Upper Castaic Lake closed today due to an elevated danger algal bloom advisory.
Castaic Dam Modernization Program
Castaic Dam in Los Angeles County is a State Water Project facility that began a modernization program in 2018.
Castaic Dam, Lake, and Lagoon are located 45 miles northwest of Los Angeles and provide water for the greater LA area. Castaic Lake supplied water to more than 4.8 million Californians in 2021. The dam was built between 1965 and 1974 as part of the California Department of Water Resources' State Water Project (SWP).
DWR is modernizing its SWP facilities across the state, including Castaic Dam. This consists of identifying and proactively addressing any issues that could impact the delivery of water or the safety of surrounding communities. In fall of 2019, DWR initiated field work for the Castaic Dam Modernization Program. Over the next several years, DWR will conduct assessments of the dam and associated structures, and undertake construction activities to ensure the dam continues to function safely.
Status of Dam
The California Division of Safety of Dams (DSOD) rated Castaic Dam as poor – meaning there are deficiencies that require remedial action. The Condition Assessment rating is an expected result of the issues that DWR’s Division of Operations and Maintenance is already evaluating, investigating, and addressing through the Castaic Dam Modernization Program. The issues include the performance of the spillway during an extreme flood event, and the performance of the intake towers during a major earthquake. Based on DWR’s latest evaluations, the dam itself is safe for continued operations. The timeline below provides additional details on DWR’s progress in resolving these issues.
Castaic Dam Modernization Components
Castaic Dam and Lake Statistics
Dam Lake
Height: 425 feet Storage Volume: 323,700 acre-feet or 105.5 billion gallons
Length: 4,900 feet Surface Area: 2,240 acres
To view Castaic Lake water storage during this project, see weekly reservoir storage chart for Castaic Lake.
Spillway Condition and Extreme Weather Assessments
- Dam safety engineers continue to monitor the concrete wall and floor panels in the spillway for movements caused by the underlying expansive bedrock. Instrumentation installed in the spillway in 2021 have been beneficial in understanding the current rate of movement, which is very slow. As the data collected over the years is showing undesirable cumulative wall displacements in some locations, interim, short-term measures to protect select wall panels are being considered and may be implemented in advance of a larger rehabilitation effort for the spillway.
- Over the years, DWR has carefully and consistently managed the reservoir’s water levels so that the spillway would not be activated due to these shifted concrete panels. In fact, the spillway has never spilled. Inspection and maintenance are also performed on an annual basis. Climate models show that increased temperatures in California will result in more precipitation falling as rain rather than snow, which will alter river flows throughout the state and result in the potential for even larger extreme events. DWR is taking these weather pattern uncertainties and potentially larger inflows into account as alternatives for the spillway’s rehabilitation are evaluated.
Safety Assessment
A Safety Assessment for the overall Castaic Dam facility was conducted between 2022 and 2024. The Safety Assessment’s purpose was to develop and evaluate programmatic approaches to address potential dam safety and risk concerns. To accomplish this objective, the Safety Assessment:
- Identified treatment alternatives to reduce dam safety risk and improve reliability as well as resiliency of the dam facility
- Evaluated these treatment measures
- Developed programmatic approaches (PA)
- Recommended a selected PA for implementation
As DWR moves forward with the Castaic Dam Modernization Program, the safety assessment informs DWR’s prioritization of projects that will reduce risks associated with the facility. The planning-level study also identified risks that require further study to verify that action is needed through large capital improvements.
Earthquake Resiliency Assessments
- DWR conducted a stability analysis in 2018, which indicated the dam structure will continue to perform safely, even in the event of a major earthquake.
- However, other studies indicate that the outlet structures (the large towers that allow DWR to release water from the reservoir) are vulnerable to collapse in a major earthquake. While this would not cause the dam to fail, it would significantly reduce DWR’s ability to release water reliably therefore slowing the delivery of water to customers.
- In 2022, DWR completed seismic retrofits of the access bridge to the outlet structures to ensure that personnel can access the outlet structures during a major earthquake.
What to Expect
- During the modernization process, as a cautionary measure, DWR lowers the water level of Castaic Lake slightly during the winter months to provide more capacity in the reservoir to buffer winter run-off, reducing the likelihood that the spillway would need to be employed. Additionally, temporarily reduced water levels may facilitate construction efforts. These slightly lower water levels will not impact water supply and DWR is working closely with its state partners and local organizations to minimize the extent of recreation impacts.
- DWR will be operating construction equipment in all phases of the modernization program. Some localized noise and increased activity may be expected, particularly during rehabilitation construction efforts.
- DWR anticipates that the modernization efforts of the Program will take about 15 years to complete.
2019
The Stream Release Chute Investigation that included a series of core holes to assess the concrete thickness, condition, and underlying foundation of the chute was completed. The investigation confirmed the structure conforms to as-built conditions and meets structural design and stability requirements for its intended purpose.
The Toe Drain Inspection was completed and results indicate that the toe drains are functionally appropriately and as designed.
2020
In early 2020, DWR successfully completed a three-year refurbishment effort of the isolation valves to the State Water Contractor at the Castaic Outlet. The work included the refurbishment of a 42”, 72”, and 132” valves.
In November, DWR initiated field work for the Castaic Dam Spillway Geologic Investigation. This work required the use of cranes and drill rigs to advance twenty drill holes within and around the spillway to assess the complex geologic conditions underlying the structure. Instrumentation was installed to enhance the monitoring of the structure and its foundation.
2021
DWR installed additional piezometers in Castaic Dam’s left abutment. These instruments improve the monitoring of groundwater conditions in the left abutment and replace aging instruments.
DWR performed a temporary drawdown of Castaic Lake for construction of the Tower Access Bridge Seismic Retrofit Project between Summer 2021 to Spring 2022. The drawdown allowed for the seismic retrofits to the normally submerged bridge piers.
2022
The 500-foot-long tower bridge improvements were completed in February of 2022. Improvements consisted of applying carbon fiber reinforced polymer wrapping to three piers, and adding catcher blocks, shear blocks, elastomeric bearing pads, and steel members as part of the superstructure portion of the bridge.
The intake Tower Debris Mitigation Project began with a conceptual design report. This risk reduction project will help maintain State Water Contractor water deliveries in the unlikely event the high tower collapses in a major seismic event. It will also provide for dewatering of the reservoir (if needed) following a major earthquake.
2023
DWR initiated design efforts for the Castaic Dam Intake Tower Debris Mitigation Project which will install 1) a redundant dogging mechanism for the low-level intake gate and 2) a trash rack within the outlet tunnel. These features will improve the reliability of the low-level outlet system for water delivery and reservoir drawdown should earthquake damage occur. Due to the outage necessary for their installation, a flow bypass system will also be installed during construction to minimize impacts to water delivery to local agencies. DWR is coordinating closely with downstream water agencies on the duration and timing of the outage for construction, which is currently planned for 2027.
2024
DWR continued progress on the Castaic Dam Intake Tower Debris Mitigation Project and submitted an application to DSOD for the project, including 35 percent level drawings and specifications. Several coordination meetings with local water agencies were conducted to understand their minimum flow needs, discuss outage requirements, and design the flow bypass system.
The Castaic Dam Safety Assessment was completed. The Safety Assessment identified near-term as well as potential longer-term risk reduction measures for consideration. It also identified risks that require further study to justify taking action through large capital investments.
In October, DWR published a comprehensive report on the instrumentation data collected from the spillway instrumentation installed in 2021. A key finding of the report is that each extensometer and piezometer location responds differently to rainfall, reservoir influence, and the mineralogy of the bedrock. The instrument data confirms the complex geologic and geotechnical conditions encountered during construction that contribute to variable water level elevations and expansion along the spillway. Expansion is most prevalent and on-going in the upper portion of the spillway.
2025
In March, 95 percent-level drawings and specifications for the Intake Tower Debris Mitigation project were submitted to DSOD for review.
DWR is developing a plan for new dam safety instrumentation for the dam to replace aging instruments that were installed in association with the dam’s construction.
Spillway data collection will continue to understand the extent, origin (depth), and rate of expansion of the bedrock underlying the spillway. Uplift experienced since the time of construction has led to repetitive maintenance efforts. Strategies for mitigation of the uplift will continue to be investigated so that future replacement and rehabilitation of portions of the spillway will not experience similar uplift or deflections over their service life.
Castaic Lake offers a variety of recreational opportunities, such as boating and fishing. Visit the Castaic Lake web page for more information on recreation.
- Notice of Intent for Castaic Dam High Intake Tower Bridge Retrofit
- Final Initial Study/Mitigated Negative Declaration for Castaic Dam High Intake Tower Bridge Retrofit
- Notice of Determination for Castaic Dam High Intake Tower Bridge Retrofit
The California Department of Water Resources (DWR) adopted a Mitigated Negative Declaration (MND) for the proposed Castaic Dam High Intake Tower Bridge Retrofit Project. The draft Initial Study and proposed MND were prepared in accordance with the California Environmental Quality Act (CEQA) to provide agencies, the public, and interested parties an opportunity to review the environmental analysis for the proposed project.
The Initial Study was circulated for public review and comment for the period of 30 days (April 10, 2020 and ending May 10, 2020). DWR filed the Notice of Determination for the project on September 3, 2020.
DWR, the owner and operator of Castaic Dam in Los Angeles County, developed a public information toolkit to provide resources on dam safety and the Castaic Dam Modernization Program.
The toolkit’s components include:
- Table of Contents
- Introduction
- Question and Answer
- Fact Sheet
- Dam Components
- Region Map
- Sample Article
- Inundation Map
- Dam & Flood Safety Tips
- Additional Resources
- Linked Resources
Contact Us
For more information on the Castaic Dam Modernization Program, contact:
Digital Photography
News Updates
DWR completed the seismic retrofits on Castaic Dam’s tower access bridge in Los Angeles County. The completion marks a major milestone to ensure the resiliency of State Water Project facilities.
Published:
Seismic work at Castaic Dam’s tower access bridge has reached another milestone with the completion of work on three bridge piers. The work at the Los Angeles County facility is part of ongoing efforts by DWR to make the bridge stronger and reduce seismic risk at all State Water Project facilities.
Published:
DWR will begin implementing additional boating requirements at Castaic Lake in Los Angeles County due to the recent discovery of invasive quagga mussels.
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