I did go back to find when the Mississippi River flooded in the St. Louis area so they called it a 100 year flood. Going back as far as I could find data - it happens more frequently than you would think. In fact on an average of every 8 years we have (what is called) a 100 year flood. So it is relatively normal for this to occur. Once we had what the press referred to as a 100 year event twice in three years. And three times the water got to within 2 feet if the top of the levy's. When I first got here the old timers then - talked about where the water flooded before they built the levy's. If they had not built those levy's I might be living on the bluffs a few miles further east. It was the frequency I experienced and the talk of those old timers that got me looking into the data. So I think that the "100 year" label has gotten to be a media thing and not rooted in actual history.