The U.S. Army Corps of Engineers (USACE)has broken ground on a five-year, $400 million project to raise the Folsom Dam in California. The higher dam is intended to offer greater flood protection for people living near the Sacramento River, including the state's capital.

The height of the Folsom Dam will be raised in a $400 million, five-year project. Source: USACEThe Corps of Engineers and Bureau of Reclamation dedicated a new auxiliary spillway for Folsom Dam in October 2017 after a $900 million, 10-year effort. That spillway sits 50 ft lower than previously existing structures, offering Reclamation more control over water levels in Folsom Lake and reducing flood risk for the Sacramento region.

Folsom Dam is roughly 23 miles northeast of Sacramento. The project was built by the U.S. Army Corps of Engineers in the 1950s and is operated by the Bureau of Reclamation. Its primary function is flood control, but Folsom Lake stores water for irrigation and domestic use and for electrical power generation.

The main dam consists of a 340 ft high concrete center section flanked by long earthen wing dams extending to high ground at either end. This along with other project features holds more than 1 million acre-feet of water in Folsom Lake.

Project scope

The dam raising project was originally authorized by Congress in 1999, but has changed in scope over the years. It was reauthorized in 2004 and 2007 and the federal cost-share amounts to $373 million. The scope of work that began in mid-January incorporates features designed to take advantage of weather forecast-based decision-making, a process that is expected to enable the Bureau of Reclamation to make more precise water release decisions.

The overall project includes several components:

• A 3.5 ft raise of the Folsom Facility dikes, Mormon Island Auxiliary Dam, Left Wing Dam and Right Wing Dam, along with modifications to the main dam’s Tainter gates.
• Construction of automated temperature control shutters at the main dam to benefit American River fisheries.
• Habitat restoration at two sites along the lower American River.

The taller dikes and dams will raise the surcharge storage capacity of Folsom Lake by 43,000 acre-feet, allowing for more water storage in extreme flood events.

The project is expected to be completed in 2025 and includes funds from state and local sponsors (the Central Valley Flood Protection Board and the Sacramento Area Flood Control Agency) as well as supplemental federal disaster relief appropriations from Fiscal Year 2018.