Something as simple as a pile of logs and loads of dirt can change the dynamics of a river to benefit salmon.
Deep in the Skokomish watershed this summer, 1,100 trees were used to build 16 logjams in the South Fork Skokomish River. These strategically constructed piles of logs will restore salmon habitat in a 1-mile stretch of the river that was damaged by logging decades ago.
Tacoma Power purchased and logged this swath of land in the late 1950s to build a dam and reservoir, only to discover that an earthquake fault went straight through the property. The project was abandoned but logging had already taken place.
“River functions in the Pacific Northwest are controlled by wood,” said Rich Geiger, the Mason Conservation District’s engineer. “When an area adjacent to a river is logged, it changes the dynamics of the river.”
As a result, the Skokomish Tribe has seen the river channel shift or widen and become shallow because of degraded conditions. Woody debris and native vegetation keep riverbanks stable, and control sediment movement throughout the river, which plays a part in developing safe places for salmon to feed, hide from predators, and spawn.
“Even though this site is approximately 11 miles from the mouth of the South Fork, what happens upstream impacts everything downstream,” said Alex Gouley, the tribe’s habitat manager. “Similar work done nearby in 2010 had an immediate effect on the river’s form and function, such as creating deeper pools, gravel bar deposition, and narrowing of the channel.”
Immediately following the 2010 work, steelhead were seen spawning around the logjams. After the first big rainstorm, 43,000 cubic yards of sediment settled and stabilized the jams while creating gravel bars and side channels.
“Over time, this restored channel reach with improving watershed conditions will positively influence the timing, duration and magnitude of river flows and sediment movement downstream in the valley,” Gouley said.
The current work is Phase 2 of a multiphase effort to restore a 12-mile stretch of the river.