Monday, February 13, 2017

‘NOT a drill': 188,000 evacuated, emergency declared, as Calif’s massive Oroville Dam threatens floods

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. Even as they fled, however, the flow of water over the spillway halted late in the evening, stabilizing the crisis. But officials warned the damaged infrastructure could create further dangers as storms approach in the week ahead and it remained unclear when residents might be able to return to their homes. 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. After a record-setting drought, California has been battered by potentially record-setting rain, with the Northern California region getting 228 percent more than its normal rainfall for this time of year. The average annual rainfall of about 50 inches had already been overtaken with 68 inches in 2017 alone. There was never any danger of the dam collapsing. The problem was with the spillways, which are safety valves designed to release water in a controlled fashion, preventing water from topping over the wall of the colossal dam that retains Lake Oroville. 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...more

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