Middle Lemhi River – Hayden Reach Phase 1

The Lemhi Soil and Water Conservation District (LSWCD) will design and construct habitat treatments on a 0.30 mile segment of the Lemhi River located near the confluence of Hayden Creek and the Lemhi River. Current habitat conditions include a straightened channelized river segment confined by State Highway 28 that contains no instream woody structure, no side channels or other lateral habitat, a disengaged floodplain, and limited riparian vegetation.



The project goal is to increase habitat capacity for juvenile salmon and steelhead by improving the current degraded condition. Project actions prescribed to meet these objectives include: 1) construct a new alignment for the Lemhi River (including pool excavation) to increase sinuosity, 2) grade existing river banks and raise the surface water elevation of the river by installing engineered riffles (unanchored boulders) to improve river and floodplain function, 3) install engineered log jams, bank roughening structures, and other woody debris structures (anchored and unanchored logs, rootwads) throughout the re-aligned river and newly created stream channels to provide channel structure, roughness, and complexity, 4) execute floodplain grading surrounding new channel alignment to increase lateral floodplain connectivity, 5) streambank stabilization through use of logs, revetments and vegetation, 6) grass seeding and plantings of native herbaceous and woody species to rehabilitate the riparian zone.



This is Phase 1 of a 2-Phase project that will focus on habitat rehabilitation along approximately 0.70 miles of the Lemhi River. Phase 1 will be implemented under this contract, with treatments constructed along 0.30 miles of the Lemhi River. Phase 2 will be designed concurrently, with funding pursued in the fall of 2021 and implementation scheduled for 2022 and 2023.

Developing a large portion of this property into more of a natural floodplain while restoring natural river processes and function will directly increase habitat capacity for juvenile life stages of salmon and steelhead. Improving the current condition by increasing river sinuosity, developing habitat complexity in the form of woody debris structures, constructing side channels, and riparian zone restoration will result in improved survival for all freshwater juvenile life stages. Furthermore, the magnitude of these affects will be substantial since project is located at the downstream end of the Lemhi primary Chinook salmon production area. Immediately upstream of the project site, the Lemhi River is a heavily incised single thread channel with no functional summer rearing or wintering habitat. As such, the project is ideally located to function as a “catcher’s mitt”, providing much needed habitat for rearing parr that were displaced by spring high flows from upstream production areas, and for pre-smolts moving out of the production areas in the fall in preparation for overwintering. The conceptual design directly addresses these life stages by developing instream habitat and floodplain diversity.