CHICO, Calif — Though the level of California's second largest reservoir dropped about 3.5 feet overnight, communities downstream still face the threat of extreme flooding, officials said Monday.
A pair of storms are expected to hit the state this week, and forecasters say they will be strong enough to bring 2 to 6 inches of rain to Oroville, where the concrete spillway at Oroville Dam has been crumbling since Tuesday and an emergency earthen spillway with a concrete lip was eroding so severely Sunday that officials warned a 30-foot wall of water could be unleashed on Oroville and other towns along the Feather River.
At least 188,000 residents were ordered to evacuate the area, about 150 miles northeast of San Francisco, late Sunday.
Forecasters anticipate a moderate storm Wednesday with a “really big and strong” storm Friday, said Brandt Maxwell, National Weather Service meteorologist. Another 8 inches of rain could fall in the mountains before draining into Lake Oroville, and that would increase the flow of water at the dam where severe erosion could drop the top of the spillway enough for water to pour out uncontrolled.
“If they haven’t found something really good to do by Friday, things are going to go downhill further,” Maxwell said. “That could be a really strong storm, not just lots of rain but lots of wind, too.”
State water officials continue to reduce the lake's water level by 50 feet in anticipation of the storms. That would allow more room for runoff and allow water officials to stop using the spillways entirely so they can make repairs to the crumbling main spillway.
The storms — particularly the one Friday — have been on forecasters’ radar for several days and could be large enough to cause flash flooding anywhere in the Golden State. The storms will hit Northern California before making their way south, Maxwell said.
State water experts don't know why the emergency spillway eroded after water was sent down it Sunday for the first time in the dam's almost 50-year history, said California's acting director of water resources, Bill Croyle.
“I’m not sure anything went wrong,” he said. “That system has been installed since the early 1960s. It’s been monitored, but I’m not sure what caused the damage itself. It’s designed for higher flows."
Photos: Thousands evacuated near Oroville Dam in Calif.
On Sunday, the mandatory evacuation order below Oroville Dam triggered a chaotic exodus, filling highways as evacuees headed north and west toward higher ground. An emergency shelter at the Silver Dollar Fairgrounds here, 24 miles north, filled within hours. Several other shelters were established.
The emergency spillway had never been activated since the dam was topped off in October 1967 but was pressed into service because Oroville Dam's main concrete spillway developed a 200-foot long, 30-foot deep hole Tuesday that continues to erode. Both spillways sit off to the side of the dam itself.
Officials said the main structure remains sound.
In an effort to preserve the concrete lip of the emergency spillway, operators with the California Department of Water Resources doubled flows Sunday into the main spillway despite its bottom being largely washed out.
With 100,000 cubic feet of water leaving Lake Oroville each second, the lake level dropped quickly. That relieved some pressure on the emergency chute, but it also chewed more concrete from the bed of the main spillway.
The most recent inspection of the Oroville Dam’s main spillway didn’t include a close examination of the structure, according to a California safety report released in July.
“A visual inspection from some distance indicated no visible signs of concrete deficiencies,” according to the report from the California Division of Safety of Dams. It was unclear why the spillway was not more closely inspected, Chris Orrock, a Division of Dam Safety spokesman, said last week.
Officials were hopeful that increased use of the main spillway would save the emergency backup chute, and that efforts to back fill the auxiliary spillway's holes with bags of rocks could shore it up Monday. California's National Guard said it would provide eight helicopters to assist with reconstruction efforts.
In light of the possibility of the auxiliary spillway’s imminent collapse, Butte County Sheriff Kory Honea said Sunday that he had no choice but to order an evacuation.
“I didn’t have the luxury of waiting to see if all was OK. We need to get people moving quickly and to save lives in case the worst case came to fruition,” Honea said. “This is a very dynamic situation. This is a situation that could change very, very rapidly,” he said.
It remained unclear when residents might be allowed to return home. Croyle of the state water resources department said his agency may need 15 days or longer to put a plan in place to make repairs.
“The danger could persist for a day or two or even longer,” said Kelly Houston, deputy director of the California Governor’s Office of Emergency Services State Operations Center. “People should not have an expectation they would come back (home) in a short number of hours. ... We don’t know what Mother Nature is going to do.”
It also wasn’t clear how many had defied the order or been unable to leave.
Lucy Watt, 65, of Oroville decided to spend Sunday night in her car on top of the dam, figuring it was the safest place to be.
"Everybody's scared." But she said Monday that she was more cold than scared; temperatures were in the upper 40s overnight.
Those who defied the continuing mandatory evacuation order and came home early returned to ghost towns — closed shops, empty parking lots and nervous calm in neighborhoods. Most of the activity was happening at gas stations and convenience stores that stayed open.
“My faith supercedes everything else and I just feel like I’ll be safe," said James Campbell, 47, of Oroville. "We will be fine.”
Janet Frye, 48, found her Yuba City, Calif., home, two miles from the Feather River, just as she had left it with special photo albums on the highest shelves. She returned to check on friends and planned to stay with other friends in Colusa County.
But George Ayers, who's 82 and uses a wheelchair, said he'll stay put in Oroville.
"I'm crippled up real bad. But you know, it's silly," Ayers said of the evacuation order. "I've been in this town over 50 years, and I don't let too much scare me."
• On Tuesday, state Department of Water Resources officials identified the hole in the dam's spillway.
• On Thursday, they said they knew of “no imminent or expected threat to public safety or the integrity of Oroville Dam.”
• On Friday, reservoir operators were saying if the current releases from the nearly full reservoir could be maintained, it was less likely the lake would rise to the point where the emergency spillway would be needed. But if it was needed, that probably would happen Saturday, adding that it was within the agency’s contingency plans and posed no flood threat downstream.
Sunday was when officials discovered the problem with the emergency spillway, where water from Lake Oroville for the first time in the dam's nearly 50-year history began flowing Saturday.
The lake came within a foot of spilling into it in January 1997, officials said.
Contributing: Colin Atagi, The (Palm Springs, Calif.) Desert Sun; Reno (Nev.) Gazette-Journal