American River Watershed Folsom Dam Modifications and American River Watershed Folsom Dam Raise
Completed in the mid-1950’s, Folsom Dam is the cornerstone of Sacramento’s flood control system on the American River. Considering larger flood events that occurred after its completion, it was recognized in the late 1980s that improvements to Folsom Dam and Reservoir, combined with improvements to downstream levees, were necessary in order to provide what flood control officials deemed a minimum 200-year level of flood protection to the Sacramento area.
A new dam and auxiliary spillway, called the “Joint Federal Project” or “JFP” (because the U.S. Army Corps of Engineers (USACE) and U.S. Bureau of Reclamation each constructed a portion of the project), was completed in 2017. The new spillway was constructed adjacent to Folsom’s main concrete dam and includes a 1,100-foot-long approach channel beginning in Folsom Reservoir with submerged gates embedded in a new control structure designed to discharge water down a 3,100-foot-long spillway chute. Because the auxiliary spillway’s gates are lower than those at the main Folsom Dam, dam operators are able to quickly create more available flood storage space in the reservoir in anticipation of increased inflows during storm events.
To further increase flood control space in the reservoir, the USACE is raising the existing main dam and reservoir’s surrounding dikes by 3.5 feet, which began in 2019.