Pyramid Dam Modernization Program

Crews install piezometers on the gated spilway for the Pyramid Dam Modernization project in Los Angeles County, California.

Crews install piezometers on the gated spilway for the Pyramid Dam Modernization project in Los Angeles County, California. DWR/2019

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.

Project Updates and Timeline:

  • After DWR completed an analysis of the expected performance of the intake tower in 2019, a second more detailed study was initiated to quantify the potential failure points on the intake tower. Preliminary findings indicate damage to the tower during high seismic events, but would not result in a dam failure. This Linear Elastic Time History Analysis is anticipated to be completed by Fall 2021.
  • In March 2020, DWR completed both the gated and emergency spillway assessments and field investigations, that began in September 2019. DWR engineers, geologists, and consultants assessed the 860-foot-long gated and 900-foot-long emergency spillways at Pyramid Dam by climbing a combined 530 miles and performing 450 helicopter flights in nearly 200 project days. The investigation included 25 drilled core holes on the gated spillway to verify the slab thickness and 41 drilled core holes on the emergency spillway to obtain characterization of the rock composition for the emergency spillway and the left and right abutments of the dam. DWR’s intends to complete data reports from these investigations by the end of 2021.
  • Studies on the structural integrity of the Gated Spillway are on-going, incorporating invaluable data and other information from the 2019-2020 investigation. 
  • DWR plans to facilitate the Pyramid Dam Safety Assessment by spring of 2022. This Safety Assessment is intended to identify measures (physical modifications or operational) if applicable to increase the resiliency and functionality of the Pyramid Dam facility.   

Pyramid Dam Toolkit

DWR, the owner and operator of Pyramid Dam in Los Angeles County, developed a public information toolkit to provide resources on dam safety and the Pyramid 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


Pyramid Dam Modernization Components

Pyramid Dam component graphic April 2021

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