Here is Wednesday morning’s installment of our update on the Oroville Dam spillway incident and more news about the valley. For background, please see our earlier blog posts which set the stage and provide context. In sum, the mandatory evacuation is over; the emergency or auxiliary spillway remains stable; workers continue to add rock and concrete to address the erosion that led to the evacuations; the primary or service spillway is also stable, and is still evacuating 100,000 cfs from the reservoir; but new storms are forecasted to roll in starting Wednesday evening.
Because there is less news today, we have tried to provide some information on the weather and flood system operations. As always, if you find this blog helpful or interesting, please feel free to share it with others who may be interested. And if you would like to be updated when we post a new entry, please add your email on the right where it says “stay connected.”
1. At 1:00 on Tuesday the mandatory evacuation was lifted. According to the authorities, the goal was to not end the evacuation until the authorities felt confident that a new evacuation would not be immediately necessary. As noted yesterday, DWR had stated that the evacuation order would end when “we can be 100 percent assured that they can stay back in their homes.”
2. Water in Oroville Lake continued to drop throughout Tuesday, and was projected to be down to 880 feet by sunrise Wednesday morning (remember that the lip of the emergency spillway is at 901 feet). Outflow from the primary spillway remained near 100,000 cfs. The lake had fallen about twenty-two feet since Sunday afternoon and approximately a quarter of a million acre-feet of water had been released. As of Tuesday night, the lake was draining at about a foot every two hours. Due to the shape of the reservoir, this was faster than the rate on Monday, which was about a foot every three hours.
3. We now know that DWR has been working hard to fill the crater that formed at the base of the emergency (or auxiliary) spillway. This photograph comes to us from the LA Times, which credits the infographic photo to DWR, Google Earth, and detail image courtesy of AFP Getty. It does a great job of showing the layout of the various facilities, where the rock is being dumped and where the concrete is being pumped. Unfortunately, there are very few photographs we have been able to find of the actual work taking place. We have elected to skip reprinting the photos and videos of helicopters flying with bags of rock in tow.
This second un-credited photo from the LA Times shows the concrete being pumped into the crater. According to the Sacramento Bee, the Department of Water Resources said late Tuesday that 125 crews are working around the clock to place 1,200 tons of material per hour on the spillway.
4. More rain is headed to Northern California starting Wednesday.
DWR indicates that anticipated flows into Oroville from this set of storms should be lower than the flows from last week’s storms – but those flows were significant. Here is a graphic from the National Weather Service showing the expected rain fall. It is important to note that many of the storms this season have dropped more water than predicted.
Here also is the seven day rainfall forecast for the region from the National Weather Service. You can see that while the rainfall is significant, it is not as large at the recent storms we have weathered. The issue for DWR and the downstream communities is whether the primary spillway will be able to continue to drain the lake at the current levels through the rest of the rainy season.
5. We have not located any additional information regarding the claim that DWR and the State Water Contractors rejected requests or demands to armor the slope downhill of the emergency spillway. For that reason, we will avoid conjecture but will update you when we have more facts.
6. The President approved a request from Governor Brown to declare a State of Emergency for Sutter, Butte, and Yuba Counties.
For more detailed information about current storage, inflow, and outflow from Oroville Dam, we still recommend the California Data Exchange Center. Additional sources of information on this incident can be found on the DWR website and DWR has shared this phone number for public updates: 530-872-5951.
As we did yesterday, we also wanted to again acknowledge that the Oroville spillway is not the only challenge being faced by the Central Valley of California. Very high river flows in this very wet year have strained many of the rural levees in the valley. Flood fighting is currently going on in districts on both the east and west sides of the Feather River. And as the higher releases from Oroville find their way downstream, we expect to hear of more stress on Delta levees. This additional flow is especially concerning for levees that are already stressed, such as those on Tyler Island, where major levee slumping is putting the Delta island at risk.
Our hearts go out to our friends who are fighting high water and reminding us of the importance of solid O&M and new capital projects, and the risks that we all face by living, working, or farming behind levees.