Clark Canyon Creek Sediment Reduction

The Beaverhead Watershed Committee hired AESI to prepare a detailed preliminary engineering report, feasibility analysis, and cost projection for alternatives to prevent sediment generated in Clark Canyon Creek Watershed from entering the Beaverhead River. Sediment mitigation is a high priority since Clark Canyon Creek flows into a prolific tailwater fishery on the Beaverhead River, and periodic, high sediment loading has had a detrimental effect on the fishery. The large sediment events are typically associated with rain on snow events and are most problematic when the increased sediment delivery from Clark Canyon Creek occurs simultaneously with low flow releases from Clark Canyon Reservoir, thereby causing the sediment loads to exceed transport capacities in the Beaverhead River.

Alternatives analyzed by AESI included releasing flushing flows from the Beaverhead, activating an alluvial fan near the outlet of the North Fork, and constructing a pond to capture the offending sediment. Alternatives were accepted or rejected based on a performed hydrologic analysis, an analysis of the existing landscape, and discussions with parties involved in the project.

The Scope of Work included the following:

• Identification and analysis of highly erosive areas
• Development of alternatives for sediment reduction practices, which involves studying previous work, making field observations and measurements, employing engineering judgment, obtaining limited survey, and completing conceptual designs and costing
• Preparation and submittal of a Technical Report which incorporates preliminary engineering designs, feasibility assessments, and cost estimates for each alternative
• Two meetings with the Beaverhead Watershed Committee Technical Advisory Panel