What is a “100-year flood event”?
A “100-year flood event” is a fairly large, historically-infrequent flood. To be precise, it is a flood of a size that is projected to have only a one-percent (one in 100) chance of being equaled or exceeded each year. This does not mean that this size of flood will only occur once every 100 years. The likelihood of a 100-year flood occurring within a 100-year stretch of time is very high, but there is no way to predict when the next flood will occur – or the one after that. We could have several 100-year floods in a short period of time, or we might not see a 100-year flood in our lifetimes or our grandchildren’s lifetimes.
