1. All of the remaining spillway is damaged or undermined beyond repair. There is just too much bad construction and damage to be sure that a patch job will not fail in the future.
2. I am very concerned about the main spillway gate structure. There is some limited information that it is weeping more than expected or designed to.
3. The e spill is a joke and needs to be seriously evaluated and dealt with.
I think the prudent course of action is the construct a new spillway - including a gate structure - adjacent to the existing one using modern techniques and design. This would allow the project to go through another wet cycle using the damaged system, in the meantime, if needed. Caisson pier system and pressure grouting the “bedrock” down to a 100 feet of so would stabilize the area significantly. Modern rebar specifications and concrete technology. They are not going to catch any breaks on this situation. The geology and past sins are an too big of a hill to climb
That thought keeps running through my head.