Auxiliary Spillway Adds to Folsom Dam’s Multi-Purpose Facility

Construction on a new auxiliary spillway at the Folsom Dam is expected to be completed later this year. The auxiliary spillway, which includes a 1,100-foot-long approach channel that will funnel the water from the lake into the spillway, is fitted as a complimentary resource to Folsom Dam’s main functions, allowing water to be released earlier and more safely from Folsom Lake, if needed.

Other auxiliary spillway features, according to the United States Army Corps of Engineers, include: 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.

Folsom Dam is an important part of California’s flood protection system. Due to the abundance of storms in Northern California this year, the floodgates on the dam have been opened periodically to release water from Folsom Lake, allowing storm runoff to safely flow into the lake without flood danger to communities downstream.

Water flowing freely from the Folsom Dam has been a rare sight throughout the state’s historic six-year drought. During that time, water was primarily released because of the consistent demand of supply.

Just as with the drought, those same floodgates are also opened during significant storms, similar to what California has experienced the past month. Due to its small size, the Folsom Reservoir fills quickly and also empties just as fast.

If not for the Folsom Dam, an estimated 700,000 people downstream, along with critical infrastructure, would be in the path of massive flooding.

“The whole purpose of this facility is to avoid downstream flooding,” said Louis Moore, a Deputy Public Affairs Officer with the U.S. Bureau of Reclamation. “Historically, before the dam was in place, all of the storms that came through the area would typically flood the downtown Sacramento area.”

The Folsom Dam, which opened in 1956 and cost $81 million, was built by the Army Corps of Engineers and is 340-feet high and 1,400-feet long.

For more on the Folsom Dam, visit the Bureau of Reclamation here.


Additional resources


Department of Homeland Security

U.S. Army Corps of Engineers

Jonathan Gudel

Jonathan Gudel is a Public Information Officer for the California Governor's Office of Emergency Services (Cal OES). Since joining Cal OES, he has assisted in the response and recovery efforts of the Aliso Canyon Gas Leak, the state's historic drought, the Oroville Dam Emergency Spillway Incident, unprecedented winter storms in 2017, the October (Sonoma County) and December (Santa Barbara County) 2017 wildfires, and statewide wildfire siege in 2018 . Previously, he worked in the newspaper industry for 12 years.

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