The state agency tasked with managing the safety of 1,250 dams in California has identified 93 dams that require a “comprehensive assessment” to ensure they can last through next year’s flood season. More than a dozen dams in Southern California are on the list, including Pyramid Dam in Castaic, Cogswell Dam near Devil’s Canyon, and Puddingstone Dam in San Dimas.

After the concrete spillway at the Oroville Dam in the Sacramento Valley crumbled under heavy use earlier this year, the Division of Safety of Dams (DSOD) decided to review more than 100 dam spillways that were considered vulnerable to similar issues because of their capacity, their age (the average dams in California is 70 years old), and the size of the communities they protect.

The DSOD has now released a list of the 93 dams that it concluded need further inspection. Preliminary assessments showed each of the spillways on the list “may have potential geologic, structural or performance issues that could jeopardize its ability to safely pass a flood event,” according to letters the dam-safety division sent to dam owners. The agency has directed dam owners to perform a comprehensive condition assessment of spillways and complete any needed maintenance repairs prior to the next flood season.

The state wants local operators to review each structure’s original design and building materials, its repair history for recurring issues, its drainage system, retaining walls and the geological makeup of its bedrock, among other elements, said Daniel Meyersohn, supervising engineer for the DSOD.

When reservoir levels are high, dam spillways allow the highest volume of water to be released at one time. In Oroville’s case, after heavy rains pushed the reservoir’s water level up to capacity, the dam’s main concrete spillway failed to perform and crumbled, which resulted in more than 100,000 Butte County residents being evacuated.

It was a far worse catastrophe that led to the existence of the Division of Safety of Dams: the failure of the St. Francis Dam in Southern California in 1928. The collapse of the “ill-built” dam created a 70-foot wall of debris that killed more than 450 people, destroyed 900 homes, and laid waste to bridges, roads and farmland. In California’s history, the devastation caused by this event ranks second only to the 1906 San Francisco earthquake. The failure of the St. Francis Dam prompted the State Legislature to create what is today the Division of Safety of Dams, under the California Department of Water Resources.

Source: Los Angeles Times