Projects

Eighteenmile Creek Ellsworth Habitat Improvement Project

In 2020, Rio ASE and Intermountain Aquatics teamed to work with the Lemhi Soil and Water Conservation District on a rehabilitation effort on Eighteenmile Creek in the Lemhi River watershed. Historically a major anadromous fish producer, Eighteenmile Creek had been disconnected intermittently by irrigation practices and streamflow variations. After a successful project in 2019 on an upstream portion of the creek, the LSWCD proposed the Ellsworth project with the goals of improving water quality through stream bank stabilization and reducing sediment delivery to the creek; establishing a weed-free, native riparian community to increase shade and prevent increases in water temperature; and improving instream habitat by mitigating anthropogenic effects to increase instream habitat.

Constructed in summer 2021, the project featured small woody habitat structures, beaver dam analogues, and willow rootballs to promote hydraulic diversity, sorting of sediments, and improved floodplain connectivity. New channel segments were excavated and portions of the existing channel were partially filled to improve the width-to-depth ratio, allowing for more natural channel processes to occur. Increased floodplain connection also created greater storage capacity for fine sediments, resulting in an improvement in overall water quality. Rio ASE’s design increased sinuosity in the project reach by 50% and fill material from the newly excavated channel and floodplain was used to develop vegetated floodplains. Intermountain Aquatics developed a planting plan that featured native species planted in the riparian zone as well as transplanting local vegetation harvested near the project site.