The Hamilton Branch Diversion Dam located in Lassen County, California, diverts water from the Hamilton Branch of the Feather River into a canal, which conveys water for the Hamilton Branch Powerhouse.
Originally built in 1924 by the Red River Lumber Company, the existing timber crib and rock fill dam, which is approximately 90 feet long and 18 feet tall, has deteriorated and seepage has been observed through the left and right abutments. SAGE performed a geologic reconnaissance, condition assessment, and an alternatives analysis to evaluate the various rehabilitation and replacement alternatives, and a feasibility study of each option while reducing the potential for seepage, minimizing construction cost, improving the service life of the dam, and increasing the survivability during high floods.
SAGE designed an alternative to address the deteriorating timber crib abutments and seepage problems without a complete dam removal. This alternative allowed the client the flexibility to implement a less intensive project now, by only replacing the abutments, and the opportunity to replace the main superstructure at a later date if further deterioration occurs.
The results of the alternatives analysis led to the design of new concrete abutments on both ends of the dam, while leaving the existing main timber superstructure in place. Only minor repairs to the superstructure were proposed. Design included a geotechnical investigation and structural design of new concrete abutments, including tie-ins to the existing structure. Design was consistent with ACI-350, ACI-207, and the USBR Design of Small Dams.
Other services provided by SAGE included:
- Preparing construction cost estimates for feasible alternatives;
- Preparing conceptual figures of each alternative;
- Performing preliminary spillway sizing for dam replacement alternatives;
- Preparing a final report presenting each of the evaluated options; and
- Preparing construction documents for the client-selected alternative.