More rain coming Wednesday, for several days. Supposed to be as big of a rain event as the one that caused this - by raising lake level 20 ft. Only now it is full, and they had to shut down part of the power plant, so even more flow headed towards the spillway. The lower 2/3 of the main spillway is basically destroyed. They are reluctant to put high flows down that because it is eroding towards the damn. This is a compressed earth damn, not a concrete gravity arch like Glen Canyon or Hoover. So they are using the emergency/ auxiliary spillway (for the first time). The concern there is, dumping water over that low wall may (almost certainly will) damage it’s foundation. Can they dump enough without too much damage? If the low wall that forms the auxiliary spillway failed, they uncontrollably dump the top 15 or 20 ft of the lake - causing flooding downstream. My guess is, they will run what they can through the power plant. Dump as much as they can get away with through the main spillway without letting it erode too much further towards the damn. Then the rest goes over the wall and erodes the heck out of that hillside. If that wall has to fail, so be it, they will sacrifice that to save the dam and prevent an even larger disaster.
Correct me if I’m wrong but the main spillway appears to be located on natural topography, it’s a hillside not the manmade earthen dam. Looks to me as if the likelihood of catastrophic failure is far less with the main spillway than with the emergency spillway, which does pose a risk to the manmade earthen dam. Worst case with failure of the main spillway is the 30 ft of water off the top of the reservoir being cut loose down the side of that hill, not a good scenario but far better than the dam itself failing.
The power pant can only handle something like 10-12k cubic feet per second. The earthen dam core isn’t under threat. The spillway and the auxiliary spill area appear to be separated from the main body by significant bedrock.
This is the kind of problem we (Americans) used to kick ass on. If I had to manage this I’d take the current dry break and rip-rap and fast set shotcrete the hell out of both areas, even going so far as to lay a temporary rail spur in there to get in material. That would probably enable it to make it through successive storms, repeating after each until you got a long enough break
That you could rough form the spillway to receive backfill in the form of controlled density fill followed by forming the actual spillway up and casting it with a reinforced concrete that would attain at least 3500+ psi compressive strength in 5-7 days.
Realize though that their is a host of clowns whose bread and butter are going to come from thinking this to death, and feeing and studying the shit out of it, plus with that kind of water possibly offline the politicians get to keep riding the summer water restriction gravy train.
I confess that I am surprised that a dam that big is a dirt banked structure. I am not an engineer,but for a mass of water such as Oroville lake I would think a concrete dam would be required.