200,000 Californians face delay in return to homes at risk from damaged dam
The water level has dropped behind the US's tallest dam, reducing the risk of a catastrophic spillway collapse, but nearly 200,000 people ordered to leave their homes may have to stay away until a damaged barrier is repaired.
The California Department of Water Resources is considering using helicopters to drop loads of rock on the eroded spillway at Lake Oroville, about 150 miles north east of San Francisco, but police could give no timetable for the work.
With more rainstorms expected later in the week, time is running short to fix the damage.
Authorities ordered mass evacuations on Sunday for everyone living below the lake out of concern that the spillway could fail and send a 30ft wall of water downstream.
The acting head of California's water agency said he is "not sure anything went wrong" on the damaged spillway.
Bill Croyle's comments came after officials had assured residents for days that the damage was nothing to be concerned about - then ordered everyone to get out in an hour.
The water level in the lake had risen significantly in recent weeks after storms dumped rain and snow across California, particularly in northern parts of the state.
The high water forced the use of the dam's emergency overflow for the first time in the dam's near 50-year history on Saturday.
The threat appeared to ease on Monday as the water level fell. Officials said water was flowing out of the lake at nearly twice the rate as water flowing into it.
Sunday afternoon's evacuation order came after engineers spotted a hole in the earthen secondary spillway for the 770ft tall Oroville Dam and told authorities it could fail within the hour.
With more rain expected on Wednesday and Thursday, officials are rushing to try to fix the damage and hoping to reduce the dam's water level by 50ft ahead of the storms.
The sudden evacuation panicked residents, who scrambled to get their belongings into cars and then grew angry as they sat in bumper-to-bumper traffic hours after the order was given.
A Red Cross spokeswoman said more than 500 people showed up at an evacuation centre in Chico, California.
The shelter ran out of blankets and bed, and a lorry with 1,000 more cots was stuck in the traffic fleeing the potential flooding on Sunday night, Red Cross shelter manager Pam Deditch said.
A California Highway Patrol spokesman said two planes would fly to help with traffic control and possible search-and-rescue missions.
At least 250 California police officers were posted near the dam and along evacuation routes to manage the exodus and ensure evacuated towns do not become targets for looting or other criminal activity.
About 188,000 residents of Yuba, Sutter and Butte counties were ordered to evacuate.
The erosion at the head of the emergency spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville.
Those flows could overwhelm the Feather River and other downstream waterways and levees and flood towns in the three counties.
Department engineer and spokesman Kevin Dossey told the Sacramento Bee the emergency spillway was rated to handle 250,000 cubic feet per second, but it began to show weakness on Sunday after flows peaked at 12,600 cubic feet per second.
The California National Guard notified all its 23,000 soldiers and airmen to be ready to deploy, the first time an alert for the entire state National Guard had been issued since the 1992 riots in Los Angeles.
The lake is a central piece of California's government-run water delivery network, supplying the state's Central Valley agricultural heartland and homes and businesses in southern California.