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Hole in California Dam Continues to Grow

Emergency spillway being prepared

February 10, 2017

The California Department of Water Resources tweeted this morning that the flows from the Oroville Dam spillway have reached 65,000 cubic feet per second.

Tuesday, chunks of concrete flew off the nearly mile-long spillway, creating a 200-foot-long, 30-foot-deep hole on the tallest dam in the United States. The water flowing out of the hole quickly turned brown with mud as it consumed trees and soil before rejoining the main channel below in a massive confluence wave that sent up clouds of mist in the tree-lined canyon. Engineers don't know what caused cave-in that is expected to keep growing until it reaches bedrock.

UPDATE: Spillway is expected to fail

Located about 150 miles northeast of San Francisco, Oroville Lake is one of the largest man-made lakes in California and 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.

In preparation for the potential use of the emergency spillway, DWR has been clearing trees, rocks, and other debris from the hillside near the 770-foot-tall dam where water will flow.

The lake was rising at a half-foot per hour Thursday as the inflow peaked at 121,000 cubic feet per second, officials said at a news conference about a mile from the spillway. They were releasing water at about 40,000 cubic feet per second.

That's not enough to keep the lake from continuing to rise, officials said, but is expected to keep them from having to use a nearby emergency spillway that has never been used since the dam was dedicated in 1968.

As a backup plan, state workers and contractors were pulling out trees and bushes by the roots from the emergency spillway to keep them from floating downstream.

"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.

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