SAN FRANCISCO (AP) — California released two reports by independent experts Monday on badly damaged flood-release spillways at the nation’s tallest dam after a surge in criticism that officials weren’t disclosing enough about risks from the damaged structures, and the rush to fix them.
State lawmakers, local officials and editorials in newspapers around the state last week urged California’s Department of Water Resources to make public the reports by government-appointed independent consultants and to be more forthcoming overall about the crippled spillways at the Oroville Dam.
“What we obviously need to do is get more public information out,” David Gutierrez, a former state dam safety official now serving as a consultant in the Oroville repairs told reporters Monday in announcing the reports’ release. State water officials also plan a series of public meetings on planned repairs so that people “understand the concepts, and that we will actually fix the spillway,” Gutierrez said.
Authorities ordered the evacuation of nearly 200,000 people downstream on Feb. 12 after the first and then the second spillway at the 770-foot dam had begun ripping away amid a record-wet winter, threatening to flood towns downstream. Authorities allowed residents to return within days, and there were no reported deaths.
In the two reports released Monday, the four appointed consultants pointed to cracks in the concrete as a likely cause of the failure of the main spillway. Water entering through the cracks may have gouged large holes under the concrete, and then lifted off the large slabs torn from the concrete, the experts said. The last reported repairs to cracks in the half-century-old spillway were in 2009, the experts noted.
Water agency spokeswoman Erin Mellon said Monday the experts’ preliminary finding on the cause of the crisis was speculative. A separate team of experts is charged with pinpointing the causes of the spillway failures and examining how officials handled the crisis.
California is rushing to carry out hundreds of millions of dollars in repairs to have the main spillway operational again by Nov. 1, around the start of the state’s rainy season.
Monday’s reports also show the independent experts urging that state officials tear out and completely replace at least the upper stretch of the damaged main spillway this summer, rather than trying to simply repair it. State officials said they agree.
Work crews, due to start work in May, are expected to run out of time to fix the lower part of the main spillway this year. If that’s the case, state officials said Monday they may divert water releases down the hillside next to the cratered main spillway.
A federal dam agency that oversees large hydroelectric dams such as Oroville last month released the first of the three known reports by independent consultants. The experts described the spillway as In worse shape than state officials had described. The experts spoke urgently of the risk to the public if the main spillway were not operational by the next rainy season.
The water agency, the dam’s operator, then asked for and got subsequent reports withheld from public review, citing federal law meant to minimize the risk of terror attacks on critical infrastructure.
As public objections built, acting state water agency chief William Croyle said earlier this month the agency might release the reports with redactions. The reports released Monday appeared largely intact, with short redactions apparently addressing specific physical vulnerabilities of the spillways.
The independent experts in the two newly released reports also urged the state to consider replacing the damaged backup flood-release spillway with a full, concrete chute with floodgates. Conservation groups had urged the state since at least 2005 to strengthen the emergency spillway, which featured a concrete lip but otherwise was designed to send water rushing down a bare hillside. It was the breakup of that emergency spillway, threatening uncontrolled releases of massive amounts of water, that ultimately led to the Feb. 12 evacuation order.