OROVILLE, Calif. _ Tens of thousands of residents in Northern California were ordered to immediately evacuate Sunday afternoon after erosion at the emergency spillway on the Oroville Dam threatened to flood Oroville and nearby towns below.
Officials said late Sunday that they will use bags of rocks to try to plug the hole at the head of the emergency spillway, and also will reduce the water level at Lake Oroville to alleviate stress on the spillway.
They emphasized the situation remains dangerous at the nation's tallest dam and urged residents in communities along the Feather River to evacuate to higher ground.
The National Weather Service initially said the auxiliary spillway at the Oroville Dam was expected to fail at about 5:45 p.m. PST, which could send an "uncontrolled release of flood waters from Lake Oroville."
Butte County Sheriff Kory L. Honea said that a crevice was developing near the lower edge of the emergency spillway and eroding "at a rather significant rate."
"There was significant concern that (the hole) would compromise the integrity of the spillway, resulting in a substantial release of water," Honea said. "We had to make a very critical and difficult decision to initiate the evacuation of the Oroville area."
Those in Oroville, a city of about 16,000 people, were asked to flee northward toward Chico, along with Gridley and Biggs. In Yuba County, those in Marysville and other communities in the county's valley floor were urged to take routes to the east, south or west. In Sutter County, evacuations were ordered for Yuba City, Live Oak, Nicolaus and all communities around the Feather River basin.
"This is not a drill. This is not a drill. Repeat, this is not a drill," the National Weather Service said. Authorities urged residents to contact neighbors and family members and reach out to the elderly and assist them in evacuating.
By Sunday night, state officials determined the erosion rate for the hole at the emergency spillway had slowed, and experts were devising a plan to dump bags of rocks into the crevice to plug the hole, Honea said.
To slow the erosion on the emergency spillway, state Department of Water Resources officials also doubled the flow of water down the main spillway to 100,000 cubic feet per second. The rapid increase drastically reduced the water coming over the emergency spillway to two inches, Honea said.
The dam itself is structurally sound, officials said.
The evacuations marked a dramatic turn of events at the Oroville Dam, located about 75 miles north of Sacramento.
For several days, officials have been trying to figure out how to get water out of Lake Oroville after the main spillway was damaged. A massive hole was discovered last week on the main spillway and eventually spread across the full width of the concrete-lined channel.
Saturday marked the first time the emergency spillway was used since the dam was finished in 1968, and until Sunday afternoon it seemed to be working well. But water from rain and snow continued to flow into Lake Oroville at a rapid pace, causing water levels to rise to emergency levels.
Lake Oroville is the linchpin of California's state water movement system, sending water from the Sierra Nevada south to the farms across the San Joaquin Valley and cities in Southern California.
Video from television helicopters Sunday evening showed water flowing into a parking lot next to the dam, with large flows going down both the damaged main spillway and the emergency spillway.
Officials feared a failure of the emergency spillway could cause huge amounts of water to flow into the Feather River, which runs through downtown Oroville, and other waterways. The result could be flooding and levee failures for miles south of the dam, depending on how much water is released.
The videos also showed lines of cars getting out of downtown Oroville. An evacuation center was set up at the Silver Dollar Fairgrounds in Chico.
Sergia Richard-Madrid, 62, was working her shift at Home Depot on Sunday afternoon when phones began to ring about the mandatory evacuation.
She rushed home but the rest of her family had already left. Some fled north to Chico, but she headed south on Highway 70 and was diverted when authorities began evacuating low-lying Marysville as well, about an hour south of Oroville.
Near downtown Oroville four people were standing on a bridge overlooking the river.
James Nash, 86, heard about the evacuation order from his apartment building manager. A retired chef and Korean War vet, he wasn't sure where to go, and was upset that Oroville didn't seem to be doing more.
He couldn't get to Chico on his bike. He had a small bag with shaving gear, washcloth and paper towels. "No blankets. No water."
He remembered the 1997 evacuation order, which he ignored and which did not result in flooding. He said he's still pretty sure nothing will happen this time: "I don't believe it's going to happen."
But he wasn't comfortable enough to return home, so he kept watching the water in the river below. "I'm getting bored," he said.
Diminished by years of drought conditions, Lake Oroville had become a symbol of the state's worsening water crisis. But an unusually wet winter took the lake from nearly full to overflowing in less than a week.
At the same time, the nearly mile-long main spillway that the dam's managers rely on to release excess water began to crumble, with erosion worsening as millions of gallons of water poured over it.
Realizing the lake might rise to a level that would trigger the use of an emergency spillway, state workers began clearing the area of trees and brush that could be sent hurtling downstream.
On Saturday morning, water began washing over the dam's emergency spillway for the first time since it was completed in 1968. Photographs showed a torrent of water rushing downhill to join the Feather River.
On Sunday, officials said that although they expected the uncontrolled spill to end, they plan to continue using the concrete spillway to create more storage in the reservoir in anticipation of rainfall later in the week.
"We're going to continue to flow water down the spillway and lower the lake," See said. "You're going to see the lake dropping over the next several days."
Officials emphasized that despite the damage to the spillways, the dam itself was not at risk of failing.
"Believe me, in the last several days there have been a lot of eyes on it," said Bill Croyle, acting director of the water department. "Oroville Dam is not in any way a part of the damage that occurred."
Officials have estimated it could cost $100 million to $200 million to repair the damage to the spillway and other features.
