Improve the ability to manage large flood events by allowing more water to be safely released earlier in a storm event and leaving more storage capacity in the reservoir to hold back the peak inflow when it arrives. A peak inflow of 450,000 cubic feet per second in a 200-year design storm, releases can be held to 160,000 cubic feet per second or less, which can be safely conveyed with the improved American River levees. The new auxiliary spillway also allows passage of the probable Maximum Flood (PMF) without damaging the dam.
This project consists of a six-gated control structure, a 2100-foot spillway with a stilling basin, and an approach channel in the reservoir leading to the control structure.
Phase 1 spillway excavation began in January of 2008 and is now complete. Phase 2 work, led by the Bureau of Reclamation, was awarded in Spring of 2009 for $64.0 million. Phase 2 work consists of excavating out the spillway downstream of the proposed gated structure. The work is expected to be complete in the Fall of 2010 and can be seen by taking the new Folsom Dam Road.
The next phase of work (Phase 3) is the gated control structure. The Corps of Engineers is expected to award this contract in Fall of 2010. Work is expected to be completed in 2015.