Every component of the complex has issues.
The spillways have design/construction issues. The main spillway has operational/maintenance issues.
The dam has operational/maintenance issues at the wet area.
How did water/debris enter the powerhouse? Is there a design deficiency? Or an operational problem?
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.