OROVILLE, Calif. (AP) - The Latest on problems with an emergency spillway at the nation’s tallest dam (all times local):
7:30 p.m.
A report prepared for crews responding to damage at a Northern California dam suggests rain may have contributed to a massive crater in the main concrete spillway for Lake Oroville.
An “incident status summary” prepared by a CalFire official on Saturday says the spillway “was compromised during heavy rains.” It says water was diverted toward the hillside next to the spillway, undermining the concrete structure and causing a portion to collapse.
The spillway damage caused a series of events that led authorities to order nearly 200,000 people to evacuate Sunday.
CalFire spokesman Richard Cordova says the document is an internal status update issued every 12 hours. It was first published by the Los Angeles Times on Thursday.
Cordova says complete cause of the damage is still unknown.
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1 p.m.
Officials monitoring the stricken Oroville Dam in Northern California say they’re confident the damaged spillway and eroded hillside can withstand approaching storms.
Department of Water Resources Acting Director Bill Croyle said Thursday that officials identified three areas where erosion caused the most concern about potential flooding.
He says one area has been 100 percent repaired, while the others were 25 percent and 69 percent fixed.
Croyle says officials are reducing the amount of water released from the lake, but he still expects the level to continue falling through the duration of storms forecast in the coming days.
With less water flowing down the dam’s spillway, officials hope to clear debris that threatens a hydroelectric power plant at the base of the dam.
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12:10 p.m.
California officials are slowing the release of water from a lake behind the nation’s tallest dam so crews can remove debris from the bottom of the structure’s damaged spillway.
State Department of Water Resources officials said Thursday that removing debris protects Oroville Dam’s power plant and will allow for it eventually to be restarted.
Officials had been releasing 100,000 cubic feet of water, or enough to fill an Olympic-size swimming pool, each second from the lake since Sunday, when the sheriff ordered an immediate evacuation. They didn’t say how much water is now being released.
Department acting Director Bill Croyle said Wednesday that water managers would start dialing back the flow now that the lake has been reduced and can absorb runoff from storms expected over the next several days.
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10:35 a.m.
The American Red Cross continues to feed and shelter some 1,500 people in Northern California where authorities have lifted the mandatory evacuation order for almost 200,000 people near the Oroville Dam spillway.
While the risk has been reduced, the region is expected to see several inches of rain in the next few days. Red Cross workers will remain in place in the event that anyone has to evacuate again.
Last week, the Department of Water Resources discovered a massive crater in the concrete-lined spillway.
Later, the emergency spillway was used. But erosion began to progress up the right side, prompting authorities to order an evacuation of 188,000 people. Most have returned home.
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10:10 a.m.
California officials say the water level at Lake Oroville is 32 feet below its dam’s damaged emergency spillway.
For a third day, the state Department of Water Resources says dump trucks and helicopters are dropping thousands of tons of rocks and sandbags to shore up the spillway at the Oroville Dam, the nation’s tallest.
It says barges and cranes are being mobilized to remove debris and sediment from a diversion pool.
The department says about 100,000 cubic feet of water was flowing from the reservoir each second, enough to fill an Olympic-size swimming pool.
Weather forecasts call for 2 to 4 inches of rain and snow in the foothills and mountains near the dam. But the storm was expected to drop less rain and create less runoff than drenching storms from last week.
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8:25 a.m.
The critical document that determines how much space should be left in Lake Oroville for flood control during the rainy season hasn’t been updated in 47 years.
The Sacramento Bee reports (https://bit.ly/2kUEn66 ) the outdated document uses climatological data and runoff projections that don’t account for two past floods.
Independent experts familiar with the flood-control manual at Oroville Dam say there’s no indication the outdated document contributed to the ongoing crisis involving the dam’s ailing spillways. Structural failures are the trouble.
But experts say the manual points to larger operational issues that affect most of California’s primary flood-control dams.
Last week, the Department of Water Resources discovered a massive crater in the concrete-lined spillway.
Later, the emergency spillway was used. But erosion began to progress up the right side, prompting authorities to order an evacuation of 188,000 people.
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