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Oroville Dam: Report places blame on decades of neglect, human error

Potential disaster in early 2017 was result of years-long systemic failure, says independent review

Then And Now: California's Drought Officially Declared To Be Over
A view of the damaged spillway in April 2017.
Photo by Justin Sullivan/Getty Images

During the torrential downpours of early 2017, Butte County’s Oroville Dam—the tallest dam in the United States, which creates a reservoir capacity of roughly 3.5 million acre feet and generates enough electricity to power 737,000 homes per year—nearly suffered a complete disaster that would have destroyed the homes of tens of thousands of Californians.

There was never any danger of the dam itself failing. But the reservoir was dangerously full, and the emergency spillways designed to channel excess water safely away were so badly damaged that they nearly collapsed and unleashed a “three-story wall of water” on population centers below.

Good luck and hard work kept that from happening. However, in the aftermath of the near-catastrophe, the state assigned a six-person team of geologists and engineers to determine how we came so close to a heart-stopping disaster.

Today the panel released nearly 600-page report, and the verdict is nothing short of withering. According to the audit, decades of oversights, overconfidence, and even laziness resulting from a systemic and all-encompassing culture of error in state water resource management and regulation made the Oroville incident essentially inevitable sooner or later.

It’s a blistering review, and a profoundly worrisome one in a state with over 1,400 critical dam assets. Here are a few of the findings:

  • The panel blames state bodies for failing to pay attention to or properly fix the dam’s problems: “The Oroville Dam spillway incident was caused by a long-term systemic failure of the California Department of Water Resources (DWR), regulatory and general industry practices to recognize and address inherent spillway design and construction weaknesses, poor bedrock quality, and deteriorated service spillway chute conditions.”
  • The problems were longstanding, in place since day one: “The inherent vulnerability of the service spillway design and as-constructed conditions reflect lack of proper modification of the design to fit the site conditions. Almost immediately after construction, the concrete chute slab cracked above and along underdrain pipes, and high underdrain flows were observed.”
Spillway repairs in 2017.
California DWR
  • In fact, assets like the Oroville Dam were never as good as everyone presumed: “DWR has been significantly overconfident and complacent about the integrity of its infrastructure, including its dams. A contributing factor to DWR’s overconfidence and complacency was a somewhat widespread belief within DWR that the [State Water Project] was designed by the ‘best of the best’ – a belief passed on through two generations to the current generation, and possibly increasingly mythologized by each generation.”
  • Although the dam design was sufficient in a generic sense, it wasn’t suitable for the Oroville site: “While the Oroville design was within the range of design practices for rock foundations [...] it would not meet the typical practice of the day for spillway chutes on highly weathered or soil-like foundations. When conditions deviating from the design foundation conditions were encountered during construction, adjustments were not made.”
  • In fact, it looks like a lot of folks didn’t know much about the site at all: “The emergency spillway was designed with the intention that the crest structure would be founded on ‘good’ rock. [...] The thinking was that, if the emergency spillway operated, erosion would occur on the hillside, but the crest structure would not be threatened, and the reservoir would be retained. It appears that the expected erosion of the hillside was neither detailed nor quantified in the design documentation.”
  • And safety inspections frequently neglected problem spots: “In many of these inspections, the spillway chute was observed only from the deck of the spillway headgate structure. [...] The chute could not safely be inspected at close distance due to water on the gates, wetness of the chute surface, steepness of the chute, or other considerations. [...] There may have been an option to work with in-house DWR safety engineers to develop alternative methods to safely perform inspections under those conditions, but these options were not exercised.”
  • Frequent repairs might have made things worse: “It was not recognized that repairs which deteriorated in as little as few years after completion posed risks of increasing leakage into the foundations. [...] It also appears that it was not understood that development of deterioration of concrete in new areas, not just in previously repaired areas, was an indication of [...] likely continued degradation.”
  • Involved parties had plenty of opportunities to spot the problem before it became a near-disaster: “The incident was preceded by decades of somewhat complex interactions and effects of human and physical factors, through which numerous warning signs of the impending spillway failure were missed. [...] Overcoming so many barriers could be thought of as involving a degree of ‘bad luck,’ but more importantly, it indicates a long-term systemic failure of DWR, regulatory, and general industry practices.”
  • The problems are systemic, vastly encompassing, and not going away: “The incident cannot reasonably be blamed mainly on any one individual, group, or organization. [...] The fact that this incident happened to the owner of the tallest dam in the United States, under regulation of a federal agency, with repeated evaluation by reputable outside consultants, in a state with a leading dam safety regulatory program, is a wake-up call for everyone.”

You can read the full Independent Forensic Team Report on the Oroville Dam Spillway Incident here.

The Oroville Dam’s emergency spillway—little more than a dirt slope—in 2017, with a worker in a yellow hardhat standing at the brink of the hill and looking down at the valley below.
The emergency spillway—little more than a dirt hillside—in 2017.