing closer to the highway, the river is now approaching another home and pasture downstream. The erosion control work will not only protect the highway, but nearby properties as well.
Work will mainly occur weekdays and is planned to wrap up by early fall.
Follow Tim Newcomb on Twitter at @tdnewcomb.