Wave of Construction Kicks Off at Folsom Dam

In early 2020, while the rest of the Sacramento region headed to their homes to ride out the COVID-19 pandemic, a long line of construction equipment under contract by the U.S. Army Corps of Engineers Sacramento District was instead heading to the jobsite.

The first of eight dikes bolstering the west and south shores of Folsom Lake, Dike 8, gradually rose three and a half feet at the southern tip of the lake. Contracted workers donned safety vests, boots, and something new—the face mask—while work continued on Dike 8.

An aerial image shows completed construction on Dike 8, part of the Folsom Dam Raise Project, Folsom, Calif., July 2, 2020. Contractors with the U.S. Army Corps of Engineers Sacramento District raised the dike 3.5 feet to increase the surcharge storage capacity in Folsom Lake, reducing flood risk for the Sacramento area. USACE PHOTO BY SACRAMENTO DISTRICT AVIATION SECTION

“Weather doesn’t take off days,” said Gerry Slattery, Folsom Dam Raise program manager with the Sacramento District. “We realized we could ensure worker safety while continuing to advance this key piece of flood infrastructure. So that’s what we did.”

Folsom Dam is not just one structure; it’s made up of a main dam, two wing dams (left and right), the Mormon Island Auxiliary Dam, and the eight dikes. Dike 8 was the first of all this infrastructure to be raised 3.5 feet, but far from the last. All of these components are scheduled to undergo a similar raise by 2028.

And before the dike work, there was the emergency spillway—a joint federal project spearheaded by the Bureau of Reclamation as well as USACE.

“This work builds on the success of the Joint Federal Project by allowing larger flood events to be managed without overtopping downstream levees,” said Slattery.

The Sacramento Area Flood Control Agency and the California Department of Water Resources (SAFCA and DWR) are project partners that provide a portion of the construction funds. Reclamation owns and operates the dam.

Working together, USACE and Reclamation have conducted extensive quantitative risk analyses on the dam raise designs to ensure the finished product enhances dam safety and that construction operations do not temporarily render the dam unsafe.

An aerial image shows completed construction on Dike 8, part of the Folsom Dam Raise Project, Folsom, Calif., July 2, 2020. USACE PHOTO BY SACRAMENTO DISTRICT AVIATION SECTION

“After USACE’s improvements are complete, we will conduct a post-construction analysis with Reclamation to ensure risk management objectives have been met,” said Slattery. “This is standard procedure for all USACE projects, and can sometimes continue for years after project completion.”

And during the three-year gap between Dike 8’s construction and the recent contract awards, analysis and redesign was exactly what USACE was doing. Each dike is unique and must be designed to exact specifications based on the terrain and expected hydrologic behavior during a flood event.

“The design process for the remaining dikes was underway when we finished Dike 8,” said Slattery. “We applied the lessons we learned in 2020 to the other earthen structures.”

“It took a little more time, but we ended up substantially reducing projected construction costs,” he added.

The final contract on the Folsom Dam Raise project (for Dike 7) will be awarded in 2024, and construction under all contracts is expected to be complete in 2028.

For updates on Folsom Dam Raise construction, bookmark the project’s webpage at https://www.spk.usace.army.mil/Missions/Civil-Works/Folsom-Dam-Raise/.