Actually, I believe it was done from about 1500 miles away.
(by an engineer intimately familiar with the short-comings of the original design)
Sounds like this “engineer” is well respected (i.e. to be 1500 miles away & “sought out this advice”).
Engineers have stated that the large MS concrete crest structure & sluice gate is anchored in bedrock. This seems to infer that the “vulnerability” is to protect the sub structure of the main spillway (slabs & sidewall system).