Probably because developers, real estate agents, and current landowners often use terms like Garrison can prevent floods and the senators have whipped the Corps into shape so they won't allow flooding in the future. Anything it takes to soothe a prospective buyer. Truth is, nobody in their right mind would spend the kind of money required to "prevent" all future floods along the river.
I've never heard anyone at the Corps, much less any hydrologist I know of, tell someone that 2011 can't happen again. Nature's records are meant to be broken. We have less than 150 years of good data on the most studied of our rivers, that kind of pales in comparison to Mother Nature's longevity. There are some really interesting journal articles out there about paleo floods in the Black Hills that would scare the Shiite out of me if I lived anywhere near some of those streams and rivers. Flood deposits high on the side of a canyon are pretty good evidence that we ain't seen nothing yet.
I once also said dumb things to people around Devils Lake. Stuff like, so you came out here, took a walk around the land, and thought this was a great place to build when you could see driftwood sticking out of the hillside about 20 ft above your main floor, really?
Answer I usually got was "yeah, but that was different back then because of x, y, and z"
Hell, at one point in the not-so-distant geologic history there were sand dunes in ND. We now call that area the Sheyenne National Grasslands. So we absolutely know that there are things out there that will get us wet, and there are unknowns(?) out there that will one day turn the state back into a desert. Some of the glacial advances took place over around 200 years, if my memory serves me correctly.
Thankfully, we got to be the dominant life-form on planet Earth by being adaptable.
