State rates 22 of 23 East Bay Municipal Utility District’s dams with its highest rating of “satisfactory”

By on September 7, 2017

The recently released State of California Division of Safety of Dams’ (DSOD) new classification and assessment of the state’s dams has rated all but one of East Bay Municipal Utility District’s (EBMUD) dams with its highest rating of “satisfactory.” The one outlier – the Tower at Lafayette Dam, built in 1927 – receive a rating of “fair.”

Lafayette Dam is still capable of being operated safely in current, or traditional, conditions. But a rare event such as an earthquake or a rare hydrological condition could compromise the Lafayette Reservoir. Due to the seismic vulnerability of its outlet tower and its location upstream of a populated area has resulted in the “fair” rating. A tower failure would affect EBMUD’s ability to release reservoir water but the impact to the Lafayette community would be limited.

EBMUD proactively inspects, upgrades and improves these dams and water supply structures as needed and in consultation with DSOD. Water district engineers monitor each of the 23 dams using instruments, monthly visual inspections and periodic dam safety reviews to protect public safety, prevent property damage and prevent personal injury from the failure of dams. The safety of each dam is also reevaluated with advances in geotechnical, structural and earthquake engineering.

In additional the district’s proactive inspections and monitoring EBMUD works in consultation with DSOD. Regulatory agencies also perform independent annual dam inspections.

In the unlikely event of a rare event that damages the Tower at Lafayette Dam the limited impacts to the Lafayette community are three-fold:

  • If 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 thereby reducing the amount of water that may need to be pumped out manually to reduce any erosion.
  • The Lafayette Reservoir is a small watershed that does not yield significant runoff from local precipitation. Therefore, there is low likelihood that runoff could exceed the reservoir’s capacity should a tower failure occur; EBMUD maintains 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.
  • If a tower failure caused 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.

The Tower at Lafayette Dam was slated for retrofit in 2022. In light of the recent new classification and assessment by the stte, EBMUD is now working with DSOD to complete the retrofit sooner. Funding for the retrofit has been identified in EBMUD’s approved Capital Improvement Budget and can begin once all regulatory, design and environmental reviews are secured.

As part of the environmental review process, EBMUD will include outreach to the Lafayette community. The district is cognizant of the importance of communicating with the community and understands how much the community values the reservoir and its features. Currently, EBMUD is upgrading both Lake Chabot Dam in San Leandro and Upper San Leandro Reservoir Dam in Castro Valley.