B.F. Sisk Dam


B.F. Sisk Dam is a 382-foot-high zoned compacted earthfill embankment located on the west side of California's Central Valley about 12 miles west of Los Banos, California. The dam is over 3.5-miles long and impounds San Luis Reservoir, which has a total capacity of more than 2 million acre-feet.

The dam was built between 1963 and 1967 to provide supplemental irrigation water storage for the federal Central Valley Project (CVP) and municipal and industrial water for the California State Water Project (SWP). Water is lifted into the reservoir for storage by the Gianelli Pumping – Generating Plant from the California Aqueduct and from the Delta-Mendota Canal via O’Neill Forebay.

B.F. Sisk Dam (also known as San Luis Dam) is owned by the Bureau of Reclamation (Reclamation) and operated by the California Department of Water Resources (DWR). Reservoir storage space is allotted 55% state and 45% federal.

B.F. Sisk Dam Safety of Dams Modification Project

Reclamation and DWR prepared a joint final Environmental Impact Statement/Environmental Impact Report (EIS/EIR) for B.F. Sisk Safety of Dams Modification Project to reduce seismic risks at B.F. Sisk Dam in Merced County. This dam safety modification is Reclamation’s largest project under the 1978 Safety of Dams Act.  

The Crest Raise Alternative was selected as the preferred alternative. Increasing dam height will reduce downstream public safety concerns by reducing the likelihood of overtopping if slumping were to occur during a seismic event. Stability berms and other dam safety features will be added to the existing dam. By avoiding embankment failure, the proposed action will also maintain critical water supply deliveries to south of Delta CVP and SWP water service contractors.

The final EIS/EIR considered and addressed all comments received during the public review period on the draft EIS/EIR. The review period of the final EIS/EIR (available HERE) ended Sept. 23, 2019. Reclamation signed a Record of Decision (ROD) in December 2019.

The Executive Summary of the B.F. Sisk Safety of Dams Modification Report (is available HERE).

Construction Photos

  • 2020
    • May (PDF - 1 MB)

Safety of Dams Investigations Background

A series of studies and analyses culminating in the seismic risk analysis that was completed in 2006 determined that there is justification to take action to reduce risk to the downstream public from a potential severe earthquake. Consequently, Reclamation, with collaboration from DWR, initiated a corrective action study to investigate and determine a course of action to mitigate risk. This decision was a result of the following developments:

  • Increases in the estimates of both the severity of ground shaking due to nearby earthquake faults, primarily the Ortigalita fault, which crosses San Luis Reservoir and the probability of a large event on this fault
  • New understanding of the properties of the dam’s foundation materials and their ability to resist deformation when subjected to severe shaking
  • Advances in computer-based analysis methods, which allow better assessment of the behavior of the dam under seismic loading

Current Investigations and Analyses

Geology: Reclamation and DWR are performing and have completed several geologic investigations to better understand:

  • The foundation materials beneath the dam
  • As-built placement of embankment zoning
  • Borrow area locations and materials

Engineering: Feasibility level designs have been completed and development of final designs for a structural modification to address seismic risks are underway. The preferred structural alternative includes raising the dam to increase available freeboard and several downstream berms and shear keys to stabilize the embankment if exposed to earthquake shaking. This alternative also includes new zoning filter along the downstream side of the crest to protect against cracking. Feasibility level designs for a reservoir restriction and full breach of the reservoir have been completed.

Economics: An economic analysis to compare life cycle cost of each alternative is underway. The analysis is being performed using the Common Assumptions Workgroup that includes, Reclamation, DWR, and water user representatives.

Environmental: Reclamation issued a solicitation for environmental and cultural resources compliance services. DWR and Reclamation are participating in this task, which will follow state and federal guidance. Public review of the draft EIS/EIR is targeted for April 2019.

Corrective Action Study: This phase of this Safety of Dams project that developed alternatives, produced feasibility level designs, and selected a preferred alternative was completed in April 2018.

Final Design Phase: The current phase of this Safety of Dams project is referred to as the Final Design Phase. Tasks in this phase include performing additional analyses and design; preparing drawings and specifications for the structural modification; completing environmental documentation and permit application; and preparing and delivering a modification report to the federal Office of Management and Budget and to Congress. Congressional acceptance of the modification report allows funding for construction.

  • Project Status Updates for Water Users: Reclamation and DWR have been providing periodic project status updates (joint briefings) to CVP and SWP customers. The first of these joint briefings was held on April 15, 2009, at DWR’s downtown office. The last briefing was provided by Reclamation (Mynul Chowdhury) on August 23, 2018, via conference call from Reclamation’s Regional office. He sent out PowerPoint Presentation prior to the briefing. He provided updates on current status of the project including deformation analyses, CAS Alternatives and CRB recommendations. He also briefed on overall project schedule, budget and cost including final design and construction phase of the project. Both SWP and CVP water contractors agreed to have next briefing in August 2019.

Reclamation and DWR intend to notify both SWP and CVP water contractors of upcoming briefings via email. Email notifications for next briefing was targeted to go out by Jul 30, 2019.

For additional information, please contact Safety of Dams or call 916-978-5328 (TTY 800-877-8339)

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Last Updated: 3/22/22