S. Fork Asotin Stream Channel Restoration

Washington Department of Fish and Wildlife (WDFW) restored wood and channel heterogeneity to 4 km of lower S. Fork Asotin Cr. on the Asotin Wildlife Management Area in SE WA. This project is the 1st habitat treatment of the Asotin Intensively Monitored Watershed Project (IMW), which began assessment and monitoring in 2008. The goal of the treatment is to restore pool abundance and gravel bar deposition, and increase channel length through the placement of over 200 large wood key piece surrogates for the purpose of increasing production of wild Snake River ESU steelhead. The IMW field assessment identified increased sedimentation, substrate embeddedness, and water temperature, and decreased riparian function, floodplain connectivity, habitat diversity, wood abundance, and pool frequency/quality as limiting factors to salmonid productivity. Based on the limiting factors analyses and further habitat assessments, we concluded that large wood (approximately 200 key pieces) would be required to restore the lower South Fork to reference conditions. The basic design is to drive 3 to 5 posts (<= 4” diameter x 6’ long trimmed to bank full height) into the stream bottom to act as a temporary anchor for racking materials and natural debris recruitment. The use of posts to reduce channel width by 50-75% will help build a more heterogeneous channel shape, increase gravel bar deposition, diversify channel widths/depths, reduce incision, and increase stream channel length. This method has been successful at increasing channel complexity in small tributary streams. This project is intended to benefit steelhead trout.

The goal of the treatment is to restore pool abundance and gravel bar deposition, and increase channel length through the placement of over 200 LWD key piece surrogates for the purpose of increasing production of wild Snake River ESU steelhead.