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Officials seek to quell doubts about Oroville Dam’s future safety

State officials say patches of green foliage on the face of the Oroville Dam aren’t the result of seepage, but University of California experts say they aren’t so sure.
Tim Hearden

Capital Press

Published on September 5, 2017 3:14PM

California Department of Water Resources workers inspect the face of the Oroville Dam on Aug. 10, finding the vegetation brown and dry from the hot summer. A state report concludes that patches of green grass that occasionally appear on the earthen dam are the result of puddling from rain and not seepage from the dam.

Calif. Department of Water Resources

California Department of Water Resources workers inspect the face of the Oroville Dam on Aug. 10, finding the vegetation brown and dry from the hot summer. A state report concludes that patches of green grass that occasionally appear on the earthen dam are the result of puddling from rain and not seepage from the dam.

Patches of green vegetation are seen on the face of the Oroville Dam in March 2011. A state report concludes that the green patches that occasionally appear on the earthen dam are the result of puddling from rain and not of seepage from Lake Oroville.

Calif. Department of Water Resources

Patches of green vegetation are seen on the face of the Oroville Dam in March 2011. A state report concludes that the green patches that occasionally appear on the earthen dam are the result of puddling from rain and not of seepage from Lake Oroville.


OROVILLE, Calif. — State officials are assuring the public that Oroville Dam will be safe in the future despite the lingering doubts of University of California experts about its integrity.

Department of Water Resources officials have concluded that a patch of green grass that often appears on the face of the dam is the result of puddling from rain and not caused by seepage from the lake.

An independent Board of Consultants convened to help guide the dam’s reconstruction in the wake of its spillway failure in February agreed with the department’s findings, said Erin Mellon, the DWR’s assistant director of public affairs.

“The vegetation area poses no threat to the integrity of the dam,” Mellon said in an email, adding that it was observed during the dam’s construction in 1966 and 1967, before the lake was filled. “The area is caused by temporarily trapped rainwater.”

But a pair of University of California-Berkeley infrastructure risk management experts say they aren’t yet convinced. A team led by Robert Bea and Tony Johnson of the university’s Center for Catastrophic Risk Management warned in a July report that the green foliage could be an indication of a leak or leaks in the earthen structure.

The report detailed a series of clues to possible leaks, such as persistent wet spots around the dam and needed patchwork repairs. It called for state agencies and the Federal Energy Regulatory Commission to do “high-quality field investigations” and analyses to determine if seepage is occurring.

Bea told the Capital Press the DWR appears to have simply analyzed previous data and repackaged it, repeating mistakes that caused the agency to overlook the risks that led to the February spillway crisis.

“Our knowledge and experience indicates it is much better to be safe than sorry when the stakes … are high,” Bea said in an email. “We are not concerned with the equivalent of a leak or leaks in a garden water bucket. We are concerned with the equivalent of a leak or leak in a nuclear power plant containment vessel.”

Mellon responded the state’s “study speaks for itself.” She said ongoing seepage measurements at the base of the dam have remained consistently low and virtually unchanged since construction of the dam.

The vegetation area dries out during the summer, which it wouldn’t do if it had constant seepage through the dam, she said.

“The vegetation area is currently brown and dry despite the … lake level sitting almost 100 feet higher than the vegetation area,” Mellon said.

The discord comes as the state is increasing scrutiny of some of its dams in the aftermath of the Oroville crisis, which led to the evacuation of about 188,000 area residents and threatened a large portion of the Eastern Sacramento Valley’s $1.5 billion agriculture industry.

Crews are in the midst of a $275.4 million repair and reconstruction project at the dam, as the first phase of work on the main spillway is slated to be completed by Nov. 1.

The dam had a satisfactory rating from the state Division of Safety of Dams before its near-failure, and “there was nothing in state or federal analyses” of the dam that suggested it didn’t deserve the rating before last winter’s emergency, Mellon said.

The dam’s condition is now rated as unsatisfactory, which it will remain until refurbishments are complete, said Sharon Tapia, chief of the dam safety division.

The emergency led the division this spring to order re-evaluations of 93 dams with spillways similar to Lake Oroville’s, which are now ongoing. Several of the dams create major reservoirs, including the Don Pedro Dam on the Tuolumne River, the New Bullards Bar Dam on the Yuba River, the New Exchequer Dam on the Merced River and the Pine Flat Dam on the Kings River.

The agency wants a new look at spillways that are very steep, as is Oroville’s, or serve dams on softer rock that are more prone to eroding, Tapia said.

“We were looking at a lot of dams in the foothills and along coastal ranges,” she said.

Owners of the dams were required to submit work plans and investigate conditions of their spillways. Re-evaluations are more than just simple inspections; they often involve field research and can take several years to complete and cost millions of dollars, Tapia said.

“The dam owners are being very responsive to this requirement,” she said.



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