Water officials ramp down Oroville spillway
Federal regulators are re-evaluating how they conduct dam inspections following the Oroville Dam spillway crisis, and they’ve ordered the nation’s dam operators to thoroughly inspect their facilities to see “if they have a potential Oroville waiting to happen,” a federal inspector said Sunday.
“Can we make things different? Can we improve things?” said Frank Blackett, a regional engineer at the Federal Energy Regulatory Commission’s Division of Dam Safety and Inspections.
Speaking at an American Society of Civil Engineers conference in Sacramento, Blackett listed the array of state and federal inspectors who visited Oroville Dam over the years. All of them, he said, missed signs that could have foreshadowed the gaping crater forming in the dam’s concrete spillway in early February, eventually leading to the frantic evacuation of 188,000 people.
“One thing we (the inspectors) all have in common is that we didn’t predict this happening,” Blackett said.
Since the crisis, Blackett said, FERC has sent letters to the nation’s dam operators ordering them to conduct thorough on-site inspections of their spillways, re-evaluate their construction and design plans, and try to envision scenarios to determine “how that structure could fail.”
“We want all of our licensees to focus on these features and determine if they have a potential Oroville waiting to happen,” Blackett said.
Inside FERC, he said, the agency has hired consultants to perform an internal audit “to look at the way we do inspections, the way we run our program.”
A California Department of Water Resources official on the same panel as Blackett also noted that inspections conducted over the years failed to predict the spillway failure.
In 2014, an inspection “actually dismissed the plausibility” of failures arising from erosion at the emergency spillway “or a failure of the concrete chute” in the main spillway, said Mark Andersen, an acting DWR deputy director.
“So clearly ... we need to look institutionally at how we are doing these inspections and what we’re learning from them,” Andersen said.
Earlier this month, FERC asked Pacific Gas and Electric Co. to perform inspections on 33 spillways the power company oversees and compile a report on the state of their spillways by the end of the year, said PG&E spokesman Paul Moreno. The largest of the PG&E dams is on Lake Almanor, a reservoir whose releases drain into the same Feather River watershed as Oroville. Almanor is about one-third the size of Oroville.
On the Yuba River, which drains into the Feather below Oroville Dam, FERC inspectors are meeting this week with the operators of New Bullards Bar Dam for an annual inspection, said Curt Aikens, the general manager of the Yuba County Water Agency. New Bullards Bar is slightly smaller than Folsom Lake.
After the Oroville crisis, the agency proactively also hired an engineering firm to do a complete and in-depth spillway inspection, which Aiken said includes high-tech “ground penetrating radar, echo impact testing along with video inspection of the drains.”
“My understanding is that these advanced technologies can identify spillway slab thickness, rebar location and potential defects in the spillway,” Aikens said.
Other dam operators around California said they’re awaiting instructions from FERC on how to overhaul the inspection process.
“If they change or propose new inspection guidelines, we’ll follow those criteria,” said Calvin Curtin of the Turlock Irrigation District, which manages New Don Pedro Dam on the Tuolumne River in the San Joaquin Valley. “We would obviously cooperate.”
New Don Pedro, built in 1967, is California’s sixth largest reservoir, capable of storing 2.03 million acre-feet of water.
The U.S. Bureau of Reclamation, which operates Shasta, Folsom and many other large California dams, hasn’t received any new guidance from FERC, said bureau spokesman Louis Moore.
Blackett’s remarks in Sacramento represent one of the few public statements FERC has made since the Oroville crisis erupted. FERC licenses Oroville Dam, which is operated by the state Department of Water Resources.
A massive sinkhole formed in Oroville’s main spillway on Feb. 7 during heavy storms. Lake Oroville rapidly filled and water started flowing over the adjacent emergency spillway – a concrete lip above an unlined hillside – for the first time in the dam’s history.
The hillside eroded badly, prompting fears that the emergency spillway would crumble and release a “wall of water.” That triggered the two-day emergency evacuation of 188,000 residents downstream on Feb. 12. The crisis, including an ongoing two-year repair plan, is estimated to cost $550 million.