Tens of thousands of residents in Northern California were ordered to immediately evacuate Sunday afternoon after erosion at the emergency spillway at Lake Oroville threatened to flood downstream towns.
The flood danger emerged suddenly when a hole developed Sunday in the auxiliary spillway that was being used to lower the levels of the full-to-the brim reservoir, the second-largest in California.
The erosion could undermine the concrete top of the spillway, allowing torrents of water to wash downhill into the Feather River and flood Oroville and other towns in Yuba, Sutter and Butte counties.
Sunday night, officials said the threat had diminished because the lake level had dropped and water was no longer washing over the emergency spillway.
But the situation at Oroville remained precarious. The two main avenues for getting water out of the lake – the unpaved emergency spillway and the main concrete spillway – were both damaged.
Both spillways are separate from Oroville Dam itself, which state officials continued to say was not in danger. The main spillway, a long concrete chute off to the side of the dam, has a gaping gash in it that forced officials to reduce releases last week.
But a new storm system forecast for later this week put water officials on a race against time. Bill Croyle, the acting director of the state Department of Water Resources, said they planned to continue discharging flows at a rate of 100,000 cubic feet per second, with the hope of lowering the reservoir level by 50 feet.
Officials also said they would use bags of rocks to try to plug the hole at the emergency spillway. They emphasized the situation remains dangerous at the reservoir and urged residents in communities along the Feather River to evacuate to higher ground.
Those in Oroville, a city of about 16,000 people, were asked to flee northward toward Chico, along with Gridley and Biggs. In Yuba County, those in Marysville and other communities in the county’s valley floor were urged to take routes to the east, south or west. In Sutter County, evacuations were ordered for Yuba City, Live Oak, Nicolaus and all communities around the Feather River basin.This is not a drill. This is not a drill. Repeat, this is not a drill
“This is not a drill. This is not a drill. Repeat, this is not a drill,” proclaimed a Sheriff’s Department statement posted on social media. Authorities urged residents to contact neighbors and family members and reach out to the elderly and assist them in evacuating.
About 188,000 residents near Oroville, Calif. were ordered to evacuate Sunday after a hole in an emergency spillway in the Oroville Dam threatened to flood the surrounding area. Thousands clogged highways leading out of the area headed south, north and west and arteries major and minor remained jammed as midnight approached on the West Coast.
Lake Oroville is one of California’s largest man-made lakes with 3.5 million acre-feet of water and 167 miles of shoreline, and the 770-foot-tall Oroville Dam is the nation’s tallest, about 44 feet higher than Hoover Dam on the Colorado River. The lake is the linchpin of California’s government-run water delivery system, sending water from the Sierra Nevada for agriculture in the Central Valley and for residents and businesses in Southern California.
Earlier this week, unexpected erosion crumbled through the main spillway, sending chunks of concrete flying and creating a large hole. Then sheets of water began spilling over the dam’s emergency spillway for the first time in its nearly 50-year history.
Water from rain and snow rapidly flowed into the lake, causing it to rise to perilous levels, and sending water down the wooded hillside’s emergency spillway, carrying murky debris into the Feather River below.“Once we have damage to a structure like that, it’s catastrophic,”
Bill Croyle, acting director of the state’s Department of Water Resources, said in a 10 p.m. news conference Sunday, in reference to the erosion of the main spillway. “We determined we could not fix the hole. You don’t just throw a little bit of rock in it.”
dohboi wrote:They seem to have now gotten the water level down below the level that it would further erode the emergency spillway gash, and it isn't supposed to rain for a couple days, so it would seem that the worst is over. But who knows? It doesn't sound as if they are calling back the nearly two hundred thousand evacuees yet. One official described the situation as 'dynamic' and 'could change anytime.'
As mentioned above, it's going to take hundreds of millions of dollars and many years to fix these problems, and in the mean time, water will not be as available as it should be if everything was functioning properly.
http://abcnews.go.com/US/thousands-evac ... d=45450195
More than a decade ago, federal and state officials and some of California’s largest water agencies rejected concerns that the massive earthen spillway at Oroville Dam — at risk of collapse Sunday night and prompting the evacuation of 185,000 people — could erode during heavy winter rains and cause a catastrophe.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
KaiserJeep wrote:The one fly in the pie is the damaged regular spillway. That might be an indication of poor maintenance, or a lack of necessary repairs during the drought years, as a result of state budget priorities.
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