DWR Releases Initial Findings Regarding Lake Oroville Spillway Failure

The California Department of Water Resources today released a memo from an independent forensics team which outlines a list of factors that may have contributed to the Lake Oroville main spillway failure on Feb. 7.

Some of the possible factors for the failure include: thinning of the chute slab above herringbone drains which can promote cracking;  large variations in slab thickness; limited slab reinforcement consisting of one layer of light reinforcement in the top of the slab; and lack of continuous tension reinforcement across slab joints

According to DWR, the purpose of the memo from the forensics team is to outline the potential causes of the spillway damages to ensure that DWR considers these factors in the design of the repairs.

“This memo outlines the potential causes of the main spillway failure, which will be thoroughly investigated by the Forensics Team over the next few months,” said DWR Acting Director Bill Croyle.  “Although this is preliminary information, we are taking it into consideration as we develop plans to reconstruct the spillway.”

In a conference call briefing May 4, the team presented a preliminary list of candidate physical factors that could have potentially contributed to the initial failure mechanisms at the main spillway. The preliminary list was presented to DWR, the independent Board of Consultants (BOC), the Federal Energy Regulatory Commission (FERC), and the California Division of Safety of Dams (DSOD).

DWR has posted the Forensics Team memo online.  DWR expects to receive the team’s final report in fall of 2017 which will outline what caused the failure.

Consistent with DWR protocol, every memo from the forensics team will be posted in the same format it was received, with Critical Energy Infrastructure Information (CEII) redacted as needed CEII is considered a security risk, as it contains design details about the Oroville Dam facilities.

The forensics team is assigned to prepare an independent report on the actual contributing factors that led to the failure of the main spillway at Lake Oroville. As outlined in a Feb. 13 letter, FERC requested that DWR complete a forensic analysis aimed at determining the cause of the main spillway failure and determining if the failure mode could occur again.

Officials with the Association of State Dams Safety and the United States Society of Dams assembled the independent team of experts in April to conduct a forensic evaluation. FERC requested that the BOC and the DSOD be allowed to review and comment on the ongoing investigation, including possibly requesting additional information or analysis.

For more information visit our Oroville Spillway Incident webpage.