Castaic Dam Modernization Program

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.

 

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

Spillway Condition and Extreme Weather Assessments

• 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 continue to function appropriately. 
• 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. Recent studies indicate that the spillway is still expected to function as intended if activated, even during 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 weather pattern uncertainties and potentially larger inflows, DWR is ensuring that the spillway will function appropriately if it is needed to release water in the future. 

Safety Assessment

A Safety Assessment for the overall Castaic Dam facility is being performed, starting in early 2022. The Safety Assessment’s purpose is to develop and evaluate programmatic approaches to address potential dam safety and risk concerns. To accomplish this objective, the Safety Assessment will:

• Identify treatment alternatives to reduce dam safety risk and improve reliability as well as resiliency of the dam facility
• Evaluate these treatment measures
• Develop programmatic approaches (PA)
• Recommend a selected PA for implementation

As DWR moves forward with the Castaic Dam Modernization Program, the safety assessment will inform DWR’s prioritization of projects that will reduce risks associated with the facility, as well as those projects within the State Water Project.

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 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 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.