Slowly – but surely – we are learning that the near-catastrophic failure of Oroville Dam’s main spillway wasn’t truly caused by weather, even though the state claims that in seeking federal aid for repairs.

Rather, it resulted from poor engineering and construction when the nation’s highest dam was rising more than a half-century ago as the centerpiece of the State Water Project, and poor maintenance since its completion.

The latest evidence is a huge report by a team of engineering experts, headed by Robert Bea and Tony Johnson of the University of California’s Center for Catastrophic Risk Management.

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It concluded that the dam’s fundamental flaws were compounded by decades of neglect by the state Department of Water Resources (DWR) and the Division of Safety of Dams (DSOD).

“The gated spillway was managed to failure by DWR and DSOD,” the damning – no pun intended – report declared.

One of the most abysmal failures cited was “the recently exposed existence of DSOD inspection reports dating back to 1989. For reasons yet to be fully determined, identified deficiencies were either ignored, treated as low priority, not acted upon or a combination thereof.”

The 124-page report added that “complacency, lack of industry standard level maintenance, and possibly pressure from internal DWR management and external State Water Contractors’ representatives to hold down maintenance costs were key contributors.”

Finally, and most ominously, the study team suggested that Oroville’s problems are not confined to the spillway, whose collapse last February led to the near-failure of an auxiliary spillway, a threat of failure in the dam itself, and massive evacuations of those living along the Feather River north of Sacramento.

The Bea-Johnson report says the dam may be “facing a breach danger from a serious and dangerous form of a slow-motion failure mode” through leaks in the dam caused by shifting of fill material. The sensors that are supposed to detect such shifts stopped working many years ago.

DWR has insisted all along that despite the spillway failure, the earthen-fill dam itself is “sound and safe.”

Shoddy engineering and design and neglectful maintenance in such a huge, and hugely important, structure is serious business. If what Bea, Johnson and the other experts say is accurate, it may explain why state officials from Gov. Jerry Brown downward have been so closed-mouthed about what went wrong.

After all, if it wasn’t the weather, but human error, that created the problem, then the state’s plea for federal aid is bogus.

But there’s an even more pertinent question raised by the Bea-Johnson study – whether the state is even capable of competently building and maintaining huge public works projects.

One recalls the more recent example of the San Francisco-Oakland Bay Bridge, one third of which was replaced after the 1989 Loma Prieta earthquake revealed the section’s flaws.

It not only took a quarter-century to design and build the futuristic replacement, but costs wound up four times their original estimate and after it was completed, it was revealed that there were major construction flaws that the Department of Transportation didn’t disclose but investigative journalism by The Sacramento Bee exposed. When asked about it, Brown infamously replied, “Shit happens.”

Meanwhile, Brown wants the state to build two more mega-projects.

One would bore water tunnels to carry Oroville Dam’s water beneath the Sacramento-San Joaquin Delta and complete the State Water Project that was the proudest achievement of his father, Pat Brown. The other is a north-south bullet train.

If Oroville Dam and the Bay Bridge set the standard for how the state does such things, maybe the tunnels and the train are disasters waiting to happen.