Lemhi RM32 Habitat Enhancement Project, Confluence Phase

Project Narrative

The Confluence Phase of the RM32 Habitat Enhancement Project will improve 1 mile of habitat on the Lemhi River and 0.19 miles on Hayden Creek. Hayden Creek is the most productive tributary of the Lemhi River, containing up to 40 percent of the spawning Chinook Salmon in the basin each year along with populations of Steelhead and Bull Trout. This section of the Lemhi River is currently a single channel system with high gradient and little to no rearing and overwintering habitat. This project includes raising riffles in the existing Lemhi River, grading inlets to relic side channels, grading new side channels and floodplains, stabilizing streambanks, and installing instream wood structures which will improve and expand the riparian corridor and create off channel habitat and a side channel network allowing juvenile salmonids the opportunity to stay in the Lemhi basin longer before moving downriver. Native riparian plantings and seedings will be completed to help improve existing riparian habitat and weed management will be conducted to ensure native plants will grow back. The project area will be fenced upon completion to help protect plantings and ensure there is time for the area to recover. The project will also improve the L-40 diversion to reduce maintenance of the existing wing dam and headgate infrastructure and improve operational functionality (action captured under metric fish screen modification). The current L-40 diversion has a wing dam that requires regular in-stream maintenance and repair. The irrigator goes into the Lemhi River two or more times a year to ensure the wing dam is allowing the diversion to function properly. This project will replace the existing headgate with a lateral flow headgate structure that will fully eliminate the need for a wing dam and annual in-stream maintenance. Expanding and enhancing side channel habitat will improve habitat capacity for juvenile Chinook Salmon and steelhead. Reactivating relic side channels and grading new channels will widen the riparian corridor and provide more habitat for fish, while wood structures will add habitat complexity. Constructing riffles in the existing Lemhi River channel will lead to more floodplain activation which will increase the amount of fish habitat and improve the current riparian vegetation. The projects location downstream of spawning grounds on the Lemhi River and Hayden Creek provides an opportunity to provide habitat for rearing parr and overwintering pre-smolts, keeping them in the Lemhi River longer.