Calif. dam investigators say visual inspections can't predict failure, and could be a nationwide problem

Forensic investigators say there were plenty of red flags that could have alerted inspectors before the , disastrous flood from California's Oroville Dam, and they hope other dam inspectors are paying attention. In an interim report Sept. 5, investigators said "The state and federal officials who inspected Oroville Dam relied too heavily on visual inspections, ignoring blueprints, construction records and other documented clues that could have warned them about the dam’s troubled flood-control spillway long before it fractured in February. The fracture led to near-catastrophe and the evacuation of thousands of residents," Dale Kasler and Ryan Sabalow report for The Sacramento Bee.

Many U.S. dams are rated "high hazard." Click on FEMA map to enlarge it.

The investigators were hired by the state's Department of Water Resources to study the cause of the flood. They aid the spillway fracture was probably caused by cracks in the concrete and a faulty drainage system under a sometimes too-thin concrete chute. "Visual inspections alone, conducted annually by DWR and once every five years by the federal government, wouldn’t allow regulators to pull all the clues together and point to the likelihood of failure," the Bee reports.

The investigators say similar problems could be happening in other dams all over the country, and inspectors may not catch them if they continue to overrely on visual inspections. "The panel called on regulators to supplement visual checks with painstaking reviews of original design and construction specifications, as well as maintenance records, with an eye toward finding 'design shortcomings' that contrast with current state-of-the-art practices," the Bee reports. "The reviews should go beyond spillways and take in the entire dam structure."

Federal dam inspections are handled by the Federal Energy Regulatory Commission. In May, FERC said it was re-evaluating dam safety inspections because of Oroville. FERC's most recent inspection of the Oroville dam in 2014 "concluded that the a failure of the flood-control spillway at Oroville was so unlikely that there was no need to plan for such an emergency," the Bee reports.