(TNS) - Potentially catastrophic problems with both the primary and emergency spillways at the Oroville Dam in Northern California 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 Monday.



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 at The Chronicle’s request 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.”



The cause of the fissure in the main spillway has not been identified. The Department of Water Resources, which runs the dam, has defended its management of the main spillway — saying it was inspected routinely — and its handling of the situation.



Bill Croyle, the agency’s acting director, said Monday, “This was a new, never-happened-before event.”



The disintegration of a section of the main spillway forced the state on Saturday to use the dam’s emergency spillway, which sends water over a bare hillside and had not been used since the dam’s completion in 1968.



Within 24 hours, erosion was threatening to burrow through the hillside and cause the emergency spillway to fail, prompting the evacuation of more than 180,000 people from downstream communities.



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.



The threatened failure “was entirely predicted and warned about, and DWR refused to even do a study,” said Deirdre Des Jardins, principal with California Water Research, which collaborates with environmental, fishing and local groups on water research projects. “If Metropolitan’s headquarters were down from the dam, you can bet they would have” agreed to pay.



Jeff Kightlinger, Metropolitan’s general manager, said the contractors had spent as much as $90 million to extend the dam’s federal license and believed paving the emergency spillway was a flood-control issue under the jurisdiction of the U.S. Army Corps of Engineers.



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.”



“We took no position on whether it should be paved or not,” Kightlinger said, “and then FERC looked at it and said it was not an issue because it would rarely if ever be used.”



As recently as 2014, the danger was spelled out in a flood management plan commission by the Department of Water Resources.



“The unlined emergency spillway for Oroville Dam would likely suffer heavy damage in the event it must be used in a major flood event,” the state report said.



Croyle said he could not comment on the complaints about the emergency spillway, because he was unfamiliar with them. Gov. Jerry Brown, asked at a news conference Monday about the decades-old warnings by environmental groups, said, “Glad we found out about it.”



The emergency spillway was briefly mentioned in the latest state inspection of the dam last August. The concrete weir or rim “remains stable appearing and in good condition,” inspectors noted, but they made no mention of the integrity of the hillside below.



Another engineering expert who reviewed the Oroville Dam’s inspection records said he did not find anything negligent in the state’s management.



Art Schmidt, president of New York-based Underwater Consultants International Inc., said inspection records show that state and federal agencies were regularly testing and evaluating the dam, including addressing cracks and other potential problems.



“I don’t see anything grossly negligent here, by any means,” said Schmidt, whose company has been conducting dam inspections for more than 20 years. “Unfortunately, structures fail. But it looks like they were doing everything that normally should be done. They were inspecting on a regular basis and monitoring defects. Obviously, something failed before they thought it was going to.”



Bea, who has analyzed disasters including the deadly 2010 pipeline explosion in San Bruno, said the first indication of trouble in the main spillway was in 2009, when defects in the base slabs, which form the concrete chute, were detected.



The situation got worse, and repairs were made in 2013, said Bea, who obtained photographs showing construction in the same spot as this month’s rupture. More repairs were made in that area in 2014 and then in 2015, he said, when cracks were detected in the spillway.



Bea said inspectors noticed trees growing on the right side of the spillway in their 2015 report. The inspectors recommended removing the trees, but the damage may have already occurred.



“Those trees are there because they like water, and the question is, where are they getting the water from?” Bea said. “The answer is that we’ve got seepage in that spillway.”



Inspectors noted in the two latest inspection reports, in 2015 and 2016, that they did not walk the main spillway, but instead viewed it from a distance — and found no problems.



In response to the crisis, the Federal Energy Regulatory Commission on Monday ordered the Department of Water Resources to perform a “forensic analysis aimed at determining the cause of the chute failure.”



Peter Fimrite, Cynthia Dizikes and Joaquin Palomino are San Francisco Chronicle staff writers. Email: pfimrite@sfchronicle.com, cdizikes@sfchronicle.com, jpalomino@sfchronicle.com



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