“Complacency, bureaucracy and an inadequate safety culture led to the failure last year of the Oroville Dam spillway.” That’s the conclusion of an independent investigation team released this past Friday.

The final report by the Oroville Independent Forensic Team cited human error by several organizations, including the dam’s owner, the California Department of Water Resources (DWR).

The report described the DWR as an “insular organization, which inhibited accessing industry knowledge and developing needed technical expertise.” It also blamed the DWR for being “significantly overconfident and complacent about the integrity of its State Water Project civil infrastructure, including dams.”

Periodic inspections of the dam did not identify the original design flaws and the subsequent deterioration of the spillway’s integrity, the report noted.

The report also criticized the DWR for hiring a postgraduate engineer with no experience in spillways as one of the key Oroville spillway designers. The investigation team said, “It finds it striking that such an inexperienced engineer was given the responsibility of designing what is still the tallest dam in the U.S.”

The independent forensic team, organized by the Association of State Dam Safety Officials, put some of the oversight responsibility on the Federal Energy Regulatory Commission. But the report found no single person or organization to be fully at fault.

Cracks developed in the spillway soon after it was completed in the 1960s. The spillway began disintegrating on February 7, 2017, when a deluge from the Feather River watershed filled the dam. Over 55,000 cubic feet of water per second crashed down the ramp and the concrete structure began to fall apart.

That torrent forced operators to open the spillway gates. However, once the spillway was damaged, dam operators closed the gates. The gate closure allowed the reservoir to rise to a concrete lip, known as a weir, on the emergency spillway. It was the first time in the dam’s history that the emergency spillway had been used and water quickly eroded the bare hillside under the weir.

If the weir had failed, a 30-foot wall of water would have roared down the Feather River and into nearby communities. As a precaution, authorities issued an evacuation order for 100,000 residents of Oroville and nearby communities.

The dam held and residents were allowed to return to their homes.

The DWR is rebuilding the spillway at a cost of $500 million. Major parts of the repair were completed by Nov. 1, and additional sections of the spillway will be rebuilt in the summer of 2018.