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188,000 people under evacuation after Northern California dam spills (VIDEO)

188,000 people under evacuation after Northern California dam spills (VIDEO)At least 188,000 people remain under evacuation orders after Northern California authorities warned an emergency spillway in the country's tallest dam was in danger of failing Sunday and unleashing uncontrolled flood waters on towns below.

This is reported by Associated Press.

About 150 miles northeast of San Francisco, Lake Oroville is one of California's largest man-made lakes, and the 770-foot-tall Oroville Dam is the nation's tallest.

The evacuation was ordered Sunday afternoon after engineers spotted erosion on the dam's secondary spillway. The cities of Oroville, Gridley, Live Oak, Marysville, Wheat land, Yuba City, Plumas Lake, and Olivehurst were all under evacuation orders.

The evacuation order went out around 4 p.m. after engineers spotted a hole that was eroding back toward the top of the spillway.

The erosion at the head of the emergency spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville, the California Department of Water Resources said. Those potential flows could overwhelm the Feather River and other downstream waterways, channels and levees.

Officials say Oroville Lake levels had decreased by Sunday night as they let water flow from its heavily damaged main spillway. Late Sunday, officials noted that water levels had lowered enough that water was no longer spilling over the eroded area.

Water began flowing over the emergency spillway at the Oroville Dam in Northern California on Saturday for the first time in its nearly 50-year history after heavy rainfall. Officials earlier Sunday stressed the dam itself was structurally sound and said there was no threat to the public.

The California Department of Water Resources said it is releasing as much as 100,000 cubic feet per second from the main, heavily damaged spillway to try to drain the lake.



Department engineer and spokesman Kevin Dossey told the Sacramento Bee the emergency spillway was rated to handle 250,000 cubic feet per second, but it began to show weakness Sunday at a small fraction of that. Flows through the spillway peaked at 12,600 cubic feet per second at 1 a.m. Sunday and were down to 8,000 cubic feet per second by midday.

Unexpected erosion chewed through the main spillway during heavy rain earlier this week, sending chunks of concrete flying and creating a 200-foot-long, 30-foot-deep hole that continues growing. Engineers don't know what caused the cave-in, but Chris Orrock, a spokesman for the state Department of Water Resources, said it appears the dam's main spillway has stopped crumbling even though it's being used for water releases.

The lake is a central piece of California's government-run water delivery network, supplying water for agriculture in the Central Valley and residents and businesses in Southern California.
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