Santiago Creek Dam Improvement Project
Increasing water resiliency, enhancing safety, and improving efficiency
HISTORY OF THE DAM AND IRVINE LAKE
• Originally constructed in 1933, the Santiago Creek Dam forms Irvine Lake, which serves 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 900,000 people throughout Central and Southern Orange County.
PROJECT OVERVIEW
Beginning in 2017, Irvine Ranch Water District 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. We also found 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.
Interested in learning more about dam safety? Watch the IRWD video: English | 中文字幕 | 한국어 자막
THE DETAILS
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. View video: The importance of safety.
Strengthen the earthen embankment dam.
• Upgrade will further enhance safety.
TIMELINE
BENEFITS
- Preserving and restoring 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.
- Increased 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.
- Increased 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.
- Improved 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 for 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.
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QUESTIONS?
Send an email to info@IRWD.com
DOCUMENTATION
Scoping Meeting presentation and flier (May 16, 2023)
Notice of Preparation and Scoping Meeting (May 16, 2023)
Draft EIR documentation will be available on IRWD.com on Monday, April 28, 2025.
ENVIRONMENTAL IMPACT REPORT
View video: The importance of environmental stewardship
Draft EIR – Executive Summary (April 2025)
Draft EIR – Notice of Availability (April 2025)
- Note: IRWD provided a copy of the Draft EIR to Heritage Park Library for public review. However, this library will be temporarily closed from May 16 to August 4 as library management transitions from the County of Orange to the City of Irvine. To view a hard copy of the Draft EIR after May 15, please visit one of the two other locations noted in the Notice of Availability (IRWD’s Sand Canyon office or Library of the Canyons).
Draft EIR – Full Document (April 2025)
- Draft EIR Appendix A – Notice of Preparation and Comment Letters
- Draft EIR Appendix B – Air Quality and Greenhouse Gas Emissions Technical Memorandum
- Draft EIR Appendix C – Biological Technical Report
- Draft EIR Appendix D – Historic Property Identification Report and Paleontological Resources
- Draft EIR Appendix E – Energy Calculations
- Draft EIR Appendix F – EDR Radius Map
- Draft EIR Appendix G – Noise and Vibration Technical Memorandum
