The Folsom Dam Auxiliary Spillway project is an approximately $900-million cooperative effort between the U.S. Army Corps of Engineers and the U.S. Department of the Interior, Bureau of Reclamation that will help the Sacramento region achieve 200-year level of protection, meaning there will be a one-in-200 chance for flooding in any given year.
The project will construct an auxiliary spillway to compliment the functions of the main Folsom Dam. It will allow water to be released earlier and more safely from Folsom Lake during a high water event.
The spillway will include an 1,100-foot-long approach channel that will funnel the water from the lake into the spillway; a control structure with six submerged gates that will be controlled in coordination with the gates on the main dam to control water releases; a 3,027-foot-long spillway chute that transports the water from the control structure to the American River below; and a stilling basin that will slow the racing water back to normal flow levels that the river channel will be able to withstand. The entire spillway structure will operate in conjunction with the existing operations of the Folsom Dam and is not intended to replace any of the dam’s current functions or increase the height of the reservoir.
The level of cooperation between the Corps of Engineers and the Bureau of Reclamation on the auxiliary spillway is extraordinary. The Reclamation has responsibility for dam safety as well as operation and maintenance of the Folsom Dam facility, while the Corps of Engineers is responsible for flood damage reduction. By combining their efforts into a single project, the two Federal agencies will complete the project faster and at a lower cost.
The auxiliary spillway is scheduled to be completed in late 2017.