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A race against Mother Nature as officials send water cascading out of Lake Oroville

With more storms expected to slam Northern California later this week, officials worked frantically Monday to drain water from brimming Lake Oroville in hopes of heading off a potentially catastrophic flood.

The operators at America’s tallest dam found themselves in a precarious position Monday, with both of the spillways used to release water compromised and the reservoir still filled almost to capacity after a winter of record rain and snow. Meanwhile, tens of thousands of evacuated residents downstream of the dam still have no clear word when they can return home.

Officials sent millions of gallons of water per minute down the massive reservoir’s main spillway. Engineers said that despite a huge gash that opened in the concrete channel a week ago, it was their best option for lowering the dangerously high lake level.

They hoped this would avert further use of the emergency spillway, where damage was discovered Sunday afternoon.

“It was the lesser of two evils,” state Department of Water Resources spokesman Eric See said Monday. “We didn't want to have more damage, but we needed to evacuate water.”

The emergency spillway suffered severe erosion the day after water cascaded down the unpaved hillside for the first time since the dam opened in 1968.

The damage occurred even though the spillway was designed to handle much more water than the amount that overflowed. Some questioned why officials didn’t heed suggestions more than a decade ago to fortify the emergency spillway.

When it appeared the erosion could quickly worsen Sunday afternoon and potentially undermine the spillway’s concrete lip  — a scenario that could unleash a massive wall of water — officials ordered more than 100,000 people to evacuate the low-lying areas along the Feather River.

Racing against Mother Nature, water resources officials Monday sent water surging down the concrete main spillway -- a move that lowered the lake level by several feet but threatened to widen the gash. Erosion on the main spillway so far was manageable, See said.

“I’ve been doing these flood battles since 1978,” said state Sen. Jim Nielsen (R-Gerber). “This is the one with the greatest potential for damage of all the ones I’ve dealt with.” 

Both spillways are separate from the Oroville Dam itself, which officials say is not in danger of collapsing.

Officials said they want to lower the lake 50 feet by Wednesday to avoid another overflow on the damaged emergency spillway. If the head of the spillway crumbles, a 30-foot wall of water could go crashing down the hillside into the Feather River and toward Oroville, Marysville and Yuba City.

“Obviously any rain this week is not helpful at all,” said Tom Dang, a National Weather Service meteorologist in Sacramento.

On Monday, geysers of water shot from the placid lake and down the concrete spillway, like a water slide the width of a freeway.

Live updates from Lake Oroville »

Helicopters flew overhead and dump trucks shuttled across the top of Oroville Dam, carrying loads of rock to fill the eroded section. Without reinforcements, water could creep beneath the lip, causing it to crumble and allowing water to gush over the side.

In a letter Monday, Gov. Jerry Brown asked the Trump administration for a federal disaster declaration, saying the problems were likely to be more than local and state officials can handle.

Brown told reporters that he spoke to a member of the president’s Cabinet on Monday, but declined to say which one. “My office has been in touch with the White House,” Brown said. “I think that will be sufficient.” 

The Federal Emergency Management Agency, meanwhile, sent an eight-person team to the area to help California officials prepare for potential flooding.

“We are trying to plan for the worst-case scenario,” said Ahsha Tribble, acting regional administrator for FEMA’s Region 9, which includes California. “It’s not a wait-and-see game.”

Lake Oroville is the keystone of the State Water Project, which sends Northern California water hundreds of miles south to the southern San Joaquin Valley and the Southland.

During much of the five-year drought, the lake level was far below normal, forcing officials to slash water deliveries. But an extraordinarily wet winter filled the lake so close to capacity that officials have been forced to release water to prevent flooding.  

A series of powerful storms Tuesday sent runoff rushing into the reservoir, just as the hole appeared in the main spillway. Managers slowed the release of the water, and on Saturday, Oroville overflowed.

Earth and weak rock near the top of the spillway started to erode, when peak flows were 12,600 cubic feet per second, compared with the designed capacity of 450,000 cubic feet per second, according to the Department of Water Resources. The erosion happened so quickly that officials feared the concrete wall would be undermined and ordered sweeping evacuations in Butte, Yuba and Sutter counties that remained in effect Monday night.

Bill Croyle, the acting director of the Department of Water Resources, said Monday that he was “not sure anything went wrong. This was a new, never-happened-before event."

But during 2005 relicensing proceedings for Oroville Dam, several environmental groups argued that substantial erosion would occur on the hillside in the event of a significant emergency spill. In a filing, they asked the Federal Energy Regulatory Commission to order the state to “to armor or otherwise reconstruct the ungated spillway.”

State Water Project contractors, including the Metropolitan Water District of Southern California, were involved in the relicensing. MWD General Manager Jeffrey Kightlinger said Monday his agency deferred to the state and federal agencies on the matter.

“They did look at that issue and they determined that [the existing emergency spillway] did meet the appropriate FERC guidelines,” Kightlinger said. “In the FERC guidelines, they talk about how you don’t put a lot of funding and concrete, etc. into emergency spillways because presumably they will rarely if ever be used.”

“We did not say it was a cost issue,” he added.

Brown, after meeting with advisors at the state’s emergency operations center near Sacramento, was asked by reporters about the concerns raised in 2005 about Oroville’s spillway system.

He said he welcomed calls for more scrutiny. “We’re in a very complex society where things can go wrong,” he said. “When they do, they ripple out and affect hundreds of thousands and in some cases millions of people.”

Times staff writers John Myers in Sacramento and Veronica Rocha, Joseph Serna and Rong-Gong Lin II in Los Angeles contributed to this report.

chris.megerian@latimes.com | Twitter: @chrismegerian

bettina.boxall@latimes.com | Twitter: @boxall

melanie.mason@latimes.com | Twitter: @melmason

laura.nelson@latimes.com | Twitter: @laura_nelson

ALSO

Engineers race to lower water level of Oroville reservoir before new storms move in

The frantic fight to keep the Oroville Dam crisis from turning into a catastrophe

Diagram explains the problem with Oroville Dam’s emergency spillway

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