Nearly 200,000 people living downstream from the tallest dam in the US were ordered to evacuate their homes on Sunday because an overflow channel appeared to be in danger of imminent collapse.
The abrupt evacuation order was issued mid-afternoon, as authorities determined that the auxiliary spillway on the Lake Oroville dam in northern California could give way, potentially unleashing a wall of water on to rural communities along the Feather river.
“Immediate evacuation from the low levels of Oroville and areas downstream is ordered,” the Butte County sheriff said in a statement on Facebook. “This is not a drill.”
The California department of water resources said the overflow channel was “predicted to fail within the next hour”.
Several hours later the threat had receded and the overflow channel remained intact, though the evacuation order was still in place.
The water resources department said helicopters would drop rocks to fill a gap in the channel. Authorities were also releasing water to lower the lake’s level.
By 10pm, state and local officials said those efforts had paid off and, with water no longer flowing over the eroded channel, the immediate danger had passed. But they cautioned that the situation remained unpredictable.
“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.
The dam, whose structure remains sound, is nearly full following a wave of winter storms that brought relief to the state after four years of devastating drought. Water levels were less than 7ft (2 metres) from the top of the dam on Friday.
NWS Sacramento (@NWSSacramento)6:08pm: #OrovilleDam itself is not compromised at current time. Failure would be on auxiliary spillway. See graphic for details. pic.twitter.com/LSxCwsthxC
February 13, 2017
The Butte County sheriff, Kory 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.
Evacuation orders remained in place for 188,000 people in Oroville, Yuba County, Butte County, Marysville and nearby communities. The Yuba County office of emergency services urged evacuees to travel only to the east, south or west. “Do not travel north toward Oroville,” the department said on Twitter.
Evacuation centres were set up in Chico, California, about 20 miles (32km) north-west of Oroville, but major highways leading south out of the area were jammed as residents fled the flood zone.
David Little (@ER_DavidLittle)
It's gridlock in Yuba City where highways 20 and 99 come together. Photo from @selljo_ , who's stuck in it. pic.twitter.com/IFe7teA1Ni
February 13, 2017
Caltrans District 3 (@CaltransDist3)
Traffic backed up getting out of Marysville due to evacuation notice for Oroville Adam. pic.twitter.com/3tlSCmlwky
February 13, 2017
The California 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.
Gov. Brown Press Ofc (@GovPressOffice)
.@JerryBrownGov Issues Emergency Order to Help Response to #OrovilleSpillway https://t.co/RW8XBlLFT6 pic.twitter.com/ULQGjkt1c1
February 13, 2017
Brown asked the Federal Emergency Management Agency on Friday to declare the area a major disaster due to flooding and mudslides brought on by recent storms.
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 metres high, the structure, built between 1962 and 1968, is the tallest dam in the US, topping the famed Hoover dam by more than 12 metres.
This is the first time in the dam’s history that water has flowed above the overflow channel. The structure is expected to face further strain in the coming months as northern California faces its wettest ever winter.
Reuters contributed to this report
- This article was amended on 13 February 2017. The headline of a previous version incorrectly stated that the evacuation was due to the potential collapse of the dam; it was the dam’s spillway, and the threat to residents was from flooding.
