DWR discusses first-ever water release from Oroville Dam emergency spillway

Photo Courtesy of The California Department of Water Resources.

OROVILLE, Calif. - The California Department of Water Resources (DWR) hosted its first news conference since water went over the emergency spillway on Saturday. It's the first time water has ever been released from this area of the Oroville Dam in the facility's 48 years of existence.

"This is a very unusual event for us here in Oroville, to actually have water flowing over this weir," DWR spokesperson Eric See.

Water at the Oroville Dam reached 901 feet around 8 a.m. Saturday, causing the water to run uncontrolled over the emergency spillway, which is a dirt hillside to the left of the damaged regular spillway. As of 1 p.m. Saturday, the lake level continued to increase. The lake was at 901.80 feet, with 77,475 cubic feet per second (cfs) coming into the lake, and 55,082 cfs being released.

Bill Croyle, acting director of the DWR, gave an update on the dam and the spillway and then answered questions on Saturday. The key points that Croyle wanted to get across were that Oroville Dam is in no danger of being damaged or failing and that there is currently no risk of flooding downstream.

He said the department bases its decisions on models every six hours.

"When we went home it was raining pretty hard. Those kinds of events - I'm not saying that's what caused it, but the change in weather conditions have a dramatic impact on the inflow to the reservoir upstream, and how that inflow is routed through the reservoir system," Croyle said.

Croyle focused on the flow of water coming out of the main spillway, a rate of 55,000 cfs for most of Saturday, and the emergency spillway, which is estimated to be 6,000 to 12,000 cfs. While talking about possible flooding he cited previous years where more water was in the Feather River without flooding occurring downstream.

Croyle also talked about how as of Saturday morning, the water coming off of the main spillway is now clear and that this means erosion, which was caused by the broken spillway, had mostly stopped.

PG&E spokesperson Denny Boyles said crews took down three spans of power lines Friday, and were planning on taking down two towers by the spillway to limit debris being washed into Feather River. However, it was unsafe for crews to work on them once the water started going through the emergency spillway.

With a storm coming in later this week, the DWR will be trying to reduce the size of the lake behind the dam to open up room for the coming rains. In the coming months, the DWR will continue to look for atmospheric rivers forming that could dump a large amount of water into the lake in a short period of time which would recreate the issues seen in the past week.

Looking forward, the DWR says another concern is the high level of snow pack that has blanketed northern California.

A new area of focus in the DWR press conference was that of the hydroelectric power plant that sits at the base of the dam. The plant, which can allow for a small amount of water to be released through the dam, is currently shut down. In its current state, no water would pass through putting more pressure on the spillway system.

While operating, the plant can push through 14,000 cfs of water which would help with reservoir management. The power generation was halted when water levels in the channel rose too high and comrpomised operation.

According to Croyle, the plant faces two challenges. First, if debris washes upstream and gets into the plant it could damage equipment and cause them to shut down operations. Second, if the power lines that connect the plant to the grid go offline then the plant is no longer able to operate, or even let water through. Currently, the power lines are stretched across the area where the emergency spillway is releasing water, and erosion could damage the power poles.

PG&E had been doing preparatory work on the lines in the past couple of days, but with water coming off the emergency spillway it became no longer safe for them to continue their work and they had to back off. A spokesman for PG&E said that they are working closely with the DWR to monitor this issue.

Croyle estimated the cost of repairing or replacing the damaged spillway could cost from $100 million to $200 million.

He also said the department is not concerned about flooding or evacuations.

"The flows that we're seeing from whatever source out of the dam right now are less than a half of what we normally see in a really tough flood event that would stress our systems. So there's no reason in my opinion, based on the information we have now, which is available to you, that we should be worried about evacuating any part of this region," Croyle said.

Aerial footage shows water flowing over emergency spillway at Northern CA's Oroville Dam, the nation's tallest dam

-- ABC News (@ABC) February 11, 2017
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