The Independent Forensic Team (IFT) investigating the Lake Oroville spillways incident has released an interim memo highlighting their findings so far, with the team highlighting critical factors that it believes likely played the most significant roles in the failure of the service spillway chute.

The IFT says it has carefully reviewed extensive documentation related to the geology and subsurface conditions of the spillway foundations; design and construction of the spillways; inspection, evaluation, maintenance, and repair of the spillways; the California Department of Water Resources (DWR) dam safety program management; and the regulatory framework for the project. In addition, the IFT has studied photos and videos of the spillways, and post-incident forensic field investigation reports related to the failure and post-failure conditions.

It said it is nearing completion on its deliberations regarding the physical factors involved with the spillway incident and has substantially progressed its investigation of human and organizational factors. It is now focusing largely on completion of the investigation of human and organizational factors and compilation of its findings in a final report, expected in the fall.

The final report is expected to details all lessons learned following the incident, but in the memo the FIT shares three higher level lessons identified so far:

  • 1. Physical inspections, while necessary, are not sufficient to identify risks and manage safety. At Oroville Dam, more frequent physical inspections would not likely have uncovered the issues which led to the spillway incident.
  • 2. Comprehensive periodic reviews of original design and construction, taking into account comparison with the current state of the practice, are needed for all components of dam projects.
  • 3. Compliance with regulatory requirements is not sufficient to manage dam owners’ and public risk.

Commenting on the interim memo, the Department of Water Resources (DWR) said that protecting public safety is the state’s top priority, and it is committed to applying lessons learned from Oroville.

In a statement it said: “DWR agrees with the IFT that dam owners need to reassess current procedures as visual inspections would not have caught the February failure. The additional spillway evaluations already underway are the start of that process.

“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.

“The IFT’s findings and recommendations are relevant not just for Oroville or DWR but for all dam owners. The IFT’s research will push the entire dam safety community forward to make lasting changes and improvements internationally.

The IFT shared this information ahead of their final report to inform ongoing spillway evaluations at other projects and educate the dam safety community. DWR is grateful for the team’s work and thanks the Association of State Dam Safety Officials and the United States Society of Dams for choosing this independent team of world-renowned experts with specialties in dams and spillways.”

View the full interim memo here.