Sub-Reach 3 Completion, Lower Lemhi Rehabilitation Project

Project Narrative

This project proposed to complete the remaining implementation actions on the Eagle Valley Ranch Sub-reach 3 (SR3) project that is contained within the 2.2 mile contiguous Lower Lemhi River Rehabilitation Reach. SR3 is one of 4 sub-reaches previously identified in a conceptual design for rehabilitation. Restoration actions were partitioned to most effectively and efficiently address unique challenges found throughout this reach of the Lemhi River. Previous efforts on the rehabilitation reach include and completion of multiple lateral channels and associated floodplain within the downstream half of SR3. The objectives of the Sub-Reach 3 Completion, Lower Lemhi Rehabilitation Project was to complete the entire SR3 section (1.05 miles of stream) by constructing the remaining portions of the lateral habitats and connecting previously constructed channels by restructuring the geometry of the Lemhi River. This included raising the surface water height in key areas so that lateral floodplain areas would be inundated with water. Many of the habitat actions necessary to meet the objective were completed, however, underestimates of earthen fill volumes needing to be removed to activate floodplains resulted in funding shortages. Thus, the Sub-Reach 3 project was split into phases 1 and 2. Phase 1 (0.75 miles of stream) was completed through this project in 2018 and phase 2 (0.3 miles of stream) will be completed in 2019 through PCSRF-funded project 018 18 SA. The project was completed 2 years ahead of schedule because it was split into 2 phases. Project actions completed in phase 1 include:
* Created 0.2 miles of off-channel stream. Created 1.5 acres of off-channel stream. Excavated 10 instream pools. Excavated river banks to reconnect 7.2 acres of floodplain/riparian forest that will allow natural stream channel processes to occur. Installed 30 structures (engineered log jams and other woody debris structures) throughout the existing and newly created stream channels to provide channel structure and roughness. Stabilized 0.07 mile of streambank with revetments. Placed 4,200 cubic yards of spawning gravel in 0.4 mile of stream. Planted 0.05 acres of Salix spp (harvested locally). The purpose of this project is to improve freshwater productivity of the Lemhi Spring/Summer Chinook salmon major population group and the Snake River Lemhi Steelhead distinct population segment, both of which are currently listed as threatened under the ESA. This reach does not effectively support most life stages of salmon and steelhead. It lacks proper stream channel structure and function, instream structural complexity, and proper bed and channel form. Sediment quantity is poor, in that, large homogenous substrate unsuitable for salmonid spawning dominates the reach. Water velocities are very high, and there are no slow water or lateral habitats suitable for fish rearing and growth. There is a substantial loss of riparian vegetation, and the existing condition is poor. Stream temperatures are elevated during summer periods, in part due to loss of riparian vegetation within and upstream of the proposed reach. Project actions will improve all of these identified issues.