Evacuation Ordered For Low Levels Of Oroville, Auxiliary Spillway Expected To Fail

• Feb. 14 UPDATE: Work On Oroville Emergency Spillway Continues, Evacuation Orders Still In Place
• Feb. 13 UPDATE: Water Levels Drop At Lake Oroville, Evacuations Remain In Effect

UPDATE 5:26 p.m. Feb. 12: Orovillle residents are being ordered to evacuate Sunday. Officials say the auxiliary spillway at the dam is expected to fail. Read updates here.

UPDATE 11:03 a.m. Feb 12:  The California Department of Water Resources says water levels are "trending down" in Lake Oroville, where water has been flowing since early Saturday down an emergency spillway being used for the first time in the history of the reservoir.

The department says water flows over the spillway peaked at 12,600 cubic feet per second at 1:00 a.m. Sunday.

The DWR reiterated in a press release Saturday evening that the flow over the spillway was "extremely low" compared to its capacity, and that the situation posed no threat to downstream communites or to the dam.

As of Saturday another 55,000 cubic feet per second of water was still being released down the main spillway, which was operating at lowered capacity due to major erosion.

The DWR said it was focusing on ways to get the Hyatt Power Plant at Oroville Dam back online, because it can release 14,000 cubic feet per second once in operation, taking pressure off the spillways.

Here is an aerial view of the spillway provided by CA DWR from Saturday, January 11:

UPDATE 10:57 p.m. Feb. 11:

UPDATE 2:18 p.m. Feb. 11: The California Department of Water Resources is expecting flows over the Lake Oroville emergency spillway -- also referred to as its auxiliary spillway -- to last less than three days, says Eric See, a DWR environmental program manager speaking on behalf of the agency at a Saturday afternoon press briefing. Flow over the spillway began around 8 a.m. Saturday. This is the first time in history the emergency spillway has ever been used.

At some point in the next 38 to 56 hours, See says, inflow to the lake should drop enough that the emergency spillway is no longer needed. He says the estimated outflow from the spillway is expected to range from 6,000 to 12,000 cubic feet per second during that time.

DWR Acting Director William Croyle said at the briefing that the current priority is to prevent sediment and debris at the base of the spillways to cause water to back up into the power plant at the base of the dam.

Croyle says an additional concern is making sure that erosion does not impact an electric tower that connects to the dam and sits adjacent to the damaged main spillway. The power plant is currently not in operation, and is not designed to allow water to flow while offline. Once the power plant can come back online, Croyle says, releasing water through the dam itself will help lower the lake level.

UPDATE 9:27 a.m. Feb. 11: Water is flowing through an emergency spillway at Lake Oroville, the first time since the nation’s tallest dam was built. California water managers continue to emphasize that the volume of water poses no imminent flood threat downstream and should remain well within the capacity of the Feather River and other channels to handle. 

The California Department of Water Resources says it has been preparing to use the emergency spillway since Tuesday, when erosion opened a gaping hole in the concrete gated spillway typically used in winter. Officials say the 95,000 cubic feet per second inflow to the lake exceeds the discharge that the regular spillway can handle.

Original Post, Feb. 10: The California Department of Water Resources says there will likely be no need to use an emergency spillway at Oroville Dam to keep the lake from overflowing.

Water flowing into Lake Oroville has been decreasing steadily and the main spillway is still releasing 65,000 cubic feet per second of water despite a gaping hole about halfway down the concrete chute.

As for the cause of the damage to the spillway, Kevin Dossey with DWR says the spillway is inspected by local, state and federal agencies.

"We have three different inspections going on every year," he says.

Inspectors tap the concrete with a chain to hear voids underneath.

"We find voids under it and then they make repairs as necessary. It's common for spillways to develop voids because of the drainage system under them," he says. "Some of the spillway was constructed on good, strong bedrock and that's the part up above that we're confident it won't erode."

But halfway down is a different story.

"We've seen the hole as deep as 45 feet deep and I would think we would need to slurry that in with concrete fill," he says. "That's a big engineering project that's going to have to get done rapidly as soon as the inflows reduce in the spring."

Cement trucks have been pouring concrete at the mouth of the emergency spillway since Thursday. It had previously been a simple dirt channel.