Projects

Lemhi River Eagle Valley Ranch Subreaches 1, 3, and 4

In 2017, Rio ASE began working with the Idaho Department of Fish and Game (IDFG) on their restoration strategy for the Eagle Valley Ranch property along the Lemhi River near Salmon, Idaho. Work has progressed from adjacent side channel projects to full-scale channel relocation and reconstruction spanning two miles of river and three subreaches. As the project scale grew, the U.S. Bureau of Reclamation (USBR) took over design funding and contracting for Rio ASE, while still coordinating with IDFG. The primary goal of the multi-phase project is to provide rearing and refugia habitat to juvenile spring Chinook salmon, steelhead, and bull trout by restoring natural or historical channel forms and processes. Secondary project goals include increasing floodplain connectivity while minimizing risk to private infrastructure and property from flooding and erosion.

2D hydraulic model output show the depth of proposed conditions in Subreach 1 at the 25-year design flow. This channel’s planform is an anabranching, multi-channel network to increase complexity and available habitat for juvenile salmonids.

Constructed from 2018 to 2019, Subreach 3 includes approximately 1 mile of new perennial side channel, 0.8 miles of improved habitat in the mainstem Lemhi River, 31 new engineered log jam (ELJ) structures, and 8 mainstem constructed riffles. Subreach 4, constructed in 2019, includes an excavated alcove and levee setback to stabilize around 150 linear feet of eroded streambank by recontouring the bank and incorporating 9 ELJ structures. Subreach 1 includes floodplain grading, relocation of irrigation diversions, approximately 2 miles of mainstem channel realignment, 3 miles of new side channel, and over 150 ELJ structures. Subreach 1 is the largest and most aggressive design, with construction completed over a four-year period due to its scale. Subreach 1 Phases 1, 2, and 3 have been constructed as of September 2024; Subreach 1 Phase 4 is scheduled for construction in 2025, representing the final phase of construction for this project.

Tasks performed by Rio ASE include completing conceptual to final designs (plans, specifications, and cost estimates), stakeholder outreach and presentations (Idaho Transportation Department and Lemhi County), 2D hydraulic modeling, aquatic habitat suitability modeling, permitting support, bid support, and construction observation.