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 in early September as they urged tougher safety reviews nationwide, The Associated Press reports.
The experts investigating the Oroville Dam spillway failures 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 “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 The Association of State Dam Safety Officials (ASDSO) and the United States Society on Dams (USSD).
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, AP reported France as saying.
California’s Department of Water Resources spokesperson Erin Mellon 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.
The Sept. 5 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 in September, 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.