Big Springs Lemhi River Confluence Restoration Project P2

Project Narrative

Phase II of the Big Springs Lemhi River Confluence Restoration Project improved 1850 of existing Lemhi River channel, as well as 4700 in Big Springs (1.24 mile total) through channel reconfiguration. Twenty pools were added, and 4.3 acres of floodplain were re-connected. Large wood structures were placed throughout the reach and 15 pools are expected to be created through scour. Riparian planting occurred on 2.48 miles of streambank and 0.6 mile of fence was installed to protect 3.4 acres. One water gap was installed. Riparian exclusion was erroneously reported in the proposed metrics and was double-counted with the fence. During project development, the landowner requested a water gap; it was not in the proposed metrics. The 170 proposed structures to be placed in channel were over-reported as individual large wood pieces in the proposed metrics. The final metrics report the number of structures installed, which each consist of numerous large wood pieces. The project will improve habitat for ESA-listed spring Chinook Salmon (Oncorhynchus schawytscha), summer steelhead (Oncorhynchus mykiss), and bull trout (Salvelinus confluentus). Project goals are to improve habitat for limiting life stages of ESA-listed fish, restore natural channel processes to maintain diverse habitat, and to address shade targets set in the Conservation Easement.The project aims to maximize short-term and long-term riparian and shade conditions to address established shade targets, reduce the channel width to a more appropriate geometry, increase in-stream hydraulic diversity and velocity gradients, increase pool size and frequency, increase interstitial space along margins, and increase in-stream cover. The design will increase sinuosity and add multi-threaded channel segments, narrow over-widened areas, and add in-stream structure to improve fish habitat and floodplain connectivity; excavate pools and create constrictions and place structure allowing the channel to maintain pools and a narrower, deeper channel while enabling a variable channel geometry; utilize existing mature riparian vegetation where feasible and appropriate to create immediate increases in bank structure, riparian conditions, and shade; and plant willows and sedges to enhance riparian conditions over time.