Oroville Dam spillway: 'It's not supposed to do that'
The forensic team investigating the February emergency at Oroville Dam blasted the California Department of Water Resources on Friday, saying the dam’s owner and operator did a poor job of designing, building and maintaining the structure and neglected safety while focusing on the “water delivery needs” of its customers to the south.
Citing a “long-term systemic failure” by both DWR and federal regulators, the group of independent investigators released its final report Friday on the nearly catastrophic fracture in the dam’s main flood-control spillway in early February, which eventually forced the evacuation of 188,000 downstream residents.
The 584-page dissection of the near disaster at America’s tallest dam found that the structure was designed and built with flaws dating to the early 1960s, when an inexperienced designer was put in charge of overseeing the development of the facility’s two spillways. Design flaws were exacerbated by inadequate repairs in the years that followed, making the crisis inevitable.
“Due to the unrecognized inherent vulnerability of the design and as-constructed conditions and the chute slab deterioration, the spillway chute slab failure, although inevitable, was unexpected,” the report said.
Hired at the direction of the U.S. government, the panel said DWR put “insufficient priority on dam safety” and focused too much energy on delivering water to the agencies that belong to the State Water Project. The water stored at Oroville is delivered to millions of Californians, including customers of the mammoth Metropolitan Water District of Southern California, and irrigates 750,000 acres of farmland.
The panel also said the governor’s office and the state water contractors – the member agencies of the State Water Project – likely put pressure on DWR to rein in costs.
John France, the forensic team’s leader, said he understands how hard it is to balance competing interests, “but we believe dam safety as it sits now needs a bit higher profile.” The panel complained that there isn’t a single senior official at DWR who is responsible for dam safety in California.
For some Oroville residents, the report was grim vindication of a long-held belief that DWR cares more about the water demands of far away cities and farms than it does for the well-being of the people below the dam.
“It’s ingrained, it’s normal to overlook things, and to keep the cost down and deliver the water,” said Butte County Supervisor Bill Connelly. “That’s how they treat us.”
Metropolitan General Manager Jeff Kightlinger denied any suggestions that cash concerns compromise safety.
“We know we end up having to pay the lion’s share of repairs if something breaks – and it’s our water supply,” he said. “We’ve always pushed them to be more aggressive in maintaining, not less.”
The crisis began when a crater opened in the main flood-control spillway Feb. 7. The investigative team criticized DWR’s initial handling of the problem, saying it shouldn’t have allowed water to pour out of the adjacent emergency spillway. Problems at the emergency spillway forced the evacuation of 188,000 downstream residents.
Investigators also said federal regulators and leaders of the dam-safety community must heed the lessons of Oroville, too.
“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 involved in dam safety,” the panel wrote.
The six-member investigative team said there was “no single root cause” for the crisis. Rather, the panel pointed to a “complex interaction of relatively common physical, human, organizational and industry factors.”
France said the Federal Energy Regulatory Commission, which licenses the dam and oversees an in-depth inspection at Oroville every five years, needs to re-examine how it regulates dam safety. FERC’s most recent inspection in 2014 said a failure of the flood-control spillway was so unlikely that there was no need to plan for such an emergency.
But officials in the Oroville area said the lion’s share of the blame belongs with DWR. “This happened at a dam that DWR operates,” said Assemblyman James Gallagher, R-Yuba City. “That’s ground zero. That’s where you’ve got to start.”
Problems at Oroville began during design work in the 1960s. The principal designer of both spillways was hired from a university post-graduate program and had “no prior professional experience designing spillways,” according to the report. The investigative team “finds it striking that such an inexperienced engineer was given the responsibility of designing the spillways of what is still the tallest dam in the US.”
The designer, who wasn’t identified by name, also failed to communicate properly with geologists working on the project and was led to believe the spillway would be built on “good quality rock,” the report said. That turned out to be a deeply flawed assumption.
Soon after the dam was completed in 1968, the 3,000-foot-long concrete chute cracked above and along underdrain pipes, leading to higher-than-expected flows of water directly beneath the structure.
“The slab cracking and underdrain flows, although originally thought of as unusual, were quickly deemed to be ‘normal,’ and as simply requiring on-going repairs,” the panel wrote. “However, repeated repairs were ineffective and possibly detrimental. ... These repairs did not successfully address the root causes of the observed deterioration, were not well suited to resist high velocity (water) flows, and were generally short-lived, typically beginning to deteriorate (within) a year or two after completion.”
The spillway had other problems. Its steel rebar corroded, as did the anchors that were supposed to secure the concrete to the underlying bedrock. The bedrock itself was plagued by “erodible materials” that were left in place during construction. Many of these “poor foundation conditions” beneath the concrete were documented in geological reports but weren’t properly addressed during design and construction, the panel concluded.
All these factors came together Feb. 7, as the dam was releasing water down the spillway to lower reservoir levels during a massive rainstorm. Water that had crept into the cracks and joints of the concrete chute resulted in “uplift forces beneath the slab,” causing the spillway to erupt.
Jeffrey Mount, a geologist and water expert at the Public Policy Institute of California, said the forensic report underscores how a series of seemingly small problems can add up to a major crisis. “It’s never just one thing,” said Mount, who wasn’t part of the forensic team. “Events like this are a cascade of things. ... They did a good job of showing how institutions normalize problems: ‘We can live with this, we can patch it, it will be just fine.’”
After the crater formed on the main spillway, dam operators decided to curtail water releases on the chute the next few days to limit the damage. Water levels at Lake Oroville, the state’s second largest reservoir, rose so high that water started pouring over the nearby emergency spillway, which consists of a concrete lip sitting on an unlined hillside, for the first time since the dam opened.
The hillside eroded so badly that dam officials feared the lip of the emergency spillway would crumble, releasing a “wall of water.” Downstream communities were evacuated until lake levels subsided and water stopped pouring over the emergency spillway.
The forensic team said the DWR dam operators should have understood how risky it was to use the emergency spillway.
“The decisions were made with the best of intentions, but against the advice of civil engineering and geological personnel, who had by then recognized the poor bedrock conditions and the potential for unsatisfactory performance of the previously untested emergency spillway,” the team wrote. France said reports from the early 1960s cited the bedrock’s flaws, but those warnings were forgotten in the ensuing decades.
France said the forensic team wasn’t trying to be overly critical of how DWR responded to the initial emergency. “We’re not trying to second-guess the decision; we’re trying to learn from it, for the future,” he said. “I can envision being in that situation and weighing one of those risks more than the other.”
The panel also called DWR a “somewhat insular organization” that hasn’t tapped “industry knowledge” sufficiently. “Like many other large dam owners, DWR has been somewhat overconfident and complacent regarding the integrity of its civil infrastructure.”
All told, France said DWR is “in sort of the middle of the pack ... in dam safety practices.”
That’s a blow for an agency that had built a reputation for diligently policing California’s dams. An audit in 2016 by the Association of State Dam Safety Officials concluded that California operates “the leading dam safety program in the nation.” Yet a Sacramento Bee investigation last fall showed that dam owners have been allowed to let flaws and deficiencies go unrepaired for years, even after repeated notifications from DWR’s inspectors.
State officials said they incorporated the forensic team’s preliminary findings, released in May and September, into the massive repairs that began last spring.
DWR Director Grant Davis, in a prepared statement, said “we will carefully assess this report, share it with the entire dam safety community and incorporate the lessons learned going forward to ensure California continues to lead the nation on dam safety.” Davis joined DWR last fall.
The flood control spillway has been largely repaired, although portions are awaiting further repairs later in 2018.
The total emergency is expected to cost $600 million or more. State officials expect the federal government to cover most of the cost, with leftover expenses to be shouldered by Metropolitan and other members of the State Water Project.