Renner Reservoir Dam Repair and Outlet Works Rehabilitation
Trihydro worked for the Wyoming Game and Fish Department to restore the Renner Reservoir, a once popular fishery, through an extensive rehabilitation design project encompassing a UAS topographic survey, a plan to repair a breach, construction management and oversight, and more.
Trihydro worked for the Wyoming Game and Fish Department (WGFD) to restore the Renner Reservoir in Big Horn County, Wyoming. The once popular fishery was experiencing decreased game fish numbers. In July 2016, WGFD breached the embankment to drain the 367-acre-foot reservoir and flush a stunted sunfish population. This also allowed for repairs to the outlet works and the removal of accumulated sediment to increase water depth and improve habitat.
The WGFD contracted Trihydro to undertake several tasks to restore the reservoir, including:
- Undertake a UAS topographic survey
- Evaluate the basin upstream of the reservoir
- Design new outlet works that, when combined with the spillway, could pass the 100-year storm event
- Develop a plan to repair the breach
- Abandon a water supply pipe through the embankment
- Improve the fish habitat and increase the reservoir depth
- Provide construction management and oversight
Repairing the Breach
To repair the breach, our team completed geotechnical investigations to identify a borrow source and analyze the existing structure’s stability. With limited data, the original investigation concluded that there were unacceptably low margins against failure that would require redesign or reconstruction of the entire dam. A second investigation was completed that included additional borings and site visits to better understand the foundation, material strength, and seepage observed downstream. With this additional data, the Wyoming State Engineer’s Office approved an acceptable safety margin for embankment repair.
Safety Requirements
Because the reservoir capacity is over 50 acre feet, the dam falls under the Wyoming State Engineers Safety of Dams Statutes §41-3-307 to 41-3-317. To meet the Safety of Dams requirements, Trihydro developed a design report and produced plans and specifications to stabilize the embankment and reconstruct the dam breach. The design report summarized the geotechnical analysis, confirmed the dam hazard classification, updated the hydrology, and outlined the design of the dam breach repair and outlet works to meet Safety of Dams requirements. We also enlarged the auxiliary spillway to meet present-day engineering standards.
Construction Services
Working with the WGFD Statewide Habitat and Access crew, Trihydro provided construction survey staking, observation, and daily reporting to the WGFD project manager and Safety of Dams.
Challenging foundation conditions that required field engineering were encountered during construction. The project, however, was completed successfully and on time. The reservoir was re-filled, stocked with fish, and is now being enjoyed by the public once again.
