Well, let’s run some numbers:
From Wikipedia, Lake Oroville catchment basin = 3950 sq. miles, or, 2,528,000 acres.
10” of (forecast) rain over that area is 2,106,666 acre-feet of water.
If 1/2 makes it to the lake by next Tuesday, that’s 1,053,333 acre-feet added to the lake.
Capacity of the lake is said to be 3,537,577 acre feet.
How far will it be down by Tuesday?
I’ll conservatively assume 8 days discharge at 85,0000,000 cfs drain rate, and adjust by -10,000 cfs for average continued inflow, which equals roughly 1.72 acre ft / sec for 8 days, or, 1.72 x 8 x 24 x 60 x 60 = 1,118,864 acre feet drained in 8 days. I suspect the real number will be better, by the time the new water really gets going, however, my inflow # is just a guess, as I really don’t have a good source of that information.
OTOH, multiple sources (LA Times, etc.) say the DWS is shooting for 1 million acre-feet reserve capacity, which is a little under my estimate, and seemingly dangerously close to my projected inflow. Plus, as best as I can tell from published graphs, Lake Oroville dropped roughly 100,000 acre-feet per day the 1st 3 days after the peak level was hit. Again, that is poorer than my estimate, and would come in well under 1 million acre-feet reserve capacity even if maintained, which I suspect it is not.
Recall that last week, DWS thought they could squeak by, but then the rains persisted longer than expected, AND, DWS shut down the main spillway when the major damage became apparent, after having already reduced discharge to buy time for the salmon at the Feather River Hatchery.
It could be close, early next week, esp. if this next system melts a lot of snow.
Looking at it another way, the system last week dumped 20” of rain, swamping, but not drastically so, the roughly 700,000 acre-feet reserve capacity available when the “big water” began to arrive. This next storm is expected to bring 10” of rain, again leading to an expectation of squeaking by.
It seems like dicey stuff, to me. If MO Nature throws CA a curveball, with either peak inflow rates of ~190,000 cfs (as with last week’s storm) or if the storm system unexpectedly stalls, at least that emergency spillway will fail.
In that case, if the bedrock below the emergency spillway is poor, the new channel may cut more downward than over to the main spillway and then the side of the dam. There will still be serious flooding downstream, of course.
If that bedrock is “good”, then lateral growth of the failure will approach the dam. My guess is that this might take a few days, and by then the “pressure” will be off of the lake. But, at that point, such serious damage will have been done that repair or mitigation is probably a futile attempt, until summer arrives. In fact, in this case, I would almost think that deliberate blasting of a deep channel through the emergency spillway would be the best bet, so as to save the dam itself while allowing a few months of moderate floods downstream, rather than have a final catastrophic “surge” sent downstream by a main dam failure.
Any way you look at it, if this next storm causes inflows like last week’s storm, it’s a big dam problem.
Thank you for your perspective.
Another problem is that parts of some roads are beginning to get washed out. IF they have to evacuate again that will be a real nightmare.
I do not disagree with any of your calculations. The Feather River starts in the Sierra Nevada & comes a long way with lots of watershed before it gets to Oroville Dam.
IF there is serious flooding, it will last more than ‘a few months’ & the entire rice crop & thousands of acres of alfalfa will be wiped out. The farms & ranches in the Sacramento Valley are BELOW sea level, depending on the levees to keep they dry. Dairy farms, horse operations, and other crops grown. The face horse California Chrome came from Yuba City area.
IF anyone here remembers the 1986 & 1996 floods into Marysville & Yuba City, they were pretty damaging—and the high water mark on buildings in Yuba City were over 10 feet above he ground. I saw that for myself, when I lived just east of Yuba City in Grass Valley.