Repairs ordered at ‘extremely high hazard’ Nacimiento Dam

The Nacimiento Dam, which is located in San Luis Obispo County but owned and operated by Monterey County, received a classification from the state of California as being an “extremely high hazard.” California’s Division of Safety of Dams ordered repairs at the Nacimiento reservoir, as well as at the San Antonio Dam in southern Monterey County, which received the same classification.

In February, the spillway at Oroville Dam in Northern California suffered damage and began to erode. Then the emergency spillway failed, which prompted evacuations of more than 180,000 residents in the area.

Failures at the Oroville Dam prompted the Division of Safety of Dams to reevaluate large spillways at high-hazard dams. Investigators then found the same conditions that caused the Oroville Dam spillway failure exist at the San Antonio and Nacimiento dams, according to a staff report produced by the Monterey County Water Resources Agency.

The state dam agency ordered that minimum repairs be completed at the two dams by Dec. 1. The minimum repairs consist of filling joints and cracks, replacing damaged concrete, removing raised edges on downstream slabs and walls and ensuring spillway drains are functional.

Last week, the Monterey County Water Resources Agency Board of Supervisors approved spending up to $500,000 in order to complete the initial repairs on the San Antonio and Nacimiento spillways.

Earlier this year, the state also identified Lopez Dam and Whale Rock Reservoir in SLO County as “high-hazard” dams.  However, repairs have yet to be ordered at Lopez or Whale Rock.