A lot of what happens initially depends on the position of the wicket gates. Prior to complete failure I believe erosion around the ends would start to destabilize the damn itself. Eventually it would end up as a huge rock in the middle or side of the river.
Great stuff Dave. You know I would buy all this, but finally you have found duplicate in my collection. GLS. For any potential buyer, Dave is a straight up honest seller.
If you want to strengthen you all of your legs I would suggest listening to Ben Patrick on this podcast. You can also find him on youtube as knees over toes guy. His story and accomplishments are incredible.