California dam evacuees can return home, but need to be ready to leave again

Authorities lifted an evacuation order Tuesday allowing 200,000 California residents who live below the nation's tallest dam to return home after declaring the risk of a catastrophic collapse of a damaged spillway had been significantly reduced.

Butte County SheriffKoryHoneasaid residents can return home immediately. State water officials said they have drained enough of the lake behindOrovilleDam so that its earthen emergency spillway will not be needed to handle runoff from an approaching storm.

• What to know about California's failingOrovilleDam

Residents returning home "have to be vigilant," and "there is the prospect that we will issue another evacuation order ... if the situation changes," the sheriff said.

Officials had ordered residentsof the region, 242 kilometres northeast of San Francisco,to flee to higher ground Sunday after fearing a never-before-used emergency spillway was close to failing and sending a 10-metre wall of water into communities downstream.

Rod Remocal of Biggs, west of Oroville, said the announcement "took a big load off" of him. He called it "the thrill of relief."

The decision to lift the order came abruptly, just as the evacuation order Sunday night came shortly after officials said there was no threat.

The sheriff said water was being released through the dam's damaged primary spillway without further harm to the concrete structure. Work to cover the earthen emergency spillway with rocks and cement was on pace to beat the next rain, and those storms would be less potent.

Risks reduced

"As a result of these actions, the risks that we faced when we initiated those evacuations have significantly been reduced," Honea said.

"This reduction to an evacuation warning properly balances the need for people to resume their daily lives while at the same time being prepared to deal with future increased threat," he added.

The decision came as helicopters carried giant sandbags and cement blocks from a staging area on the south side of Oroville Dam toward the stricken spillway on the north side. Crews operating heavy equipment loaded rocks and boulders into dump trucks, which carried them over the dam and dumped them on damaged portions.

Bill Croyle, acting director of the state Department of Water Resources, said that as of noon Tuesday, water was flowing into the lake at a rate far lower than the water being released.

"That means we're continuing to make significant gains," Croyle said.

The surface of the reservoir was nearly four metres lower than at its peak height, and the water release, described as the greatest in the dam's nearly half century, will continue to lower the surface a total of 15 metres.

The National Weather Service's Sacramento office said the incoming rain would move through late Wednesday and Thursday morning, with five centimetres to 10 centimetres expected in the foothills and mountains. But the storm was looking colder than initially projected, meaning less snow and less run-off than last week's storms.

White House spokesman SeanSpicertold reporters Tuesday the administration would "make sure we are doing everything wecan to attend to this matter" and "help people who have beenimpacted," adding that the dam was evidence that the UnitedStates needed to overhaul its infrastructure, one of Trump'sdomestic goals.

On Tuesday evening, the government announced that three counties in the areawill receivefederal disaster assistance.

The earth-filled dam is just upstream and east ofOroville,a town of about 16,000 people. At 230 metreshigh,the structure, built between 1962 and 1968, is some 12 metres taller than the Hoover Dam.

On Monday afternoon, crews dropped large bags filled withrocks into a gap at the top of the emergency spillway to rebuildthe eroded hillside.

The main spillway, a separate channel, is also damagedbecause part of its concrete lining fell apart last week. Bothspillways are to the side of the dam itself, which has not beencompromised, engineers said.