
Water from Lake Oroville flowed over the emergency spillway at Oroville Dam for the first time in the reservoir's 48-year history after the water level exceeded 901 feet in elevation shortly after 8 a.m. today.
The water slowly began to flow over the concrete weir of the auxiliary spillway, down a hillside and into the Feather River, a major tributary of the Sacramento River, the state’s largest river.
The flow over the auxiliary spillway has been between 6,000 and 12,000 cubic feet per second, according to an update from the California Department of Water Resources at 10:14 am on February 11.
Agency officials expect these flows to go into the auxiliary spillway for 32 to 58 hours, based on the latest modeling of weather, reservoir inflow, and other factors. There is no danger to the dam or people from the flows, according to the Department of Water Resources.
In a news briefing today, DWR Acting Director William Croyle said dealing with the damage caused by the growing hole in the dam's primary spillway could cost 100 to 200 million dollars.
Croyle said the damaged spillway will need complete replacement, noting that the current structure is not viable.
The flows we’re seeing are extremely low compared to the design of the structure, said Croyle. Based on our current situation, there is no threat.
In a statement earlier today, DWR said the volume of water is expected to pose no flood threat downstream and should remain well within the capacity of the Feather River and other channels to handle. Oroville Dam itself remains safe, and there is no imminent threat to the public.
The emergency spillway has not been used since the dam was finished in 1968, but DWR has anticipated and prepared for its use since Tuesday, when erosion opened a cavity on the concrete, gated spillway typically used in winter operations at Lake Oroville. DWR continues to use that damaged spillway to discharge 55,000 cubic feet per second, but the approximately 95,000 cfs inflow to the lake exceeds that discharge. As of 4