Potentially catastrophic problems with both the primary and emergency spillways at the Oroville Dam appear to have been caused by flaws that either had shown up in inspections or were flagged to state and federal officials going back more than a decade, an expert in infrastructure failures said.
The cratering of the main spillway — which spiraled into the current crisis in Butte County — occurred in a spot where cracks and other defects had been found repeatedly since 2009, said Robert Bea, a professor emeritus and engineering expert at UC Berkeley.
But the defects do not appear to have been adequately repaired or resolved by the state Department of Water Resources, which runs the dam, and the faulty work probably resulted in the fissure that opened up last week on the 1,730-foot-long spillway, Bea said.
“My God, we had evidence that there was trouble going back to 2008, 2009,” said Bea, who reviewed 14 dam inspections from 2008 to 2016 conducted by the Division of Safety of Dams, which is part of the Department of Water Resources.
“Yes, they had detected the defects (in the main spillway) and yes, they had put into gear remedial measures,” Bea said. “Were those repairs sufficient? No. The result was a breach.”
Critics said the state should have avoided this predicament, but chose years ago not to improve the emergency spillway by lining it with concrete.
In 2005, three environmental groups — Friends of the River, the Sierra Club and the South Yuba River Citizens League — warned state and federal water regulators about the emergency spillway in a 31-page motion filed with the Federal Energy Regulatory Commission. The dam was going through a periodic relicensing review by the commission.
The groups were concerned that use of the unpaved auxiliary spillway would cause extreme erosion, endanger fish and damage downstream structures, including a fish hatchery where millions of fish had to be rescued and moved last week.
But the more than two dozen state water contractors that receive supplies from Lake Oroville, including the mammoth Metropolitan Water District in Southern California, refused to pay the estimated $100 million cost of “armoring” the spillway.
In the end, the Federal Energy Regulatory Commission dismissed the concerns about the emergency spillway, declaring in a 2006 memorandum that “during a rare event with the emergency spillway flowing at its design capacity, spillway operations would not affect reservoir control or endanger the dam.”
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