OROVILLE, California--Stormwaters subsided on Monday behind the nation's tallest dam, in Northern California, as engineers raced to drain the rain-swollen reservoir and shore up a crumbling overflow channel before new storms sweep the region later this week.
Authorities said they averted the immediate danger of a catastrophic failure - one capable of unleashing a wall of water three stories tall on towns below.
A mandatory evacuation of about 188,000 residents remains in effect, Butte County Sheriff Kory Honea said at a midday news conference. The potential danger for the Feather River valley below the Lake Oroville Dam, 65 miles (105 km) north of Sacramento, was still being reviewed, he said.
"We need to have time to make sure that before we allow people back into those areas it is safe to do so," he said.
Residents below the dam were abruptly ordered from their homes on Sunday when an emergency spillway that acts as an automatic overflow channel appeared in danger of imminent collapse from severe erosion. Alfred Ybarra had gone down to the Feather River with his children on Sunday to watch the swollen waters.
"Within minutes the water was up to the tires on my car," Ybarra said. "I told my kids, 'You have to pray. It's the only thing that you can do."
Asked whether he thought officials had overreacted by ordering evacuations, Ybarra said, "Absolutely not."
The main spillway, a separate channel, is also damaged because part of its concrete lining fell apart last week. Both spillways are to the side of the dam, which has not been compromised, engineers said.
The situation grew less dire several hours later on Sunday as water levels subsided behind the dam, leaving the weakened unpaved emergency spillway largely intact. By Monday, the level of the lake had dropped enough so that water was no longer pouring over the hill.
Erosion caused by the hole in the side of the main spillway appeared to have abated by Monday, and it was back to more or less normal operations, officials said. The aim is to lower the reservoir's overall water level by 50 feet - and prevent further spillover down the emergency hillside channel - before more rain arrives in the coming weeks and before snow-melt runoff begins in the spring, acting state water resources director Bill Croyle told reporters on Monday. He said he hoped to achieve that goal in the next 10 to 15 days.
