Davis Irrigation Dam Fish Passage

The Davis Dam is a 6-foot tall reinforced concrete structure that spans the entire width of the Musselshell River. The concrete weir spans 120 feet across the river with sloping concrete ends tying into the adjacent ground. The dam consists of an earthen core capped by reinforced concrete. A riprap pad is positioned at the base of the dam. The dam has been in place since at least 1938 and has since impeded the passage of fish, namely sauger and channel catfish.

AESI in collaboration with ERM completed an alternatives analysis to explore the feasibility of several potential alternatives for retrofitting Davis Dam to provide fish passage for sauger and other species and to extend the functional life of the concrete structure. Several alternatives were developed and vetted. A coarse screen was used to evaluate each of these alternatives against the design criteria established by the consultant team and FWP. The following two alternatives were selected for further and more detailed analysis: Remove Dam and Establish Pump Station and Fish Passage Right of Structure. Conceptual analysis, design and costs were developed for each of these two feasible alternatives and were summarized in an alternatives report.

The scope of work included:

• Topographic survey
• Site reconnaissance and geotechnical evaluation
• Structure stability evaluation
• Analysis of fate and transport of impounded sediments under dam removal alternative
• Development of design criteria
• Development and analysis of feasible alternatives and cost estimates
• Preparation of an alternatives analysis report