DWR is beginning assessment work on Pyramid Dam’s spillways in Los Angeles County as part of a statewide effort to reduce seismic and hydrologic risk to State Water Project (SWP) facilities spanning 705 miles throughout California.
Pyramid Dam Modernization Program
Pyramid Dam and Lake are located about 60 miles northwest of downtown Los Angeles and provides water storage for the greater Los Angeles area. The dam was built between 1969 and 1973 as part of the California Department of Water Resources (DWR) State Water Project (SWP).
DWR is modernizing its SWP portfolio across the state. This includes identifying and proactively addressing any issues that could impact the delivery of water or the safety of surrounding communities. Over the next several years, DWR will conduct assessments of Pyramid Dam and undertake construction activities to ensure the dam continues to function safely.
Status of Pyramid Dam
In its most recent inspection, the California Division of Safety of Dams (DSOD) rated Pyramid Dam as satisfactory – meaning there are no existing or potential dam safety deficiencies that will impact the functioning of the dam. However, there are improvements that could be made to mitigate impacts due to an extreme weather event or earthquake. Based on the most recent DSOD findings as well as other inspection and assessment activities conducted by DWR, the initial focus of the Pyramid Dam modernization will be to assess the impacts of an extreme weather event and to conduct earthquake analyses to identify improvements for the gated spillway and the emergency spillway.
Spillways Condition and Extreme Weather Assessments
- The gated spillway at Pyramid Dam is used approximately once per year to release natural inflows and whenever inflows exceed stream release capacity.
- The emergency spillway at Pyramid dam has never been used.
- Climate models show that increased temperatures in California will result in more precipitation falling as rain instead of snow which will change river flows in the state and could impact how DWR operates the SWP facilities to manage changing precipitation patterns.
- DWR wants to ensure that the gated spillway will continue to work and that the emergency spillway will work appropriately if some future events require its use.
Earthquake Resiliency Assessments
- In 2019, DWR completed an analysis of the expected performance of the intake towers (the structures that are used release water from the reservoir) in the event of an earthquake. Damage to the towers during an earthquake would not cause the dam to fail, however it would significantly reduce DWR’s ability to release water, slowing/reducing the delivery of water to customers. If this occurred during peak water inflow to the reservoir (typically late winter and early spring), the reduced ability to release water could raise reservoir levels too much, and DWR would potentially have to use the spillway to release water and lower water to a safe level.
- DWR is also conducting seismic evaluations of the gated spillway to determine if any retrofits are necessary to ensure it will work appropriately in the event of an earthquake.
- DWR expects the assessments to be completed in 2022.
What to Expect Next
During the modernization process, DWR will be operating construction equipment which will result in some localized noise and increased activity may be expected. There are no impacts to recreation at Pyramid Lake. DWR anticipates that the modernization of the dam will take about 10 years to complete.