Situation
The Stillaguamish Tribe of Indians and the U.S. Forest Service initiated this project to restore salmon habitat in the South Fork of the Stillaguamish River by reducing the amount of sediment flowing into it from the Gold Basin landslide. The landslide deposited more than 40,000 tons of sediment annually into the river, ruining a spawning area for steelhead and salmon. The project involved the excavation of a new channel to move the river away from the massive alluvial deposit created by the landslide.
Solution
The completed work included moving the existing river channel away from the landslide’s three active lobes. Fourteen acres of second-growth timber were cleared and grubbed, and GBI worked with the Stillaguamish Tribe of Indians to repurpose it for the wood structures that now stabilize the new channel. This also reduced the costs of importing, handling, and processing off-site timber.
To create the new 250-foot-wide channel, GBI excavated 213,000 cubic yards of material. The material was then placed within the original channel to form six large settling basins that could capture and contain the silt from the three lobes. GBI also constructed 1,500 linear feet of live crib structures to support the new channel and keep it within its north banks. For the live crib structures, crews had to partially assemble, set, and backfill each section into excavated footings before they could be completed.
Notable
This project was three decades in the making, and it is of great importance to the Stillaguamish Tribe of Indians. GBI’s Washington Region worked closely with the Tribe from start to finish, and in spite of permitting delays and design changes, what was initially slated to be a two-season project was completed in one.
