Folsom Lake is a large reservoir created by the construction of the Folsom Dam, located in Northern California, northeast of Sacramento. It serves as a major water storage and management facility for the region and is a primary component of the federal Central Valley Project, which manages California’s water resources. The reservoir transformed the landscape, turning a river canyon into an expansive lake with approximately 75 miles of shoreline when full.
The Folsom Dam Construction
The Folsom Dam project was authorized in 1949, began construction in 1951, and was completed in 1955, officially opening in 1956. The U.S. Army Corps of Engineers led the construction before transferring operations to the U.S. Bureau of Reclamation.
The structure is primarily a concrete gravity dam, measuring 340 feet high and 1,400 feet long across the American River gorge. This concrete section is supported and extended by approximately nine miles of earth-fill wing dams and dikes that connect the main structure to the high ground. The construction was a complex engineering feat that faced challenges, including multiple washouts of temporary cofferdams due to high water.
Primary Purposes of the Reservoir
The project’s primary purpose was to provide flood control for the Sacramento metropolitan area. The dam manages seasonal runoff from the Sierra Nevada mountains, preventing billions of dollars in potential flood damage to downstream urban and agricultural areas.
The reservoir is also a significant source for water supply, providing water for irrigation, municipal, and industrial uses. Folsom Lake is designed to hold a total capacity of approximately 977,000 acre-feet of water, stored during wet periods for use during drier months and years. The facility also includes the Folsom Powerplant, which generates hydroelectric power for the regional grid.
The management of Folsom Lake requires balancing these competing demands, such as maintaining space for flood storage while conserving water for power generation and domestic use. Operations must also regulate water temperatures in the Lower American River to support anadromous fish species like Chinook salmon.
Geographical Context and Water Source
Folsom Lake is situated in the Sierra Nevada foothills, roughly 25 miles northeast of Sacramento, spanning parts of Sacramento, Placer, and El Dorado counties. The reservoir was formed at the confluence of the North and South forks of the American River.
The lake’s surface area covers approximately 11,500 acres when at its maximum operating elevation. Water levels fluctuate significantly throughout the year, driven by the need to manage flood capacity and meet downstream water delivery schedules.