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SAN FRANCISCO — Bad design and construction of the tallest U.S. dam a half-century ago and inadequate state and federal oversight since then led to a disastrous spillway collapse in February, an independent national team of dam safety experts said Tuesday as they urged tougher safety reviews nationwide.

The experts investigating February's spillway failures at California's Oroville Dam say the state probably could have detected the problems that led to the collapse if dam managers had assessed the original construction flaws in the 1960s-era structure in light of modern engineering standards.

Clues to the crisis "were all in the files" of California officials, showing the original flaws in the spillways' foundation, concrete and drainage, said John France, speaking for the expert panel formed by national dam-safety associations.

At Oroville Dam, "there has never been an evaluation completely that went back thoroughly in the files," as far as the outside experts could determine, France said.

Erin Mellon, a spokeswoman for California's Department of Water Resources, the owner of the 770-foot-high (235-meter-high) dam, said state officials are committed to applying lessons learned from Oroville.

"The reconstruction efforts at Oroville will bring the spillway design and construction up to today's standards to ensure we address the physical causes that led to the February failure," Mellon said.

Fearing an uncontrolled release of massive amounts of water, authorities ordered nearly 200,000 people to evacuate Feb. 12 after both spillways at Oroville Dam collapsed. The release did not happen, but residents and farms downstream have filed more than $1 billion in claims for damages they blame on the state's deliberate water releases from the dam to deal with the crisis.

Assessing whether similar problems lie unseen in other old dams around the country depends partly on whether authorities budget the money for those historical reviews, France said. The average dam in the United States was built more than a half-century ago using now-outdated design standards.

Experts from the national Association of State Dam Safety Officials and the U.S. Society on Dams are conducting their own joint review of the causes of the Oroville crisis for safety lessons, while state and federal officials also have initiated investigations.

Tuesday's report says water entering through cracks or repair seams in the main spillway may have triggered crumbling of the spillway. It cites a series of problems with the original construction of the spillway in the 1960s, including thin concrete, poorly placed drains and inadequate foundations.

Inspections alone would not have been enough to deal with the original flaws, the experts said.

However, a thorough review of flaws built into the dam originally "would likely have connected the dots ... by identifying the physical factors that led to failure," the report said.

Existing federal regulations may already require that kind of historical review of a dam's original construction, France said. He later added, however, that industry experts are looking into whether there was "some wriggle room in interpretation" of those rules.

The federal regulations require outside consultants to conduct a thorough safety review of the dams every five years, including "due consideration of all relevant reports" on the dam by government agencies or consultants, as well as a "review and assessment of all relevant data."

Oroville's managers believe no existing regulation requires the kind of historical review the experts recommended Tuesday, Mellon said.

Federal agencies have made such evaluations of the original design and construction of federal dams a routine part of safety inspections for years, although most states rely instead on physical inspections of the structures, France said.

How To Help

Operation Blanket’s next blanket drive is scheduled for Dec. 22 from 10 a.m. to 2 p.m. at Coddingtown Mall in Santa Rosa. The organization accepts new or gently used blankets for donation.

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Oroville Dam for a time in the 1960s was the tallest dam in the world, and a point of pride for the United States as it vied with the Soviet Union for prestige globally during the Cold War. Thirty-four people died in the construction of the dam, and dam experts allege corners were cut in its building.

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