Helicopters cary huge bags full of rock to stabilize the emergency spillway next to the Oroville Dam on Monday Feb. 13, 2017, in Oroville, Ca.
Officials have ordered residents near one of the nation's biggest dams to evacuate the area, saying a "hazardous situation is developing" after an emergency spillway severely eroded.
But the fast-moving water also started breaking down the emergency spillway causing it to overflow.
The mandatory evacuation orders that have remained in place for two nights have been reduced to evacuation warnings near Lake Oroville, where erosion and threats of failure have plagued two spillways near the dam.
A massive hole has formed in the dam's spillway, and experts estimate fix costs could reach $200 million. The spillways, unused for half a century, failed to control the flooding and a large hole formed Sunday afternoon. Though many people think the Hoover Dam on the border of Nevada and Arizona is the tallest in the country, that honour belongs to Oroville.
Officials from the California Department of Water Resources are set to inspect an erosion scar on the spillway at the dam on Lake Oroville, about 150 miles north-east of San Francisco.
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Evacuation orders and advisories began Sunday around 4 p.m., eventually encompassing Oroville, Yuba City and other communities along the Feather River Basin. Rather than risk thousands of lives, Honea said, a decision was made to order the evacuations.
Dozens of federal aid workers were dispatched to the network of makeshift shelters where the almost 200,000 evacuated people, many of whom lived in Butte County, were spending their nights, waiting for word on when they could return home. Gridley and Live Oak were included in the evacuation alert on Sunday evening.
"Once this storm system arrives, Lake Oroville's water levels will rise, potentially forcing the need to utilize the failing emergency spillway", Brown added.
After requesting the evacuation of over 100,000 residents in Oroville and the surrounding towns, state agencies put in a request for PJ Helicopters to begin assisting on the stabilization project. As a result, the dam's primary spillway has been used heavily to accommodate the excess volume. It is unclear how far downstream potential flooding could occur if an emergency spillway at Lake Oroville fails.
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. This is expected to happen by late Saturday or Sunday, Croyle said.