Given the amount of erosion what are your thoughts regarding the feasibility of the spillway remaining at this location?
First of all, a new engineering team versed in correcting dam issues has to be brought it with some reliance on a forensic team looking at the original issues and investigating what happened.
After the new team comes up with some A, B, C approaches that same forensic team needs to do an internal Peer Review for the new team to avoid not having looked enough at choices.
The spillway gates are performing well it appears and duplication them adds six months of work to an already too tight schedule. Add another spillway later in a manner that does not involve the main dam if you must, but put this thing properly back in service with features revised to avoid failures.