The water/debris in the power house is a direct result of the tailwater (bottom of the dam) rising up a great deal during the initial spilling. They scoured out a LOT of earth on that run, especially when they ran at 100,000 cfs in panic-mode (reality-induced panic, I might add). I don’t remember how high the tailwater rose, but it dropped 25 feet or more within a few hours of shutting off the spillway the first time.
There’s a lot there that needs attention, if not fixing. The most obvious issue right now is the main spillway. For now.
That seems like a design and an operational fault. Apparently there is no gate or valve to prevent tailwater entering the powerhouse, which is a design issue. Once the situation was developing nothing was timely deployed to prevent tailwater entering the powerhouse, which is an operational issue.
There seems to be a culture of complacency.
After seeing the issues with the dam itself, maybe they need to first lower the reservoir water level to 660ft so at some point sooner than later they can begin corrective action there as well.
A lot of stuff.