Oakland, September 1, 2017
Latest dam assessment confirms EBMUD dams are reliable
21 EBMUD Dams receive highest state rating; Tower at Lafayette Dam - already slated for seismic retrofit - rated 'Fair'
Today, the State of California Division of Safety of Dams (DSOD) is releasing a new classification and assessment of dams statewide. Nearly all of EBMUD’s jurisdictional dams – 21 in total – were assessed the highest rating of “satisfactory”.
One dam – Lafayette Dam, built in 1927 – was assessed a “fair” rating. A “fair” rating means the dam can be operated safely in current conditions, but could be imperiled in rare events like earthquakes or hydrological conditions. Lafayette Reservoir was determined to be in fair condition due to the seismic vulnerability of its outlet tower and its location upstream of a populated area. The impact of a tower failure that affects EBMUD’s ability to release water from the reservoir is expected to have limited impacts to the Lafayette community because:
- The Lafayette Reservoir is a small watershed that does not yield significant runoff from local rainfall. There is low likelihood that runoff could exceed the reservoir’s capacity should a tower failure occur, as we maintain reservoir levels to provide adequate runoff capacity. In the event of damage to the outlet, EBMUD would deploy portable pumps to further drain the reservoir if needed and then repair the outlet line.
- Should a failure cause the outlet structure to remain open, water flows through the outlet pipe are limited to approximately 5 cubic feet per second to Lafayette Creek. This flow rate is comparable to typical creek flows.
- Should the embankment or drain line deform or rupture during an earthquake, the drain line could cause erosion. To address this issue, EBMUD is lowering reservoir levels, reducing the amount of water that may need to be pumped out manually to reduce any erosion.
EBMUD has planned and budgeted for a tower retrofit in 2022. However, we are working with DSOD to complete the work sooner. This work is identified in EBMUD’s approved Capital Improvement Budget and can begin once all regulatory, design and environmental reviews are secured. The environmental review process will include outreach to the Lafayette community, as EBMUD understands how the community greatly values the reservoir and its features.
EBMUD maintains 22 reservoirs and dams overseen by DSOD to store and secure the water supply for 1.4 million East Bay residents. The District proactively inspects, upgrades and improves these dams and water supply structures as needed and in consultation with DSOD. EBMUD has a comprehensive Dam Safety Program. Engineers monitor dams using instruments, monthly visual inspections and periodic dam safety reviews to protect public safety, prevent personal injury and prevent property damage from the failure of dams. The safety of each dam is reevaluated with advances in geotechnical, structural and earthquake engineering. Regulatory agencies also perform independent annual dam inspections. Currently, EBMUD is upgrading both Lake Chabot Dam in San Leandro and Upper San Leandro Reservoir Dam in Castro Valley.