Litany of errors at Oroville Dam
Decades of complacency, inadequate repairs caused near-disaster, report finds
The spillway failures at Oroville Dam that prompted tens of thousands to flee for their lives last winter were the result of years of mistakes, lax inspections and lazy repairs by the state’s water agency, a team of independent dam experts reported Friday.
Their conclusions: State water managers should not have built the dam’s primary spillway on faulty bedrock. They should have done more when the spillway’s concrete began to crack and water seeped through. And they should have been on high alert when the ground below began to give way.
Instead, during nearly 50 years of preventable decay, the California Department of Water Resources did only a few patch jobs on the half-milelong water chute, leading up to its disintegration in February and prompting wider concern about how the state maintains its other nearly three dozen water storage sites.
The six-person team charged by federal regulators with investigating the nation’s tallest dam has pointed out several of the structural deficiencies in previous reports, but its latest and final assessment links them to a steady run of human missteps.
The 584-page document describes a culture of complacency, overconfidence and insularity at the Department of Water Resources that allowed errors to compound earlier errors, dating back all the way
to the dam’s construction in the 1960s.
Although the authors say state managers had numerous opportunities to prevent spillway problems, they don’t blame any individual. Nor do they identify a single root cause behind the dam’s flaws.
“Although we’re recommending that DWR look at its organization and improve, many of the lessons apply to other dam owners as well,” said John France, a geotechnical engineer and head of the review team. “As a group, our industry needs to improve what we’re doing.”
State water officials said Friday they are still reading the report but that they take the findings seriously.
“As we have done in the past, we will 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,” said Grant Davis, director of the Department of Water Resources.
The report notes that the Federal Energy Regulatory Commission, the agency tasked with inspecting all dams that generate electricity, also failed to spot long-standing issues at Oroville Dam, as did several consultants who worked with the state.
The report calls the repeated oversights a “wake-up call” for everyone responsible for dam safety.
“People should not lose sleep over this, but they should be concerned,” France said.
The problems at 770-foottall Oroville Dam, located about 75 miles north of Sacramento, became obvious to everyone on Feb. 7. A section of the giant spillway fractured as large volumes of water poured out of the reservoir, prompting dam operators to turn to an emergency spillway, essentially a barren hillside, to make releases. The backup chute, however, also began to fall apart.
Fears that water would pour uncontrollably out of the lake prompted officials to order evacuations for 180,000 people living downstream.
The new report takes issue with how state water officials handled the crisis as well. The slopes of the emergency spillway were geologically unsound and not tested, according to the document, and dam operators should not have allowed water releases there.
As it turns out, dam operators were able to use the broken main spillway to make safe releases and prevent the reservoir from overflowing. The report’s authors say the primary chute should never have been taken out of service.
“The decisions were made with the best of intentions,” the report said, “but against the advice of civil engineering and geological personnel.”
The panel’s assessment dates the issues at the dam to even before the first concrete was poured. The ground beneath both the primary and backup spillways was not as strong as it should have been, the authors say, and few at the Department of Water Resources took note initially or in the ensuing years.
“Although the poor foundation conditions at both spillways were well documented in geology reports, these conditions were not properly addressed in the original design and construction, and all subsequent reviews mischaracterized the foundation as good quality rock,” the report said.
The person who designed the spillway, the report said, had only “limited experience” with such work.
Shortly after the dam was built, cracks emerged on the main spillway, according to the assessment. Rather than recognize a problem, dam managers assumed the fractures were normal.
The report identifies five fixes that were done on the main chute as the cracks widened, one as late as 2013. But none got to the heart of the problem. According to the panel, water seeped into the ground and slowly ate away at the soil and the spillway’s anchors. In addition, the drains proved insufficient.
The dam’s damaged spillways have since been mostly rebuilt in what amounted to one of the fastest construction projects in modern state history. The costs so far have totaled $500 million.
In the wake of February’s scare, state water officials have begun a review of Oroville Dam as well as evaluations of spillways at other reservoirs.