Water & Drought

Expert: If emergency spillway collapses, Highway 70 corridor ‘is gone’

Streams of cars seen fleeing Oroville area

Sacramento Bee writer Dale Kasler seems to be the only car racing toward Oroville, as streams of cars are seen fleeing the Oroville area.
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Sacramento Bee writer Dale Kasler seems to be the only car racing toward Oroville, as streams of cars are seen fleeing the Oroville area.

The Sacramento Bee spoke with Joe Countryman, a member of the Central Valley Flood Protection Board and a former engineer with the U.S. Army Corps of Engineers ​for context on the engineering issues in the Oroville​ Dam crisis. Here​ is an edited transcript of the interview.

The Bee: What options does the state have given the situation at Oroville Dam?

​Countryman: You have very limited options. The only one right now is to increase the outflow from the dam.

The Bee: ​They have ramped up water releases to 100,000 cubic feet per second down the damaged spillway. What was the highest the main spillway ever ran​?

Countryman: ​In 1997 (during massive storms) it ran at 160,000 cfs.

The Bee: ​The dam is normally rated to handle that​, right?

Countryman: The leve​es that provid​e flood protection downstream ​can handle 150,000​ cfs​

The Bee: If the top ​of the emergency spillway ​goes, is that basically dam failure?

Countryman: It’s not going to be the (main) embankment failure, but it’s a failure. If it does happen, there’s nothing saying that the ground is going to stay where it is. That force of water will start tearing that hill apart​,​ and it could eat back into the reservoir and drain the reservoir.

The Bee: If that happens​,​ is it a “who knows what will happen?” situation?

Countryman: Yeah, it’s speculation, but most of the speculation would be it’s not good. It will be a helluva mess downstream. I think they’re taking the right action. I think between now and Thursday​,​ when the next storm arrives, they need to get the reservoir down as low as they can. Tomorrow, they need to start grouting the hell out of that embankment to try to shut off where that leak is.

The Department of Water Resources released a video shot by a drone over the Oroville Dam. Water is seen running over the emergency spillway as well as the main spillway.

The Bee: Say the top 30 feet of the emergency spillway does break off​,​ and it sends a pressure wave down the system​. That would raise concerns of levees failing in Oroville and other towns along the Feather River channel. ​Would it cause a big risk in Sacramento?

Countryman: ​It’s hard to say​, because there is a lot of volume in the floodplain, but once the levee burst​​ most of that water is going to be leaving the river and spreading across the land. With the Yolo Bypass and everything​, my gut tell tells me that Sacramento probably doesn’t have major concern.

The Bee: But Marysville, Oroville, Live Oak​? The Highway 70 corridor?

Countryman: That’s gone. I’ll tell you right now that’s gone. If they lose that 30 feet that’s gone.

The Bee: What happens tomorrow?

Countryman: ​You’ve got this dilemma: You’ve got a broken spillway that you don’t really want to be putting large flows down. But you don’t have any alternatives now. Now, you’ve got to put more water through it​, and you’re endangering (that structure). Tomorrow, when you wake up and we can get a good view of it​, you may see that those gates are in trouble. If they’re not – if they’re making this 100,000 cfs release (and) the gates are in a safe condition – then we’re in a pretty good position to ride it out.

The Bee: That means you can lean on the spillway full throttle?

Countryman: Exactly. And the channels can handle it. They were afraid to open it up because they didn’t know the broken spillway could handle it. Now they’ve been forced to open it up, and tomorrow we’l​l​ find out if it worked.

The troubled reservoir in Butte County is trying to release as much water as possible before new storms move into the region.

Ryan Sabalow: 916-321-1264, @ryansabalow

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