Here is Saturday morning’s installment of our update on the Oroville Dam spillway incident and more news about the valley. In summary, Oroville’s Powerhouse is still not able to produce power; 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 now evacuating 70,000 cfs from the reservoir; but new storms have started to roll in.
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Here’s a recap of the last couple of days of activities surrounding the Oroville Dam spillway incident:
1. On Thursday, DWR reduced outflow from 100,000 cfs to 80,000 cfs from the primary spillway at Oroville Dam in order to remove debris from the diversion pool (which is the body of water into which the spillway dumps water). A key reason to remove debris from the diversion pool is for the eventual reoperation of Hyatt power plant, whose operation would be hindered by debris. The powerplant is an underground hydroelectric facility that should assist in releasing water from Lake Oroville once it restarts (it is capable of releasing up to 13,000 cfs). In further support of removing debris, DWR decreased the releases to 70,000 on Friday. DWR was doubtful, however, that the power plant could start up by early next week when heavier precipitation is predicted. While many people might question lowering releases just to support electric production, releases through the hydro facility is also how DWR provides irrigation releases during the summer once the lake level drops significantly. This graphic from public.tableau.com shows both the inflow (you can see just how massive that storm was last week) and outflow over the past week and a half (see upper graph). In particular, you can see DWR’s efforts to control and increase releases from the primary spillway despite the ongoing erosion. (Click here for a good article on possible causes of the erosion of the primary spillway.) The graphic also shows the lake level compared to the elevation of the emergency spillway (lower graph). (Click here for the original.)
2. DWR continues to reinforce sections of the emergency spillway whose sudden erosion led to last weekend’s evacuations. We learned on Friday that there are four priority sites for repair, and each is advancing well as follows: site 1 – 100% complete; site 2 – 50% complete; site 3 – 75% complete; and site 4 – 90% complete, all as of Friday afternoon. With 70,000 cfs of water being released, the reservoir had declined to just under 856 feet by midnight Friday.
3.Without a doubt in some watersheds this is now the wettest year on record. In the Yuba Watershed, the rainfall thus far this year is at 110% of the average ANNUAL rainfall, and we still have many months of weather to come. In fact, the inflow into New Bullards Bar Reservoir on the Yuba River this year is already more than the inflow in 2013, 2014, and 2015, combined. In the Yuba River watershed, there has already been 15 inches more rainfall than the wettest year on record.
4. Another set of storms arrived on Thursday and could produce heavy precipitation starting Monday. Between Friday and Sunday light to moderate precipitation is anticipated. Heavy precipitation will likely result in higher inflow into Lake Oroville, but the Weather Service has indicated that the anticipated rainfall is still much lower than what we saw last week when the principal spillway first suffered damage. In this graphic from the National Weather Service (click here for the original), you can see on the top graph the estimated rainfall for the next few days. Note that each bar is for a six hour period, so you need to add them together to see the estimated total rainfall in a day. The bottom graph shows the historic and estimated water surface elevations at Gridley. Note the significant drop off of water surface elevations for this weekend, likely because of projected decreased releases to work on the Hyatt Powerplant.
5. On Wednesday the Sutter Butte Flood Control Agency, which has constructed levee improvements over the last four years along the west side of the Feather River (downstream of Oroville Dam), authorized $5 million in immediate reinforcement measures just south of Yuba City. The measures, which focus on areas that have not yet been repaired as part of the agency’s larger project, are proactive in light of already high flows in the river and will bolster vulnerable parts of the levee in the event of a more significant release from Oroville Dam.
6. Elsewhere in the Central Valley flood control system, Tyler Island was able to finish reinforcement of the levee that had significantly slumped, thus ending the mandatory evacuation of the Island. North of the Delta, a number of districts continue to struggle with saturated levees which are significantly seeping or showing many boils.
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.
That’s it for today. Please check back as we continue to update you on how the system is doing.