OROVILLE — The threat of imminent collapse of the Oroville Dam emergency spillway eased Sunday night, hours after authorities ordered the evacuation of more than 100,000 downstream residents upon discovering damage to the structure.

But there is still serious concern about the condition of the auxiliary spillway, and it’s unclear when residents will be able to return to their homes.

With a storm expected to arrive Wednesday, the state Department of Water Resources needs to make room for the water that will be flowing in. The agency aims to drain about 1.2 million acre feet of water from the reservoir over the next day or so. The capacity of the reservoir, California’s second-largest, is about 35 million feet.

Gov. Jerry Brown declared an emergency late Sunday to beef up the state’s response to the evacuations and dam threat.

The evacuation of residents in Oroville and surrounding communities in the shadow of the nation’s tallest dam was issued around 4:30 p.m., with California Department of Water Resources officials saying floodwaters could arrive within the hour. By 8 p.m., the crisis had eased, as the water level of Lake Oroville, the state’s second-largest reservoir, had fallen to the point — roughly 900 feet — that no water was passing over the imperiled auxiliary spillway.

Law enforcement officials expressed sympathy for residents forced to flee the potential disaster. The sheriff of Butte County said it was better to be “safe than sorry” given the gravity of the situation.

“I didn’t have the luxury seeing if everything was going to be OK,” Sheriff Kory Honea late Sunday afternoon. “We needed to get people moving quickly in order to save lives in case the worst-case scenario came to fruition.”

The evacuation caused chaos on roads and highways as people hustled out of their homes with scant belongings.

Some Marysville evacuees were bordering on panic. Erin English, of Linda, fled with her husband, two children and dogs.
“I’m scared to death. I’ve never been through anything like this before,” she said. “I pray for the safety of everybody here.”

Evacuees were quickly filling up hotels along Highway 99 and Interstate 5 in Sacramento. In an hour Sunday evening, the Homewood Suites near Sacramento International Airport received 20 reservations in back-to-back phone calls, said Gao Hang, who was working the front desk.

“They didn’t care about the price at all because they just need a place to go,” she said. “It’s not just us.”

Just four hours before the evacuation, water officials held a news conference during which they said the emergency spillway, activated Saturday for the first time in its history because of damage the main spillway sustained early last week, was not in danger of failing. However, officials soon discovered that a hole was developing — one that was growing fast enough to cause a breach.

Officials ramped the main spillway back up Sunday afternoon — from 55,000 cubic feet of water per second to 100,000 — to lower the level of the reservoir and ease the risk of a catastrophic failure of the emergency spillway.

Authorities breathed a sigh of relief as the main spillway held up under the pressure and the erosion of the earthen hill beneath the emergency spillway did not worsen as rapidly as feared.

“It’s definitely one of those white-knuckle moments,” said Jay Lund, an engineering professor at UC Davis.

The sheriff said there is a plan to plug the hole in the emergency spillway.

“That would include using helicopters to drop bags of rocks into the crevice to prevent any further erosion,” he said.

Water expert Peter Gleick, of the Pacific Institute, said failure of the emergency spillway would allow an uncontrolled release of water to surge down the Feather River. Such a breach could then undermine the earthen hill beneath the spillway, causing a catastrophic release from the reservoir.

He cautioned Sunday night the catastrophic scenario did not appear likely, but engineers will know more when they inspect the damage to the emergency spillway in coming days.

“People don’t realize how powerful water can be,” Gleick said. “We use water to cut steel in some industrial operations. Uncontrolled water is a dangerous thing.”

Water district officials have repeatedly said that the dam itself is structurally sound and not at risk of failing.

The evacuation orders affected 35,000 people in Butte County, 65,000 people in Yuba City, and 75,000 people in Yuba County, authorities said.

Some residents obeyed the orders reluctantly. Kevin Carroll lives in a Marysville home along the Feather River, and gathered clothes and his dogs to head out, even though he believed the river would not flood.

“My wife said go,” he said. “The river is right on our back door.”

Except for the crowded roads Sunday, Oroville looked liked a ghost town.

Evacuation centers were filling up Sunday night in communities surrounding the evacuated region.

Butte County Superintendent of Schools Tim Taylor has called for nearly all schools to close Monday except those in the Chico and Paradise districts.

The city of Oroville has about 16,000 residents. Karl Swanberg, a forecaster with the National Weather Service, said a failure of the spillway could potentially affect most of the town.

“This is not a drill,” a National Weather Service bulletin blared Sunday afternoon. “Repeat this is not a drill … Move to higher ground now. Act quickly to protect your life.”

Lake Oroville opened in 1968. Oroville Dam, located 70 miles north of Sacramento in the Sierra Nevada foothills, is a critical part of California’s drinking water system, providing water for 23 million people and vast stretches of farmland.

At 770 feet tall, the structure that holds back the Feather River is taller than the Washington Monument.