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.
Castaic Dam Modernization Program
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.
Castaic Dam Modernization Components
Castaic Dam and Lake Statistics
Height: 425 feet Storage Volume: 323,700 acre-feet or 105.5 billion gallons
Length: 4,900 feet Surface Area: 2,240 acres
Status of Castaic Dam
In its most recent inspection, the California Division of Safety of Dams (DSOD) rated Castaic Dam as fair – meaning there are no existing dam safety deficiencies that will impact the dam’s functions under normal conditions. However, improvements can be made to prevent serious impacts after either an extreme weather or earthquake event.
Based on DSOD findings and DWR’s inspections, the initial focus of the Castaic Dam modernization effort will be to explore the conditions of the spillway, left abutment (where the dam meets the valley wall), water supply outlet structures, and the tower access bridge to the water outlets.
Spillway Condition and Extreme Weather Assessments
- Over the years, DWR has carefully and consistently managed the reservoir’s water levels so that the spillway would not be activated, even during extreme weather events. However, changes in weather patterns introduce new uncertainties for future extreme weather events. 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. To account for these uncertainties and potentially larger inflows, DWR is ensuring that the spillway will function appropriately if it is needed to release water in the future.
- Dam safety engineers have identified that some of the concrete wall and floor panels in the spillway have shifted, which could lead to erosion if the spillway were used to release water. DWR is investigating the causes and impacts to target rehabilitation work and ensure the spillway will work appropriately if a need ever arises.
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.
- DWR is currently conducting seismic retrofits of the access bridge to the outlet structures to ensure that personnel can access the outlet structures should an earthquake occur.
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 be necessary to conduct various repair efforts of the outlet towers and access bridge. 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 10 years to complete.
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.
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 requires 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 will also be installed to enhance the monitoring of the structure and its foundation.
In April, installation of additional piezometers in Castaic Dam’s left abutment began. These instruments will improve the monitoring of groundwater conditions in the left abutment and replace aging instruments.
In May, DWR plans to initiate a temporary drawdown of Castaic Lake to allow for the Tower Access Bridge Seismic Retrofit Project to be performed between Summer 2021 to Spring 2022. The drawdown will allow for the seismic retrofit to the tower access bridge, including the submerged bridge piers.
Castaic Lake’s temporary drawdown starts May 2021 to allow for seismic retrofitting to begin on Castaic Dam’s intake tower access bridge and bridge piers. The lake will reach a low elevation of 1,380 feet above mean sea level (this equals 135 feet lower than the maximum operating water elevation) in Fall 2021. After the Tower Access Bridge Seismic Retrofit Project is completed, the filling of Castaic Lake will begin by Winter of 2022.
To view Castaic Lake water storage during this project, see weekly reservoir storage chart for Castaic Lake.
During Castaic Lake’s drawdown, all visitors are advised to stay safe during fluctuating water levels by being aware and staying away from marked and unmarked hazards in the water.
Hazards Buoys will have a diamond shape on the buoy warning of hazards, such as rocks, shoals, or turbulent waters. Visitors should always proceed with caution as not all hazards may be visible.
The 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.
For more information on the Castaic Dam Modernization Program, contact:
DWR will begin implementing additional boating requirements at Castaic Lake in Los Angeles County due to the recent discovery of invasive quagga mussels.
DWR began construction on Castaic Dam’s tower access bridge in Los Angeles County to reduce seismic risks during a major earthquake.
Two key projects are set to begin as part of ongoing modernization work at Castaic Dam in Los Angeles County to reduce risks from a major earthquake. DWR will oversee the installation of new equipment to monitor the dam’s stability and work to strengthen the dam’s intake tower access bridge.