The California Division of Safety of Dams (DSOD) released updated information last week on 1,249 dams under its jurisdiction, including downstream hazard classification, condition assessment, and reservoir restriction status for each dam.
The information reflects the most recent physical inspections and comprehensive re-evaluations by DSOD engineers and engineering geologists, as well as technical analyses performed by dam owners.
“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.”
Today’s action is part of the state’s ongoing efforts as a dam safety leader and furthers Governor Edmund G. Brown Jr.’s four-point plan to bolster dam safety by making information readily accessible. It also helps carry out legislation signed by the governor earlier this year requiring dam owners to update emergency action plans and inundation maps to incorporate new information.
DSOD works closely with dam owners to identify and correct potential issues on an ongoing basis. Dam owners are responsible for the proper operation, maintenance, and repair of their dams, and for any associated cost.
Downstream Hazard Classification
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.
The hazard classification is used in part to prioritize development of inundation maps and emergency action plans. 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.
Condition Assessments and Reservoir Restrictions
DSOD dam condition assessments are based on five condition ratings from the U.S. Army Corps of Engineers National Inventory of Dams, with some minor modifications. The ratings include satisfactory, fair, poor, unsatisfactory, and not rated. Dams rated as satisfactory have no identified deficiencies. Dams rated as fair, poor or unsatisfactory have at least one identified deficiency.
·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.
Additional Dam Safety Information
In the wake of the Lake Oroville spillways incident, DSOD initially prioritized spillway re-evaluations for 93 dams with spillways similar to Lake Oroville’s. Owners of those 93 dams 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.
Over the past 20 years, DSOD has focused its attention on conducting in-depth re-evaluations of dams located near active faults and in densely populated areas. 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.
“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.”