Published: Thu, February 16, 2017
Tech | By Arthur Brown

PJ Helicopters assists in emergency repairs on Oroville Dam

PJ Helicopters assists in emergency repairs on Oroville Dam

65,000 cfs of water flow through a damaged spillway on the Oroville Dam in Oroville, California, U.S., February 10, 2017.

The high water forced the use of the dam's emergency spillway, or overflow, for the first time in the dam's almost 50-year history on Saturday.

Sheriff Hornea said the plan is to use helicopters to drop bags of rocks into the crevice and prevent further erosion.

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.

In a July 2006 memo to managers, first reported by The Mercury News, a senior civil engineer with the agency's San Francisco office wrote that the agency determined dam safety "would not be compromised in the rare event of an emergency spillway discharge".

At 770 feet, Oroville is the tallest dam in the United States.

Wentz says evacuating acutely ill people is hard so it is usually better for them to stay where they are.

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The sudden decision on Sunday to evacuate tens of thousands of people was a departure from earlier assurances, when officials had stressed the Oroville Dam itself was structurally sound.

The evacuation was ordered Sunday after a massive hole was discovered in an emergency spillway - which catches excess water when Lake Oroville's water level rises to overflow the dam - threatening communities downstream.

Officials said the cities of Yuba City (Sutter County), with 65,000 people, and 12,000-population Marysville (Yuba County) across Feather River, were under mandatory evacuation orders.

It is the first time that Lake Oroville has experienced such an emergency in the dam's near 50-year history. "And on Saturday morning, it began pouring over there". To relieve pressure on the emergency spillway, water managers released water down the main spillway.

"Officials now anticipate a failure of the auxiliary spillway within 60 minutes", The National Weather Service said in a warning on Sunday afternoon, urging residents to evacuate in a northward direction toward the town of Chico.

Officials also worked to increase the amount of water being released from California's second-largest reservoir, as it was filled to the brim by rain and snowfall this winter after a six-year drought.

"We need to do everything we can to maximize our ability to move water our of this reservoir - not just for the coming storm but for the coming storms", said Bill Croyle, acting director of department of water resources. Since the hole opened up, the water from the dam has been flowing freely over the top of the dam.

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