From the Department of Water Resources press conference, here are my notes from what Bill Croyle, Acting Director of DWR had to say:
Water has stopped flowing over the emergency spillway. Increasing the flow from 55,000 cfs to 100,000 cfs down the main spillway has taken the head off the auxiliary spillway; this was done to reduce and stop the erosion. They have done a visual inspection from the air in detail and have developed contingency plans. They will address things on the ground in the morning. Resources being brought into the area.
They are sensitive to the condition of the damaged spillway but they also need to draw the reservoir down. Right now, inflow is 40,000cfs, outflow is 100,000 cfs. They need to draw the reservoir down to make room for anticipated storm later this week.
If they can keep discharge rate up and not compromise the damaged main spillway, they can move out 1.2 MAF in a day. They need to drop the level in the reservoir 50 feet to get to the normal operating level given the type of hydrology this year.
The goal is to keep discharges up as high as possible. They want to maintain the system at a rate that doesn’t further degrade the infrastructure that they have as they will need to continue to use it throughout the rest of the wet season.
A flow of 100,000 cfs is typical for this time of year. The river channel through the Oroville area is capable of 150,000 cfs. If the flows stay between 75,000 – 130,000 cfs, it’s well within the flood control system for this area.
The evacuation orders will not be lifted at this time. They need to assess the situation further.
Here is more from Bill Croyle:
“The integrity of the dam is not impacted by the damage to the spillway itself or the use or the erosion that’s occurred at the emergency spillway, and so the dam is solid. The control structure has been damaged. We’re working to assess that, and we’re already working on the redesign and recovery of that system before next year, but right now, we’ve had some wet weather, we’re going to have some more wet weather, and the idea is to manage our resources, our physical resources and managing those flood flows here for the next couple of months.”
“We want to go back in, complete our assessments, do our corrective measures on that emergency spillway, and get it ready for the potential for a future use here in the coming weeks or months.”
“The event starting last Tuesday has thrown a lot of curves at the group of various agencies that are working on this. Once you have damage to structure like that, it’s catastrophic. Part of that is what can we do in a very short period of time. We determined we could not fix the hole, it was 250 feet long, 170 feet wide, and almost 40-50 feet deep. You don’t just throw a little bit of rock in it, and then a few hours later want to throw 60,000 – 100,000 cfs at it, so once we worked through the math and looked at our available resources and how long we would need to keep the chute dry until we actually got it fixed, it was realized we couldn’t repair it.”
“We knew that we’re going to see new damage. What you see today might not be what you see tomorrow. This last 24-36 hours, the site had stabilized. The erosion downstream of the spillway is kind of stabilized; there are some things that we’re worried about in implementing our contingency plans, but we had some hydrology come in a little wetter and the storm system parked over this region of California a little longer, so we had a forecast, we were operating to that forecast, and it came in a little wetter, so we took some water over the emergency spillway.”
“Our goal is to be able to use that infrastructure throughout this wet season. So we don’t want to put too much water down it at any given time, so we want to maintain the integrity of that system.”
“If there’s additional erosion on the spillway itself, we’ll reduce the flow, assess. We’re already developing additional contingency measures to … implement a corrective measure to protect the end of the spillway where the water falls off … we have developed that strategy and soon we will have those materials on site, should we decide we need to deploy that.”
As always, you can count on Maven’s Notebook to continue to keep you informed as this situation continues.