Emergency workers and state officials were racing on Monday to repair a damaged spillway on the tallest dam in the United States, while almost 200,000 people evacuated downstream of the structure were given no indication of when they might return to their homes.

Lake Oroville dam: mass evacuation ordered over flooding threat Read more

While the imminent threat of a breach in the spillway wall appeared to have receded overnight, the forecast is for a week of continuous rain around Lake Oroville, in northern California, starting on Wednesday.

Helicopters from around the state were sent to the site of the Oroville dam – the tallest in the United States – to assist in the emergency effort, according to local news reports. Crews loaded bags of rocks on to helicopters, which were to be flown over the damaged spillway to fill the gap created by erosion.



The emergency repair work comes one day after tens of thousands of people living close to the dam were ordered to evacuate on Sunday afternoon when the spillway appeared to be in danger of collapse.

Evacuee centers have been established at county fairgrounds and community centers. Local Sikh temples have also opened their doors. The state has not provided any timeline as to when the evacuation orders will be lifted.



“I recognize what a hardship this has placed on our community,” the Butte County sheriff, Kory Honea, said at a midday press conference. The evacuation order “was a hard decision to make”, he added, and will be “equally difficult” to lift.

Bill Croyle of the department of water resources said that the focus was now on releasing water from the reservoir in order to create more storage room.

“We’re working to … move as much water out of the reservoir so we have space for the storms that are coming in,” Croyle said, adding that the storm forecast for this week will probably be smaller than the storm that precipitated the current crisis.

Facebook Twitter Pinterest The California department of water resources has suspended flows from the Oroville dam spillway after a concrete section eroded. Photograph: Handout/Getty Images

At the evacuation center in Chico, a small town just north of Oroville, scores of families parked cars, pickup trucks and RVs in a gravel lot, awaiting information. Vehicles were filled with hastily filled bags and laundry bins filled with clothes and snacks.



Curtis Young, in his 80s, sat with his family and their two dogs in a small, battered SUV, stewing over how officials had handled the chaotic evacuation the night before from Gridley. “I’m old enough not to care. I’ll tell them to their faces that you’re either a liar, an idiot or both,” he said.

All week he was aware officials had told residents not to worry about the dam, he said, until around 5.30pm on Sunday, when a friend called to say there was an evacuation order. Young said he left with barely more than “a pack of smokes and a hundred dollars”.

His friend, who gave his name as Gabe, said that there was no detail in the order except to move. “Just get your dogs in the car and go,” he said.

The state water resources board announced on Sunday: “This is not a drill.” It warned that the failure of the spillway would “result in an uncontrolled release of flood waters from Lake Oroville”.

Lake Oroville, the state’s second-largest reservoir, has been filled to the brim thanks to an unusually wet winter that has brought an end to the region’s years of severe drought. Last week, for the first time in the dam’s history, water flowed over the top of the spillway.



According to the San Jose Mercury News, the spillway was designed to handle 350,000 cubic feet per second of water. But on Sunday, flows were just a fraction of that – up to 12,000 cubic feet per second – when officials observed enough erosion to make them fear the entire spillway was in danger of imminent collapse.

“Once you have damage to a structure like that, it’s catastrophic,” Bill Croyle, acting director of the water resources department, told a press conference.

Sheriff Honea said he was told by experts earlier on Sunday that the hole being created in the channel could compromise the structure. Rather than risk thousands of lives, Honea said, a decision was made to order the evacuations.

Major highways in the area were quickly jammed as residents raced to escape the flood zone. Overnight, however, the danger receded. State officials are releasing water to lower the level of the lake, and water is no longer flowing over the spillway.

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California’s governor, Jerry Brown, issued an emergency order that he said would bolster the state’s response. “I’ve been in close contact with emergency personnel managing the situation in Oroville throughout the weekend and it’s clear the circumstances are complex and rapidly changing,” he said.

The dam is about 70 miles north of Sacramento, and just upstream and to the east of Oroville, a city of more than 16,260 people. At 230 meters high, the structure, built between 1962 and 1968, is the tallest dam in the US, topping the famed Hoover dam by more than 12 meters.

The weakness of the emergency spillway was foreseen 12 years ago by three environmental groups, according to the San Jose Mercury News. The Friends of the River, the Sierra Club and the South Yuba Citizens League filed a motion in October 2005 asking the government to require that the emergency spillway be reinforced with concrete.

The groups warned that the earthen spillway was vulnerable to erosion and could cause massive flooding or even fail. The government rejected their appeal, insisting that the spillway was safe.

Croyle refused to answer questions about the issue at the press conference on Monday, saying that they were focused on the immediate situation.