A lot has happened at Lake Oroville in the three days since I posted an introduction to the State Water Project (SWP), to put it mildly.
At the time of that writing, Saturday afternoon, the lake level was at 902.02’, with water flowing over the emergency spillway sill at 901’, and releases from the damaged controlled spillway at 55,000 cubic feet per second (cfs). The lake level peaked at 902.59’ at 3am Sunday morning and then began to slowly decline. At 11am Sunday, the California Department of Water Resources (DWR) reported that flow over the emergency spillway had peaked at 12,600 cfs and since declined to 8,000 cfs, with the situation stabilized. At 4:40pm Sunday, an emergency evacuation was ordered, with the emergency spillway predicted to fail in as soon as an hour.
This photo from February 11 shows the emergency spillway not long after water began to flow over it. Note the roadway in front of the spillway. Very little erosion has occurred in this photo, though some channelization is visible bottom center.
This photo from February 12 shows the emergency spillway with erosion having progressed further uphill. Note the road has been washed out, and the channel has deepened and worked its way uphill.
Faced with this situation, DWR increased the releases from the controlled spillway, to try to save the emergency spillway. Releases were increased to 100,000 cfs, and after a few very tense hours, the lake level dropped below 901’ at about 8pm Sunday. Water stopped flowing over the emergency spillway, and the erosion stopped.
This photo from February 13 shows the damage to the emergency spillway. Note the people for scale. I do not know which channel was of the most concern but the large channel near the washed out road and white truck was not the closest to the emergency spillway sill. Top right, just left of the far end of the concrete spillway, are two workers in yellow vests standing by the channel that got closest. This photo shows a closer view, with that channel just behind the workers.
It’s obviously a huge relief that the lake level is below the emergency spillway and that the structure survived. It’s also a huge relief that the damaged controlled spillway has been able to maintain 100,000 cfs releases, which as of this writing (9pm February 14, 2017) have lowered the lake level to 883.60’, over 17’ below the surface of the emergency spillway sill.
This has allowed DWR to being making emergency repairs to the emergency spillway, in case it must be used again. This photo shows placement of rock in the channel that got closest to the emergency spillway sill. DWR also posted two videos, one from yesterday and one from today, showing the repair work. Emergency evacuation orders have been lifted, but residents are to remain vigilant under an evacuation warning, in case the situation changes.
It is very good news indeed that the emergency spillway survived. However, it is only mid-February and we still have a lot of winter to go, followed by spring runoff when an above-average snowpack melts. In another stroke of good fortune, the National Weather Service (NWS) Sacrament office is predicting the next storm, for Wednesday night and Thursday, to have lower snow levels (5000’-6000’) than originally expected (7000’-8000’). This will keep the precipitation as snow, rather than rain and melted snow that will immediately run down into Lake Oroville. This will allow DWR to keep lowering the lake level to create flood storage for the spring, and keep making repairs on the emergency spillway. Another series of storms is expected for Monday and Tuesday next week, but with snow levels between 3500’-5500’.
After the snow is gone, there are going to be a lot of questions to be answered. I’m not going to litigate the decisions made by DWR here; I’m sure there will be plenty of people to do that soon enough. I also want to say that I have great respect for the many DWR engineers and workers, the Butte County Sheriff, and many other public employees and safety officials that have worked hard to ensure public safety, and have had to make many extremely difficult decisions about how to proceed in a dangerous and dynamic situation.
As a civil engineer, things like this really hurt. Like many civil engineers, I went into this business because I believe it is a profession where I can put my natural skills to work in a way that improves people’s lives. I never want to see our works fail or put people at risk.
This is going to be a case study for future civil engineers, for that is what we must always do when something doesn’t work the way it should: ask ourselves why, figure out what went wrong, learn from it, and improve our designs and processes so that we increase public safety and public benefits in the future. I think there will be four main questions to be researched here:
- What was the proximate cause of the damage to the controlled spillway?
- Why was the emergency spillway damaged so critically by relatively modest flows (12,600 cfs) relative to its capacity (several hundred thousand cfs)?
- What was the decision making process after the initial damage to the controlled spillway? Was all relevant information available to decision makers?
- Was information available before the crisis that should have led to corrective actions, and if so, what stopped corrective actions from being taken?
In short there are several distinct things here: pre-crisis actions, controlled spillway damage, emergency spillway damage, and crisis management.
Again, none of this is to question the hard-working people who are doing everything they can to mitigate the crisis and have faced very difficult decisions. As engineers, we must seek to improve our understanding of our designs, how the natural world interacts with our designs, and how our decisions and processes affect those systems. My heart goes out to anyone affected by this situation, and I sincerely hope that we, as Californians, can pull through this and use the lessons to help make our state a better place.