Division of Safety of Dams releases updated information on California’s dams

By on September 7, 2017

California’s Division of Safety of Dams (DSOD) has released updated information on the downstream hazard classification, condition assessment, reservoir restriction status and other information for the 1,249 dams under its jurisdiction. The data will further guide efforts to strengthen the critical infrastructure of the state’s dams.

DSOD works closely with dam owners to identify and correct potential issues on an ongoing basis. However, dam owners are responsible for the proper operation, maintenance, and repair of their dams, and for any associated cost. DSOD’s update information reflects the most recent physical inspections and comprehensive reevaluations by DSOD engineers and engineering geologists, as well as technical analyses performed by dam owners.

The new information furthers Governor Edmund G. Brown Jr.’s four-point plan to bolster dam safety by making information readily accessible. It advances legislation signed by the governor earlier this year requiring dam owners to update emergency action plans and inundation maps to incorporate new information.

“In light of lessons learned from the Lake Oroville spillways incident, we know there is work to do to expand and strengthen our dam safety program,” DSOD Chief Sharon Tapia said. “Aging infrastructure is a serious concern, with half the dams in our jurisdiction at least 50 years old. This information will help prioritize where investments in dam safety need to be made.”

DSOD dam condition assessments are based on five condition ratings of satisfactory, fair, poor, unsatisfactory, and not rated from the U.S. Army Corps of Engineers National Inventory of Dams, with some minor modifications. Dams rated as fair, poor or unsatisfactory have at least one identified deficiency. Dams rated as satisfactory have no identified deficiencies.

  • Currently 1,151 dams (92 percent) within DSOD’s jurisdiction are rated satisfactory, meaning they have no identified deficiencies. Ninety-seven dams (less than 8 percent) within DSOD’s jurisdiction have a deficiency with a current condition assessment of fair, poor, or unsatisfactory. Forty-four of those dams have a seismic deficiency.
  • Of the 97 dams with deficiencies, DSOD records show repairs are underway by the owners on 63 dams. Records show repairs are delayed or progress unsatisfactory on the remaining 34 dams.
  • Dam condition assessments may change from year to year as repair work is completed or new deficiencies are identified.
  • DSOD may require that reservoir storage be reduced (restricted) to a specific level if unsafe conditions exist.

The downstream hazard classification identified for each dam is based solely on the size of the dam’s reservoir and population that would be impacted by a dam failure; it does not reflect the condition of the dam or its structures. Dams are classified as high or extremely high hazard if at least one person is at risk downstream in the event of a dam failure. By that definition, 670 dams (54 percent) of those under DSOD’s jurisdiction are classified as high or extremely high hazard. The hazard classification is used in part to prioritize development of inundation maps and emergency action plans.

“Dam safety is a collective effort,” Tapia said. “While owners are responsible for the safety of their dams, we need public and policymaker support to advance strong dam safety regulations and secure funding for this critical work.”

In the wake of the Lake Oroville spillways incident, DSOD initially prioritized spillway reevaluations for 93 dams with spillways similar to Lake Oroville’s. The 93 dam owners were notified this spring of requirements to submit a work plan to investigate the condition of their spillways. DSOD’s re-evaluations of those spillways are now underway.

Re-evaluations are more comprehensive than physical inspections and typically require many years and millions of dollars to complete. DSOD re-evaluations in the last two decades have resulted in dam owners investing over $1.5 billion in repairs to reduce the risk of dam failures due to earthquakes. Over the past 20 years, DSOD has focused its attention on conducting in-depth reevaluations of dams located near active faults and in densely populated areas.