That's certainly a claim worth examining. To us, that would mean that the dam would have to be the size of Hoover Dam, or have supernatural properties. Lets see how well the dam does in protecting homes from floods, which is what it is supposed to do. It's clear that the non-structural alternative provides more widespread protection. Lets look at the numbers with that in mind.
Lets see how many homes are actually protected by each alternative.
This is the flood that each alternative provide protection. That translates to 143 more homes damaged if the dam is built rather than the non-structural alternative. And doing both doesn't do much more. With Dark Hollow Dam, fifty-six more homes suffer first floor damage. And adding the dam doesn't add much protection.