Sub-Reach 4 Phase 1 Completion; Lower Lemhi Rehabilitation Project

This project will complete Phase 1 of Sub-reach 4 (SR4), Lower Lemhi Rehabilitation Project. The 0.4 mile SR4 is the lowermost section of the 4 sub-reaches that makes up a 2.2 mile contiguous restoration reach in the Lower Lemhi River. Due to the large scale, IDFG partitioned the reach into 4 sub-reaches. Similar to other sub-reaches, SR4 objectives were to address habitat limiting factors and increase capacity to support multiple life stages of ESA listed species. As with most river segments in the lower Lemhi, road development using riprap material was used to stabilize the banks to contain the river and limit its lateral movement into pasture. These techniques have failed on SR4, resulting in flooding to portions of the landowner’s property. IDFG proposed to develop this floodplain footprint into quality fish habitat. SR4 implementation was previously scheduled across two project phases. Both were designed concurrently, with Phase 2 incorporating Phase 1 actions. Phase 1 focused on installing large woody debris structures to provide habitat complexity while addressing the ongoing flooding risk. Construction occurred in 2019, with the idea that a portion of Phase 1 actions would be finalized as Phase 2 was implemented. However, the Phase 2 component has been delayed, thus, IDFG will complete the first phase, while waiting until a more appropriate time to construct Phase 2. Project actions include: 1) removing fill from site and grading fill storage area, 2) improving a temporary road to provide property owners access to areas that were previously available, 3) removing the temporary cofferdam to establish a more functional riparian zone that will offer more sustainable stability to the eroding bank, and 4) installing potted plants and seed.

Sub-Reach 4 Phase 1: Lower Lemhi Rehabilitation Project treatments, completed in 2019, added habitat capacity for the purpose of improving freshwater productivity for Chinook salmon and steelhead in the lower Lemhi River. Phase 1 improved summer parr/rearing and overwinter life stages by deepening the river depth, reducing current velocities, and installing ample large woody debris structures that provide immediate fish habitat while stabilizing eroding banks. The project site was left in construction mode in preparation of the upcoming Phase 2. As Phase 2 has faced a delay, these project actions will complete rehabilitation of the site.