Official forensics team releases first analysis of what went wrong at Oroville Dam

In a report released Wednesday, engineers assigned to investigate the February failure of Oroville Dam’s main spillway cited a variety of flaws in the 3,000-foot-long structure, including variations in the thickness of the concrete slabs, poor drainage beneath the spillway, improperly filled cracks and signs of inadequate maintenance.

The forensics team, consisting of six outside consultants, also said the spillway may have split because of an increase in water releases just prior to the Feb. 7 incident.

However, the team warned that its analysis, which consists of 24 possible causes, is preliminary. “Additional factors may be identified as the investigation proceeds,” the group wrote in a three-page memo to the state Department of Water Resources. The team is expected to make its final report this fall.

The preliminary report represents the first analysis by the team officially designated by DWR to determine what caused the dam’s main flood-control spillway to break apart. DWR was ordered to hire the forensics team by the Federal Energy Regulatory Commission, which licenses the dam and approved DWR’s selection of the team members. The team turned in its preliminary analysis to DWR last week, but the state didn’t release its contents until Wednesday.

Among the possible causes, the team took aim at DWR’s maintenance of the structure over the years, pointing to “lack of durability and effectiveness of slab repairs.”

One engineering expert said preliminary findings looked right – with one key exception.

Bob Bea, of the Center for Catastrophic Risk Analysis at UC Berkeley, said the memo lacked analysis of the institutional deficiencies that allowed the problems to persist. In past infrastructure failures, those issues accounted for almost 80 percent of why problems developed and went uncorrected, said Bea, a retired engineer whose credentials include conducting an independent investigation into why the levees…

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