Thank you. The bottom of the spillway looks ready to break off.
That should cut down on the cost of demolition!
Realistically, the bottom will be torn out and replaced. The top will either be repaired or replaced. A good assessment can't really be done until the water is down enough that they don't need to use it for a while. Which also means getting the plant back on line.
Highway 41 road collapse near the entrance to Yosemite
http://www.freerepublic.com/focus/f-news/3527653/posts
Yup, it has been undermined.