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130,000 California Residents Ordered to Evacuate Below Endangered Dam Spillway
Roads leading out of Oroville, Calif., were jammed with traffic Sunday evening as more than 130,000 people were ordered to evacuate the area due to the possibility of failure of the alternate spillway at Oroville Dam, authorities said.
Butte County Sheriff Kory Honea said during a news conference Sunday night that he had no choice but to order the evacuation.
"I didn't have the luxury of waiting to see if all was OK. We need to get people moving quickly and to save lives in case the worst case came to fruition," Honea said.
"This is a very dynamic situation. This is a situation that could change very, very rapidly," he said.
Gaping Hole in Spillway for Tallest U.S. Dam Keeps Growing
A gaping hole in the spillway for the tallest dam in the United States has grown and California authorities said they expect it will continue eroding as water washes over it but the Oroville Dam and the public are safe. Earlier this week, chunks of concrete flew off the nearly mile-long spillway, creating a 200-foot-long, 30-foot-deep hole. Engineers don't know what caused cave-in that is expected to keep growing until it reaches bedrock. But faced with little choice, the state Department of Water Resources resumed ramping up the outflow from Lake Oroville over the damaged spillway to keep up with all the runoff from torrential rainfall in the Sierra Nevada foothills.
Officials said the critical flood-control structure is at 90 percent of its capacity. But the dam is still safe and so are Oroville's 16,000 residents. "The integrity of the dam is not jeopardized in any way because the problem is with the spillway and not the dam," department spokesman Eric See said.
Located about 150 miles northeast of San Francisco, Oroville Lake is one of the largest man-made lakes in California and 770-foot-tall Oroville Dam is the nation's tallest.
Source:
Oroville dam in California fails, mandatory evacuation of all residents ordered.
The Sacramento Bee reports that the emergency spillway of Oroville dam on lake Oroville in CA is in danger of imminent collapse. Lake Oroville is the largest drinking water reservoir in the US.
http://www.sacbee.com/news/state/california/water-and-drought/article132332499.html
(Score: 3, Informative) by bob_super on Monday February 13 2017, @08:52AM
The best that could be said about that is that just the emergency spillway failing would be worse than most regular dams. It's about 30 ft tall, and someone claimed each foot holds about 150 billion gallons of water (grain of salt, internet single source).
As of now, they have the water level below the emergency spillway, trying to bring the lake 50 feet down to get ready for upcoming storms this week, and do emergency repairs.
To do that, they're essentially sacrificing the bottom half of the normal spillway by sending 100000ft^3/s down into the gaping hole. Pictures should be interesting when the flow stops.
That amount of water isn't unusual for spring, so flooding shouldn't be too dramatic downstream. The emergency spillway does have the design capacity to allow a major flood in order to protect the dam itself, and that's if it doesn't collapse.
I saw a helicopter shot of the emergency spillway shortly before it crested, with crews pouring concrete between rocks added right under the wall. Hope it was quick-set.
(Score: 2) by VLM on Monday February 13 2017, @02:02PM
As of now, they have the water level below the emergency spillway
I'm too lazy to calculate it but they only have about half a GW of generating capacity at the base, given the size of the stream leading out on a normal day. Maybe it was low that day and its built for one GW. Whatever. Anyway my idea is installing ten times as much GW of capacity would be an interesting use of all that water rather than dumping it.
Or they could make the dam much taller. Yeah I know its already pretty tall.
It just seems energetically wasteful. You could electrorefine how much copper or aluminum with the water they're dumping?
(Score: 2) by dry on Tuesday February 14 2017, @03:20AM
How often do they dump the water? My local dam only wastes water by opening the extra sluices perhaps a dozen times a year most years, more this year. Not really worth the cost of extra turbines and generators even with a dam built for hydro. This dam is mostly for water storage so they probably dump water as little as possible