Roughly 200,000 residents have been evacuated from the towns below Lake Oroville in Northern California because of erosion damage to the dam's auxiliary spillway. If a wall at the top of the spillway gives way, the result would be massive flooding in the regions below the lake.
Brad Alexander, Chief of Media Relations for the Governor's Office of Emergency Services, says the second spillway is designed to relieve pressure on the dam when the lake rises to a dangerous level.
"They started using it a couple days ago slowly and then things escalated yesterday with a lot heavier flows and there was a concern they'd have an uncontrolled release of water," he said.
Alexander notes this is the first time water has run out the auxiliary spillway since the dam complex was constructed in 1986. "And since it's never been used before," he said, "it is sort of unexplored ground for the engineers that are up there."
The Oroville dam is an important part of California's water infrastructure. Is what's happening there an isolated incident, or just the most visible symptom of an entire system that is aging and in need of repair?
Jeff Lund is Director of the Center for Watershed Sciences at UC Davis. He answered these key questions about Oroville, and the water system in general.
Where Oroville fits into our state's water supply?
Lake Oroville is our major water storage for the state water project which is about 1/3 of the water supply for Southern California. It's the largest earth-filled dam in the United States.
The spillway is some distance from that earth-filled dam so there's no likelihood for the dam to actually fail. But its really just the top 30 feet or so of the emergency spillway that we are most worried about.
How is our water infrastructure in kept in shape year-round?
We should always have a good reserve fund. We should always be inspecting them and looking for ways to improve them. This is just a reminder of what happens when you stress these systems either with floods or droughts.
With floods you have to worry about a little but more catastrophic outcomes and we are seeing that potential here. We are in the middle of what is so far, the wettest year on record over more than 100 years. We should be seeing some strains. This is the kind of thing you expect to see and we need to be prepared for these kind of events.
What should we be doing to prevent floods, even when the weather is dry?
They have been doing inspections on the flood control systems. In fact, I think the flood control system as a whole (it's really the levy systems) are in better shape than they've been over the last 50 years or so. As we get more and more people in California, we have more and more reasons to pay attention to these sorts of things.
How would you rate, or characterize the status of our water systems?
Most of the systems for the big state water project, they were built in the 50's and 60's. So, there's getting fairly old. That doesn't necessarily mean that they're not working as well. A lot of the mechanical parts; the turbines, the gates, the pumps... those are the things we really need to start worrying about replacing. And then of course, keeping the spillways inspected and upgraded from time to time as well.
What needs to be done to improve the infrastructure across the board?
I think the flood control system is always a chronic problem because we don't have a very good funding model for handling it. We tend to fund it in big lumps, in big bonds, but we don't have regular finding for it year in and year out which what you really need to do pay attention to these things.
I think for that damaged spillway, there's going to have to figure out a way to rebuilt it fairly fast. Depending upon what the bedrock that they find down below it, it'll lay out different options that they have. I'm mostly worried about the next couple of months.
*Quotes edited for clarity*
To hear the interviews with Brad Alexander and Jeff Lund, click on the blue Media Player arrows above.
Correction: An earlier version of this story incorrectly identified Lake Oroville. KPCC regrets the error.