OROVILLE — A 19-month study of the safety of the Oroville Dam project has found no “unacceptable risks.”
The Department of Water Resources released its Comprehensive Needs Assessment on Oct. 30, and notes its findings generally agree with those of an Independent Review Board and a regular five-year review by the Federal Energy Regulatory Commission that was completed in July.
Though no unacceptable risks were found, several “potential vulnerabilities” were identified. DWR said work is underway to address some of those.
“Public safety is at the core of DWR’s mission, and we are committed to continually evaluating the performance and safety of State Water Project facilities, including Oroville Dam,” DWR Director Karla Nemeth said in a press release.
“The Comprehensive Needs Assessment report is an important step in our efforts to ensure the ongoing safety and reliability of facilities that provide water and flood control for millions of Californians.”
Butte County Supervisor Bill Connelly is less impressed with the work. “I think in their minds it’s the best, most professional report ever and they think everything’s good. And that scares me.”
“It’s the same mindset that caused the spillway crisis.”
The study
The safety study stems from the February 2017 breakup of the main spillway, and subsequent rapid erosion of the emergency spillway, risking its collapse. That prompted evacuation orders affecting 188,000 people downstream along the Feather River.
In the aftermath, DWR committed to federal and state authorities that it would do the comprehensive safety study. Work started in January 2018, and was completed this August.
In the interim, DWR contractor Kiewit Infrastructure West rebuilt the main spillway over the course of two summers of work. The dike at the head of the emergency spillway was armored, and a large concrete splash pad was built beneath the dike, stretching downhill to an erosion-blocking wall drilled into bedrock.
The group working on the safety study was divided into six engineering teams and one oversight team managing the work and checking the findings. The Independent Review Board also reviewed the findings, and made 97 recommendations for changes.
There was also a group of locals meeting regularly with those working on the report to make sure community interests were kept in mind. That group included Congressman Doug LaMalfa, state Senator Jim Nielsen, Assemblyman James Gallagher, Supervisor Connelly and Sheriff Kory Honea, among others.
Each of the six engineering groups looked at a different aspect of the dam complex. For example one studied the dam itself, while another looked at dam operations.
The groups were looking for “potential failure modes” where some aspect of the facility could either fail completely, suffer heavy damage or minor damage.
Initially they identified 367 of the “PFMs.” That was culled down to 129, with more than 400 scenarios. More than 2,000 risk evaluations were done which combined the likelihood of the failure with the consequences downstream.
That was the math that determined there were no unacceptable risks.
Projects
Some work has been done to address the potential liabilities that were found.
Thus far 12 new monitors to measure water pressure and level have been installed in the dam and around the main spillway floodgates. Approval is being sought for installation of five more of the devices — piezometers — in the dam to measure seepage.
Preliminary steps have also been taken toward a seismic study of the stability of the dam in the event of a major earthquake.
DWR has also committed to three other projects “in the near term.”
They include raising the Parish Camp Saddle Dam by 3 feet. The study found the small dam, on the south side of the Lime Saddle Recreation Area, could be overtopped in the event of a huge storm and cause damage downstream.
Lining of the Palermo Canal is also called for. The canal, fed by a tunnel through the south side of dam, runs upslope from the Hyatt Powerplant. Lining the canal would reduce the potential of a landslide that could knock the powerplant out, limiting DWR’s ability to control water levels in the lake.
The third project is adding a redundant power system for operation of the gates at the top of the main spillway to eliminate the need for external power.
DWR is also moving toward a forecast-based operations manual for the dam. Weather approaching Northern California would determine how high the lake should be, in coordination with the dams operated by the federal government and Yuba County.
It would replace a flood control manual dating to the 1960s that assumed another dam would be built in the Feather River at Marysville.
A number of other projects have been recommended, but the report says in several places that any work that is done will have to be cost-effective, compared to projects to reduce risks at other State Water Project facilities.
“Since there are no unacceptable risks at Oroville,” the report states, “DWR will need to make balanced risk-informed decisions regarding where the highest risks are within the SWP, and to then set the priorities to reduce those risks across the entire SWP.”
“It’s the fox guarding the henhouse again,” Connelly said. “They say there’s chance an earthquake could cause a landslide that would knock the powerhouse out, but it’s not a problem because there’s only a 1-in-500 chance it would happen.
“I can’t build a house that way. I can’t ignore an earthquake threat because there’s only a 1-in-500 chance it will happen.”
Assemblyman Gallagher calls the report “a step in the right direction,” but is also concerned about a lack of commitment to sustained funding for potential projects that have been identified.
He said a number of positives have come out of the process, citing the placement of the piezometers and a study that found good rock beneath the spillway gates.
But he wanted to see “more of a funding commitment dedicated to the long-term safety of the dam.”
“We want to continue to see that funding investment because we’ve all seen that when things go wrong, it’s far more expensive.”
Ahead
Potential vulnerabilities identified by the study included scenarios that could flood the Hyatt Powerhouse and possibilities that would prevent operation of the floodgates at the top of the main spillway.
An unprecedented storm could result in water flowing over the main dam, at the saddle dams at Bidwell Canyon and Parish Camp, possibly breeching one of them.
The possibility of erosion of the dam itself was also raised, particularly where it joins the main spillway.
It turns out the dam is higher than its abutments. The report said adding parapet walls there and along the top of the dam would reduce the risk. The report says this would be a cost-effective step, and recommends it in the “near-term” interim phase. The interim phase is elsewhere described as being over the next five years.
There are also 22 large-scale, long term potential projects listed that would reduce risk. They include building a second concrete spillway, and adding a second set of gates upstream from the gates on the existing main spillway.
The 22 projects are grouped into 10 different plans, estimated to cost between $500 million and $3.7 billion.
Gallagher said the local leaders pressed unsuccessfully for commitment to build a second outlet tunnel under the dam.
Currently water is most often released through the powerhouse, which can move 14,700 cubic feet per second. There is also a direct tunnel from the lake to the diversion pool, called the river valve. However it can only move 4,000 cfs. If more water needs to be released than that, the spillway comes into use.
Gallagher said a second tunnel would provide more flexibility, but thus far hasn’t been able to convince DWR.
Still, he thinks local views are being listened to. He and other representatives from the area sit on a new commission that provides a “long-term forum” on dam issues. He said no one is taking what DWR is saying at face value, and there has been a lot of “pushback.”
“We’re not getting everything we want, but we’re not going away.”
