L3AO-L3 Lemhi Reference Reach Restoration Plan
This project was developed as a reach-scale restoration effort for the lower Lemhi River from approximately river mile 3.2 to 4.8. Rio ASE collaborated with multiple partners to identify conceptual habitat improvement actions to be implemented in the reach while supporting existing land and river reach uses. The resulting Strategic Restoration Plan describes reach-scale geomorphic conditions and processes that influence the existing and future channel dynamics and fish habitat availability. This information was used to inform the development of restoration concepts to address altered functional processes and improve ecological conditions and fish habitat, all of which was summarized in a Restoration Plan that also depicts hydrology and hydraulic modeling results supporting recommended restoration actions.
Oblique view of the L3AO-L3 Lemhi Reference Reach.
Following the Restoration Plan, Rio ASE developed conceptual designs for the project reach with the objective of enhancing floodplain connectivity, secondary channel formation, and diverse in-stream and off-channel habitat in a “Stage-0” channel evolution setting. The design utilizes detailed 3D surface topology generated from combined LiDAR and ground survey. The existing grade was used to develop a robust 2D hydraulic model of the existing project area. Additionally, Rio ASE performed geotechnical investigations to understand groundwater interactions and depth to gravel in the floodplain. These analyses were collectively used to assist in design development and risk evaluation.
Example restoration concept.
Example shear stress model results.