Crumbling California dam spillway prompts urgent evacuations

Residents below the tallest dam in the United States, near Oroville in Northern California, were urgently ordered to evacuate on Sunday after a spillway appeared for a time to be in danger of imminent collapse.

The abrupt evacuation of at least 130,000 people came as authorities said that a crumbling auxiliary spillway on the Lake Oroville Dam could give way, unleashing floodwaters onto 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 posted on social media. "This is NOT A Drill."

The California Department of Water Resources said on Twitter at about 4:30 p.m. PST (0030 GMT Monday) that the spillway next to the dam was "predicted to fail within the next hour."

While it was still standing nearly three hours later, the Water Resources department said crews would use helicopters to drop rocks to fill a gouge in the spillway.

Authorities were also releasing water to lower the lake's level.

Officials said the cities of Oroville, Gridley, Live Oak, Marysville, Wheat land, Yuba City, Plumas Lake, and Olivehurst were all under evacuation orders.

Several hours later the situation appeared less dire as the spillway remained standing some five hours.

Butte County Sheriff Korey Honea said at an evening press conference that he was told by experts earlier on Sunday that the hole that was being created in the spillway could compromise the structure. Rather than risk thousands of lives, the sheriff said, a decision was made to order the evacuations.

But he said he was told later that the erosion was not progressing as rapidly as earlier feared and that the amount of water flowing over the spillway had dropped quickly.

Still, evacuation orders remained in place. 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 at a fairgrounds in Chico, California, about 20 miles northwest of Oroville, but major highways leading south out of the area were jammed as residents fled the flood zone.

Oroville itself was largely deserted after nightfall.