Saturday, February 11, 2017

[californiadisasters] Lake Oroville overflows into emergency spillway

Lake Oroville overflows into emergency spillway

An aerial view Friday shows Oroville Dam to the right and the damaged spillway to the left. Just left of that is an area that crews started clearing Thursday for an emergency spillway, where water will course down the hill to the river below.

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The emergency spillway at Lake Oroville is needed after all, and water started flowing down a hillside north of the existing spillway this morning for the first time in the dam's history.

Friday afternoon, the state Department of Water Resources expressed confidence the emergency route would not be needed and even reduced flows down the existing spillway, which started crumbling during high releases on Tuesday.

But by this morning, the DWR said the emergency spillway would indeed be needed.

The emergency spillway isn't a spillway at all. It is just a hillside north of the spillway, starting in an area near the spillway boat launching ramp and parking lot.

The spillway has never been used for overflow since the dam was completed in the 1968.

Crews worked for two days with bulldozers to clear trees and debris near the top of the dam. They dumped rocks and poured cement in an attempt to create a course that will keep the emergency flow away from the existing spillway.

Once the water hits the dirt hillside lower down the ravine, however, it's expected to cause heavy sediment and erosion in the Feather River.

Though flows in the Feather River below are high, no evacuations are anticipated, officials have said continuously.

The lake is considered full when the surface is at 900 feet of elevation. The emergency spillway, a lip on the north end of the dam, is at 901 feet. At 8 a.m., the lake was at 901.09 feet, with 89,000 cubic-feet per second of inflow to the lake and 55,000 cfs going out.

The DWR continues to use the crumbling spillway to discharge 55,000 cfs but is also concerned about erosion to that structure.

"The emergency spillway flows are expected to wash large amounts of soil and debris into the Feather River," the DWR said in a press release, "and crews are positioned to remove as much debris as possible from the channel immediately downstream of the dam."

The DWR also said downstream flows in the Feather River were well within the carrying capacity of the levee system.



Posted by: Kim Noyes <>

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