Thousands in California told to evacuate amid fears of flooding at Lake Oroville

Large-scale evacuations are taking place among residents of the low levels of Oroville and areas downstream after torrential rains led to the overflow of Lake Oroville in Northern California for first time in 48-year history, leading to what is said to be an imminent failure of the dam’s spillway, which according to officials could “lead to a failure of the structure.”

Officials said a hazardous situation is developing with the Oroville Dam auxiliary spillway. The operation of the auxiliary spillway has led to severe erosion that could lead to a failure of the auxiliary spillway.

Aerial view from the California Department of Water Resources.

According to Fox 40, failure would result in an uncontrolled release of flood waters from Lake Oroville. The DWR is increasing water released to 100,000 cubic feet per second. Furthermore, use of the auxiliary spillway has lead to severe erosion that could lead to a failure of the structure, causing unprecedented flooding and damage.

The authorities in Northern California raced to evacuate tens of thousands of people on Sunday night in fear of the possible failure of an emergency spillway at the Oroville Dam.

Despite concerns of an imminent breakdown earlier in the night, officials said late Sunday that the water level at the Lake Oroville reservoir had dropped, halting water flow over the emergency spillway and temporarily stabilizing the situation.

The National Weather Service has issued a flash flood warning for possible dam failure.

Still, officials were concerned about the integrity of the emergency spillway, and more than 100,000 people were evacuated from Butte and Yuba Counties.

Gov. Jerry Brown warned late Sunday that the situation was “complex and rapidly changing” and directed the deployment of state resources to the area to deal with “this very serious situation.”

Areas affected include Oroville, Palermo, Gridley, Thermalito, South Oroville, Oroville Dam, Oroville East and Wyandotte. An evacuation center for residents has been set up at the Silver Dollar Fairgrounds at 2357 Fair Street in Chico.

The relatively light flow of water that began washing into Lake Oroville’s auxiliary spillway Saturday morning is expected to continue flowing for the next few days. Total releases from the reservoir do not threaten the dam or downstream communities and fall well within the capacity of the Feather River and other downstream channels.

Hampered by serious erosion that opened starting Tuesday on the lower portion of the dam’s main spillway, the California Department of Water Resources (DWR) prepared for Lake Oroville to rise to its highest level ever.

Residents leaving Carlifornia:

It's gridlock in Yuba City where highways 20 and 99 come together. Photo from @selljo_ , who's stuck in it. pic.twitter.com/IFe7teA1Ni

— David Little (@DavidLittleNVCF) February 13, 2017

The lake exceeded the elevation of 901 feet above sea level shortly after 8 a.m. today, at which point water slowly began to flow over the concrete weir of the auxiliary spillway, down a hillside, and into the Feather River. The auxiliary spillway is operating as intended.

“The flows we’re seeing are extremely low compared to the design of the structure,” said DWR Acting Director William Croyle. Based on our current situation, there is no threat.” Flows of between 6,000 cubic feet per second (cfs) and 12,000 cfs are expected to flow into the auxiliary spillway for 32 to 58 hours, based on the latest modeling of weather, reservoir inflow and other factors. Those flows will stop once discharge from the lake exceeds inflow.

Flows into the auxiliary spillway are far less than the volume of water washing into the lake from the Feather River watershed. That’s because the 16,000-acre surface of the lake acts as a buffer, spreading and attenuating inflow. In order to help manage reservoir levels, DWR operators also are discharging 55,000 cfs from the damaged concrete spillway and expect to continue to do so. Upward erosion on this closely monitored, gated spillway has slowed considerably.

DWR focused Saturday on ways to get the Hyatt Power Plant at Oroville Dam back in operation, because 14,000 cfs can be discharged from the plant when it is operating, which would help with reservoir management. Power generation was halted when the water levels in the channel that leads from the power plant became high enough to compromise operation.

Water levels rose when debris from the eroded concrete spillway piled up in the channel below. The same erosion also threatens the towers that hold the power lines that take electricity from the power plant to the electrical grid; such a connection is needed for the power plant to operate. DWR, Pacific Gas & Electric Company, and other partners are working to safeguard the hydroelectric facility and power lines.