Completed in 1955, the dam, located on the American river, is a 103.6m high concrete structure flanked by earth wing dams and dikes, and impounds 1.25Bm3 of water. The power plant has three generators providing 198.7MW of electrical power.
The new project proposed by the US Army Corps of Engineers (USACE) requires modifications to the dam including raising the height to enhance flood protection.
In February 1986 major storms in northern California caused record flood flows in the American river basin. Outflows from Folsom reservoir, together with high flows in the Sacramento river, caused water levels to rise above the safety margin on levees protecting the Sacramento area, northern California. The 1986 floods raised concerns over the adequacy of the existing flood control system, and led to a series of investigations into the need to provide additional protection to Sacramento.
The proposed action consists of enlarging the eight existing river outlets, constructing two additional river outlets and modifying the use of surcharge storage at Folsom. Construction of the outlet modification component would increase flood protection by reducing the probability of flooding in Sacramento in any one year from 1-in-100 to 1-in-130. Construction of the surcharge component would increase flood protection to Sacramento by reducing the probability of flooding from 1-130, to 1-140 in any one year.
Once the Folsom modification project is complete, USACE would revise the water control manual for Folsom dam to reflect the new flood control diagram. The US Bureau of Reclamation would continue to operate the dam in accordance with the revised water control diagram.