Big Springs Lemhi Confluence Restoration Project
Big Springs Creek is a spring-fed channel tributary of the Lemhi River that collects groundwater and minor surface water from the south. This project is located on approximately 3,600 feet of Big Springs Creek and 3,000 feet of the Lemhi River at their confluence near river mile 52.7. Rio ASE began with a geomorphic assessment that evaluated channel evolution, character, and the potential for improved riparian and fisheries habitat. Then, we identified the systemic cause-and-effect relationships and developed recommendations to improve the physical habitat of the project area. Recommendations were prioritized based on tiers of habitat conditions on a scale ranging from Functioning to Impaired to Recovering. Rio ASE worked with the Lemhi River Land Trust and other project partners to identify and develop three priority project phases within the assessment area: Fayle, Big Springs, and Confluence. We managed the design team and participated at the lead geomorphologist and lead design engineer for all three.
The goal of each phase included improving in-stream and off-channel habitat for threatened Chinook salmon and steelhead by restoring the appropriate channel form and improving natural channel processes. Rio ASE provided geomorphic and engineering design services (including hydrology, hydraulics, stream design, riparian planting zones, and engineered log jam design) from conceptual through final design. The projects all relocated the channels to existing areas of robust riparian vegetation, increased channel sinuosity, narrowed the channel width, increased flow depth, placed in-stream structure (woody debris), created channel constrictions to form and maintain pools, increased velocity variability, reconnected the floodplain, and established a robust riparian community.
Video taken in 2017 showing construction being completed on the project.
Two project areas, Fayle (Phase I) and Big Springs (Phase II), were constructed in 2017; construction on Confluence (Phase III) was completed in 2019. Rio ASE is continuing to coordinate with the Lemhi River Land Trust to identify and develop several additional projects within the overall assessment area. In addition, Rio ASE developed and initiated a 5-year monitoring plan to evaluate project effectiveness.
Big Springs Creek in 2017, prior to project construction.
Big Springs Creek in 2019, six month after construction completed.
Aerial oblique of Big Springs Creek taken in summer 2022, showing various treatments incorporated into constructed design.