OROVILLE — Despite increased maintenance of Oroville Dam since the spillway fell apart in February 2017, members of the community-led Oroville Dam Ad Hoc Group have expressed concern about the age and wear of mechanics within the spillway’s main gates, citing similar failures on dams of the same era.
The Department of Water Resources convened a meeting Nov. 13 of the Oroville Dam Ad Hoc Group — an organization comprised of local elected officials and stakeholders appointed by state Sen. Jim Nielsen (R-Tehama) and Assemblyman James Gallagher (R-Yuba City) — as part of the Oroville Dam Safety Comprehensive Needs Assessment that was initiated by the DWR after the spillway crumbled.
The eight, extremely large gates at the top of the spillway are controlled by a mechanism known as a Tainter gate. The radial-style gates are commonly used on dams and canal locks across the world because the water flow under that type of gate assists in opening and closing the gate. They resemble a piece of pie with the curved side against the flow of water. But after many decades of use, that style of gate can put an extreme amount of stress on the pins holding the moving arms in place.
The Oroville Dam was built in 1968, more than 50 years ago, and the gate mechanism was never meant to be replaced. Of particular concern are the anchor tendons on each gate — there are 24 on each side, buried in concrete, dozens of feet deep in the towering columns on either side of the gates.
That means they’re impossible to get to, or even to observe, for an accurate picture of their functionality, said Chris Souder, Chico State professor and chair of the university’s construction management department. Souder is not in the Ad Hoc Group.
Robert Bea and Tony Johnson of the UC Berkeley Center for Catastrophic Risk Management, said in an independent study in 2017 they have proof that two out of 384 anchor tendons have already failed and they believe DWR is aware of 28 more that have “crack indicators” in the steel.
There is no non-destructive way to look at the tendons and see what condition they’re in, said DWR representatives at the Nov. 13 meeting.
Therefore, the department must look to build in redundancies — not replacements — into the dam operation, such as creating a second spillway site or another gate system in front of the existing gates, capable of the same amount of water flow.
Engineers would “have to block the lake on the upstream side in order to take a gate out of commission for repair or replacement,” Souder said.
This sort of issue is exactly why Gallagher and Neilsen pushed for the public to have a seat at the table, the assemblyman said.
“That’s what we were missing for many years,” Gallagher added. “They haven’t said the gates are deficient right now, or that there’s anything right at this moment that is going to fail, but it is older.”
“It’s 50 years old,” Gallagher said. “I favor looking at what we have to do to replace it completely.”
But DWR officials — and Souder’s professional view — is that complete replacement is absolutely not an option.
Similar dams, similar problems
Part of the problem is that dams from the mid-20th century simply do not have the same regulations that modern dams do.
Folsom Dam, on the American River in Folsom, was built in 1955 and had a serious problem with its No. 3 gate in 1995. A 35-inch trunnion pin — integral to the system of opening and closing the radial gate arms — snapped due to excessive friction and corrosion over time.
The gate was stuck open and about 40 percent of the storage in Folsom Lake was lost. Thankfully, there was no damage to the rest of the dam operation and no lives were lost in the increased pour downstream thanks to quick actions by officials there. The gates were repaired by the U.S. Bureau of Reclamation at a cost of about $20 million in 1995 — that’s approximately $34 million today.
The Poe Dam, upstream of Lake Oroville on the Feather River, was retrofitted in 2017, when PG&E commissioned some testing to determine the structural integrity of the aging radial gates.
The results indicated excess friction in the trunnions — similar to what caused the problem at Folsom Dam — and overstressing of the gate arms. PG&E elected to replace the gate end arms and trunnion assemblies.
Souder said he toured the Poe Dam while this was going on two years ago.
“(PG&E) put large steel bulkhead plates to block the river in each bay while they replaced the anchors and repainted the gates,” he said.
A similar set up could be used to repair each gate individually on the Oroville Dam should DWR choose to do so.
DWR aware but not concerned
“The spillway gate structure, as well as the radial gates anchor rod condition and performance, have been regularly assessed by DWR engineers, state and federal regulators, including the U.S. Army Corps of Engineers and independent experts using a variety of non-destructive industry-tested methods,” said DWR Oroville Public Information Officer Liza Whitmore in a statement. “These tests have determined no current issues. Additionally, the gate’s operational capability continues to pass a yearly certification process.”
The Department of Water Resources has tried many different non-destructive testing techniques to evaluate the condition of some of these anchors with varying results, said Steve Verigin at the Ad Hoc Group meeting. Verigin is a senior vice president and senior consulting geotechnical engineer with consulting firm, GEI, and was previously the chief of the Division of Safety of Dams, deputy director and acting chief deputy director at DWR.
“(DWR has) taken steps in the operation and maintenance of the structure to protect some of these anchors that are in place,” he said.
Verigin said he did not believe it was a viable solution to try to drill new anchors into the piers, but that there may be an opportunity to deploy new bulkhead gates upstream of the existing radial gates.
“While you wouldn’t prevent the loss of one of those (radial) gates, the likelihood of … losing a gate through successive failure of multiple anchors might be low enough that you might be satisfied with the provision of putting in new bulkhead gates,” he told the Ad Hoc Group. “We’re not finished with this one. We have to work on these measures to satisfy the concerns of those different loading conditions.”
But perhaps Genoa Widener, a private citizen of Oroville and the administrator of the Facebook group, “Not Just A Spillway,” put it best at the Nov. 13 meeting: “It just doesn’t make sense to me to have this brand-new state-of-the-art spillway with these old, cracked, decaying gates on top of it.”
