Lower Lemhi Rehabilitation Revegetation

The Idaho Department of Fish and Game (IDFG) will revegetate several phases of Sub-reach 1, the largest sub-reach, of the Lower Lemhi River Rehabilitation Project near Salmon, Idaho. The project area contains 1.25 miles of the Lemhi River, and approximately 4.5 miles of side channels, and is approximately 170 acres in total area. This project aims to revegetate approximately 11.4 miles of streambank (both streambanks will be treated for the Lemhi River and side channels), and 84 acres across four planting zones: the streambank zone, the wetland zone, the riparian zone, and the transitional zone. The zones and corresponding plant communities for each zone are based on root proximity to the water table and frequency of inundation (e.g., 1.5-year flood interval for the wetland zone). The revegetation plan specifies the plant community for each zone and the ideal spacing to maximize recruitment and survival success. Plant species include willows, birches, dogwood, alders, cottonwoods, wild roses, and native berries. Planting will span two years due to the scale of the project and the need to cultivate plants in sufficient quantities to complete planned treatments.



The private landowner provided over 150 acres of previously irrigated production land in the river corridor so floodplain connectivity could be increased. To offset some of the lost acreage, IDFG will purchase a pivot to irrigate a previously flood irrigated field away from the river corridor. There are no water savings or metrics associated with the pivot.

Construction actions on the previous subreaches and phases of the Lower Lemhi Rehabilitation Project addressed many factors limiting productivity and survival of juvenile Chinook Salmon and steelhead. The next and final step is to restore riparian habitats near the

channel and upland habitats in the floodplain with native vegetation plantings. Root systems will solidify and bind the substrate creating natural resiliency, while also allowing for geomorphic processes to continue influencing channel alignment, water velocities, sediment

transport, and point bar formation throughout the project reach. Additionally, vegetation will provide cover for fish and shade the reach reducing predation risk and solar inputs. The combination of floodplain reactivation, side channel complexes, and a healthy riparian zone

will also influence hyporheic flow increasing the interchange between surface and groundwater further mediating water temperatures and retaining water on the project.