Major Retrofit to Perris Dam Completed, Reduces Seismic Risks

By on April 28, 2018
Department of Water Resources

The California Department of Water Resources (DWR) has announced the completion of major retrofit to Riverside County’s Perris Dam. The recently completed work will reduce seismic risk to the dam which was originally constructed from 1970 to 1973.

“DWR used state-of-the-art engineering techniques to modernize this dam as part of our ongoing effort to upgrade California’s aging infrastructure, especially its network of dams,” said Karla Nemeth, DWR Director. “Our safety engineers continuously monitor our dams to identify any potential future problems. We’re committed to making the necessary investments to upgrade our infrastructure to protect our water system and enhance public safety.”

The remediation of Perris Dam is one of three major seismic stability and enhanced public safety projects that comprise the Perris Dam Remediation Program (PDRP). The program’s Outlet Tower Improvements, scheduled for completion in 2021 and the Emergency Release Facility (ERF) Project, with completion planned for 2022, comprised the remainder of the PDRP.

The ERF project provides improvements downstream of the reservoir that would direct the flow of water in an emergency requiring the dewatering of the reservoir. Flows would be directed through a series of berms and lined and unlined channels that would ultimately terminate at the Riverside County Flood Control and Water Conservation District’s Perris Valley Channel. Lake Perris is the State Water Project’s southernmost facility and the terminal storage facility on the East Branch.

California’s sporadic earthquakes pose some of the greatest risks to the state’s more than 1,400 dams with more than 50 of them capable of holding 100,00 acre-feet or more of water. In the late 1990s DWR’s Division of Safety of Dams (DSOD) began conducting in-depth investigations and re-evaluations of dams located near seismic faults. Since then, California’s dam owners have spent some $1.5 billion on seismic improvements to dams.

Seismic retrofits to Perris Dam began in 2005 after it was identified as a high priority state-owned dam due to its proximity to nearby faults and large downstream communities. The seismic retrofit to Perris Dam began in 2005 and have been designed to withstand a magnitude 7.5 earthquake.

At the start of the project DSOD ordered the Lake Perris water level to be lowered to 25 feet to ensure public safety while the state identified the seismic risk and developed a plan to address the dam’s seismic stability deficiencies. The dam retrofit has included strengthening roughly 800,000 cubic yards of 130-foot tall, earthen dam’s foundational material by mixing cement with soil and reinforcing it with a 1.4 million-cubic-yard earthen stability berm placed on the downstream side of the dam.

The Perris Dam’s completion – along with the approvals from an Independent Consulting Board of recognized dam safety experts and DSOD – have allowed the DWR to begin refilling of the dam’s reservoir. A controlled refilling of the reservoir began in early March and, depending on rainfall and DWR operations, the reservoir will likely resume normal operational capacity by the end of the year.

When the Perris Dam remediation began in fall of 2014, public access to the southeast side of the Lake Perris State Recreation Area was closed. DWR has indicated that access to hiking trails, undeveloped campsites, and rock climbing will be opening soon.