Misconceptions of the 100-year Flood

  The recent flooding of Indian Creek that led to the damage and closing of Coach’s Bar and Grill has brought much attention from local papers and news stations. Several local media outlets have presented the flood as a “100 year flood event.” But what makes a flood a “100 year flood”? Due to the nomenclature of the 100-year flood, many are often confused as to the likelihood of such an event happening, and, as a consequence, may under prepare or under insure with the illusion that a flood of this magnitude is a once-in-a-lifetime event. A 100-year flood event should statistically happen once every 100 years over a long time period, or have just a 1 percent chance of occurring within any given year. When people hear that a 100-year flood has occurred on a particular river, they may incorrectly assume that a flood of that magnitude should not happen again for roughly another 100 years. This is the same logical fallacy that would lead one to believe that flipping a coin and it coming up heads four times in a row is far more unlikely that flipping alternating heads and tails four times (statistically speaking, each are equally likely). Probabilities of this time scale should only be applied over long time horizons and cannot be accurately applied to short time periods. Therefore, back-to-back rare events may be more common than one would originally believe. In addition to misinterpreting the definition a 100-year flood, there are a few other issues that can lead to error in attempting to predict such an event. First, there is a common misconception...