An independent report by national dam engineering experts says “long-term systemic failures” led to the collapse last year of two spillways at the nation’s tallest dam, and subsequent mass evacuations of areas near Oroville in Butte County.
The nearly 600-page report prepared jointly by the Association of State Dam Safety Officials and United States Society of Dams cites a string of failures from flaws in the dam’s original design and construction in the 1960s, to the bedrock upon which it was built, to lapses in ongoing inspections over the decades since.
According to the report:
“The seriousness of the weak as-constructed conditions and lack of repair durability was not recognized during numerous inspections and review processes over the almost 50-year history of the project.”
The report balks at blaming any “individual, group or organization,” instead spreading responsibility over virtually everyone involved in the dam’s design, construction and operation.
In a statement, California Dept. of Water Resources Director Grant Davis (who has joined the agency since last year’s crisis), said the report is “consistent” with the findings of the agency’s own independent review, and that lessons from that were “fully incorporated in the design of the reconstructed spillways.” DWR rushed to complete a partial rebuild of the dam’s spillways before the start of the current wet season, last November.
Davis offered assurance that DWR would “carefully assess this report, share it with the entire dam safety community and incorporate the lessons learned going forward to ensure California continues to lead the nation on dam safety.”
During intense winter storms last February, water levels behind the 770-foot-high dam rose to the point where the dam’s principal spillway broke down under pressure from necessary releases into the river. When the dam’s earthen “auxilliary” or emergency spillway began to disintegrate as well, evacuation orders went out to about 800,000 people in Oroville and other communities downstream of the dam.