Following the completion of interim repairs carried out by the SFPUC to address damage from a major storm event, Moccasin Reservoir has been returned to service, supporting water reliability for the agency’s 2.7 million customers.
On March 22, 2018, heavy rainfall resulted in a surge of water and debris down several creeks Creek into Moccasin Reservoir, threatening to overtop Moccasin Dam. At no time was there a threat to the Bay Area’s water supply, and SFPUC crews were able to lower the water level in the reservoir before it overtopped the dam.
Following the incident, the SFPUC assessed damage at the site and determined that debris from the storm had damaged and blocked a crucial outlet and culverts at the facility, and the surge caused severe erosion at the toe and abutments of the Moccasin Creek Diversion Dam and along portions of the Moccasin Dam Auxiliary Spillway. The Moccasin Dam itself also suffered minor erosion, and damage to various infrastructure components—including potable water distribution lines, metal gates, fences and culverts.
SFPUC crews have completed a series of interim repairs which were divided into two phases. Phase I focused on repair of the erosion at the toe of Moccasin Dam and improving access to an outlet tower and gate valve that releases water from the reservoir.
Phase II of the interim repairs extended the core of Moccasin Dam to the full height of the dam, addressed damage to the Moccasin Creek Diversion Dam and Moccasin Auxiliary Spillway, and repaired several culverts.
The work has been sufficient for the California Division of Dam Safety to allow the SFPUC to bring Moccasin Reservoir back into service, with full capacity restored on June 6.
Moccasin Dam is a rockfill dam with an interior concrete core wall that was completed in 1930. Although it is one the SFPUC’s smallest facilities, the Moccasin Dam and Reservoir are critical to the SFPUC’s Regional Water and Power System.