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 measures 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.
  • The gated and emergency spillway assessments and field investigations that began in September 2019 were completed in March 2020. 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. Data reports from these investigations were completed in 2021 and 2022.
  • The gated spillway investigation’s findings have led to maintenance actions and improvements in the routine inspection, surveillance, and monitoring of the spillway.
  • Erodibility analyses for the unlined emergency spillway indicate that while erosion and damage to the spillway may occur, the potential for erosion to headcut back to the spillway weir and reservoir is remote, even under extreme flow conditions.
  • DWR continues to implement a winter operations plan that lowers the reservoir level between December and March to reduce the likelihood of emergency spillway 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 may 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 emergency spillway to release water and lower water to a safe level. The winter operations plan reduces the risk associated with this combination of extreme weather and a seismic event.
  • 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 2023.

Project Updates and Timeline:

  • In 2020-2021, DWR conducted a pilot Periodic Risk Analysis (PRA) for Pyramid Dam in alignment with Federal Energy Regulatory Commission Draft Engineering Guidelines for a semiquantitative “Level 2” risk analysis.  This effort aligned with DWR’s transition to risk-informed decision making for investments in the SWP.  
  • In fall of 2022, DWR initiated the Pyramid Dam Safety Assessment which is leveraging the investigations and studies performed over the past few years to examine, evaluate, and prioritize potential vulnerabilities to the facility and identify potential risk reductions measures that DWR may consider implementing as part of its overall risk management of the SWP. DWR will incorporate the potential failure modes identified in the Pyramid Dam Level 2 Risk Analysis, as well as standards-based safety criteria considering the age of the facility and changes in engineering practice.  DWR anticipates the Pyramid Dam Safety Assessment to complete in early 2024.
  • The Modernization Program is expected to take about 10 years to complete.  Any large infrastructure improvements identified by the Program and selected by DWR for implementation may take longer than 10 years to fully implement considering environmental, regulatory, right-of-way, design, and construction processes.
  • In mid-2023, DWR will be initiating the Director’s Safety Review Board and FERC Part 12D Independent Consultant Safety Inspection processes which provide for independent dam safety reviews of Pyramid Dam and its appurtenant structures.  These independent reviews occur every five years and are required by California Water Code and federal regulations respectively.  Recommendations provided through these processes may result in additional studies and risk reductions measures for DWR’s consideration.

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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