An engineering expert who visited the troubled Lake Oroville reservoir said this week that it would be nearly impossible for the state to complete temporary repairs to its fractured and eroded main spillway by a target date of Nov. 1.
In a report submitted to the Federal Energy Regulatory Commission this week, a panel of five independent consulting engineers warned that “a significant risk would be incurred” if the main spillway was not operational after October, which is the traditional start of California’s rainy season.
However, an engineering and risk management expert who was not part of the consulting panel told The Times this week that he doubted the state could meet such a close deadline.
“I think that is a challenging timeline,” said Robert Bea of UC Berkeley’s Center for Catastrophic Risk Management.
Bea, a retired civil engineering professor who led an investigation into failure of the New Orleans levee system after Hurricane Katrina, visited the reservoir recently to review inspection documents, as well as the report by the Independent Board of Consultants.
The consultants proposed that temporary repairs to the spillway be completed by Nov. 1, and that permanent repairs be completed after the rainy season.
In order to accomplish this, report authors said the Department of Water Resources should award grading contracts by March 31, complete design plans by mid-May and approve a construction contract by June 1. That would give the company five months to complete the work, the report suggested.
Bea said that schedule leaves little space for unanticipated problems.
“Previous experience with these kinds of ‘rushed’ field construction projects clearly indicates — expect the unexpected,” Bea said. “There will be delays that result in extension of optimistic schedules.”
According to department spokeswoman Lauren Bisnett, the agency is still formulating a plan of action.
“We are in the process of analyzing alternative approaches, both temporary and permanent, and we expect to detail that process and preferred alternatives within the next weeks,” Bisnett wrote in an email Friday.
She said the agency was committed to completing the job on time.
“DWR has stated from the beginning that our objective is to have a fully functional spillway before the start of the next storm season — response and recovery efforts are being expedited to make that happen.” Bisnett wrote.
The spillway, although not part of Oroville Dam itself, is the primary means of releasing water from Lake Oroville in a controlled fashion. Without it, water levels would steadily rise until the reservoir overflowed and flooded the Feather River and surrounding communities.
A steeply sloped stretch of concrete some 3,000 feet long, the main spillway is as wide as a four-lane highway. Water released from the reservoir can speed along the channel at more than 50 miles per hour, and the force it exerts on the concrete is tremendous.
After half a century of service, those forces finally hammered through the spillway’s concrete deck and caused a major crisis in February, when more than 100,000 area residents were evacuated.
Since then, the Department of Water Resources has scrambled to shore up and stabilize erosion at the main spillway and an earthen emergency spillway.
The agency has also had to perform a delicate balancing act as it alternates between conducting repairs to the main spillway and using it to release runoff from a record season of rain and snow.
The result has been a yo-yo effect with the reservoir’s water level.
Bill Croyle, acting director for the agency, estimated that crews may have to release water down the main spillway two more times before June.
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