Santiago Creek Dam improvement project

The Santiago Creek Dam forms Irvine Lake, which since 1933, has served as a vital part of Orange County’s water infrastructure. While Irvine Lake provides recreational benefits to the county, its primary purpose is to store water for the benefit of surrounding communities. Irvine Lake is an important source of water for the Baker and Howiler treatment plants, which collectively provide water to 85,000 homes in Central and Southern Orange County.

Beginning in 2017, IRWD undertook a comprehensive assessment of the 90-year-old Santiago Creek Dam. The assessment determined that the engineered earthen embankment dam is still operational but could be made safer, and that the outlet tower and spillway are reaching the end of their useful life and need to be replaced and upgraded to today’s seismic and safety standards. The project will reconstruct the spillway and outlet tower, restore storage capacity in the reservoir, and strengthen the dam to meet today’s modern standards. The project is being designed using a Risk Informed Decision Making (RIDM) process that uses a rigorous, systematic, and thorough approach to dam safety that identifies and reduces risks. Incorporating RIDM into the project design goes above and beyond current standards required by the state and will result in a safer facility that will increase water reliability for decades to come.

Replace the existing outlet tower that controls flow into and out of the reservoir, improve the regulation of flow, and bolster the seismic performance of the structure. The new outlet tower will be embedded in bedrock within the slope and include multiple intakes, creating increased efficiency and seismic stability.

Construct a new and safer spillway structure. Improvements will meet today’s seismic safety standards.

Strengthen the earthen embankment dam. Upgrade will further enhance safety.

Preserves and restores local water supplies — The project will significantly enhance local water availability by restoring the reservoir to its original storage capacity. This will allow for more local rainwater capture and reduce the need to buy expensive, untreated imported water. Increases water resiliency – The improvements will restore the lake’s current capacity, adding 3,700 acre-feet of water. This will result in enhanced water resiliency and reduce dependence on imported water. Increases safety and reliability – The dam safety improvements, exceeding the requirements set by Division of Safety of Dams guidelines, will result in increased reliability long into the future. Improves efficiency and seismic performance – The new outlet tower will better control flow out of the reservoir and be designed for optimum seismic performance. Promotes the well-being and security of the communities we serve. More than 1.5 million residents live in areas impacted, directly and indirectly, by the Santiago Creek Dam. The project’s modern safety upgrades will further protect residences, businesses, essential services, and critical fire/life safety infrastructure.