PALM SPRINGS, Calif. — In 2005, three environmental groups raised concerns that the emergency spillway at California’s Oroville Dam wasn’t properly built and posed serious risks.
The groups — Friends of the River, Sierra Club and the South Yuba River Citizen’s League — described their worries in a motion to the Federal Energy Regulatory Commission, which was considering the dam’s relicensing.
The environmentalists wanted federal officials to require modifications including building a concrete-armored spillway rather than leaving it a concrete “lip” above an unprotected hillside prone to erosion damage. They warned that given the spillway’s design, possible uncontrolled floodwaters “could not only cause additional damage to project lands and facilities but also cause damages and threaten lives in the protected floodplain downstream.”
State officials who manage the dam dismissed those concerns at the time, and federal regulators are still considering the license renewal. But the warnings aired more than a decade ago have turned out to be well-founded, as officials have ordered entire towns evacuated and Gov. Jerry Brown has declared an emergency.
Ron Stork, a senior policy advocate with Friends of the River, said the current emergency is precisely what he had feared.
“Our combined judgment at the time was that the Oroville Dam complex could not be used safely or confidently to conduct flood control operations,” Stork said in an interview Monday. He said the environmental groups had demanded “a proper spillway.”
“There isn’t one. It’s a spillway lip, a little bump on the top of a hill,” Stork said, explaining that having the bare hillside below the emergency spillway allows for major erosion damage to the hillside when water pours over as it did on Sunday.
Photos: Thousands evacuated near Oroville Dam in Calif.
At 770 feet high, the dam is the tallest in the country. It’s also California’s second-largest dam in volume and the largest in the State Water Project, a network of canals and pumping stations that move water from Northern California to the Central Valley and Southern California. It’s one of the key reservoirs in the system that stores water for the dry spring and summer months.
Building a concrete-armored spillway would have required water districts that rely on the State Water Project to absorb some increases in the costs of water, and Stork said they didn’t want to do that at the time.
“They didn’t want to pay for a second spillway, which almost failed last night,” Stork said. And as for state regulators, he said, “what they said is that the existing spillway is safe.”
The environmental groups’ warnings about the dam’s emergency spillway were first reported by the San Jose Mercury News.
Oroville Dam, located in the foothills of the Sierra Nevada east of the Sacramento Valley, was completed in 1968.
The reservoir rose rapidly this winter as the Feather River and its tributaries gushed down swollen after heavy rain and snow. The storms, which came after more than five years of severe drought, have led officials to release water from various dams across Northern California.
A gaping hole appeared in Oroville Dam’s main spillway last week, and then water began pouring over the emergency spillway for the first time in the reservoir’s history.
While the dam itself remained intact, erosion damage to the emergency spillway over the weekend raised the potential of the structure failing and unleashing a dangerous torrent of floodwaters.
Trying to head off a disaster, state officials increased the flow down the main spillway on Sunday night, and on Monday the lake’s level was dropping. Oroville and other communities downstream remained under evacuation orders due to the threat of flooding.
Officials said they hoped their increased use of the main spillway would save the emergency backup chute, and that efforts to fill holes in the auxiliary spillway with bags of rocks could shore it up. The National Guard sent helicopters to assist with the emergency reconstruction effort.
More storms are headed for California this week, and forecasters say they will be strong enough to bring 2 to 6 inches of rain to Oroville.
Michael Dettinger, a hydrologist with the U.S. Geological Survey, said the coming storms plus the heavy snowpack in the mountains above the reservoir make for an emergency that won’t ease anytime soon.
“The real tension now comes from the fact that we still have as much as another 6 weeks’ worth of on-again-off-again storminess … before we are likely to be able to breathe calmly about the kind of situation we saw at Oroville this weekend,” Dettinger said. “That’s a lot of opportunities for another big storm or storm sequence to show up, and all the outlets at Oroville are pretty much limping at this point.”
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