Evacuation order remains amid dam erosion concerns
OROVILLE, California — Nearly 200,000 people who were ordered to leave their homes after a California spillway threatened to unleash a ninemetre wall of water may not be able to return until significant erosion is repaired, authorities said Monday.
The officials who issued the hasty evacuation order defended their decision, saying it was necessary to ensure public safety in the region downstream from the U.S.’s tallest dam at 235 metres, about 240 kilometres northeast of San Francisco. Engineers spotted a hole in the spillway, which they feared could have failed within an hour.
The water level of the massive reservoir known as Lake Oroville dropped Monday, slightly easing fears of a catastrophic collapse. But with more storms on the horizon, crews raced to assess what happened and began dumping large boulders and sandbags into the spillway to prevent any more erosion.
The acting head of the state’s Department of Water Resources said he did not know if anything had gone wrong and was unaware of a 2005 report that recommended fortifying the earthen emergency spillway with concrete for just such an event. The spillway had never been used in the dam’s 50 years of operation, and it was not near capacity when it began to fail.
“I’m not sure anything went wrong,” Bill Croyle said. “This was a new, never-having-happened-before event.”
Croyle and the local sheriff sought to reassure the public that downstream communities were safe until water began spilling over the lake’s edge Sunday and a chocolate-colored torrent of water began chewing through the slope below it.
The state’s Department of Water Resources had said conditions were stable at noon and then tweeted an evacuation warning at 4:45 p.m. of a possible failure within the hour, saying “this is not a drill.”
Chaos ensued as anxious residents rushed to pack up their families and abandon several communities in Butte, Yuba and Sutter Counties.
The area in the northern Central Valley is known mainly for agriculture, which is fed by dammed-up rivers that spill down from the Sierra Nevada foothills nearby.
It took some people seven hours to travel to evacuation centres that should have been an hour away.
The Department of Water Resources began releasing water down its main spillway last week to make more room in the reservoir behind dam.
After a chunk of concrete tore out of the spillway, creating a 60metre-long, nine-metredeep hole that continues growing, water managers began using the emergency spillway for the first time in its 48-year history.