A floodplain is any area that can be expected to flood occasionally. It is the lowland area adjacent to a ditch, river, creek, stream, or lake. With very few exceptions, almost all areas of the United States are subject to some kind of flooding when the right set of circumstances occurs. However, the risk of flooding varies from place to place.
Floodplain areas are often tempting sites for homes and businesses because of their beautiful views and convenient access to water recreation. Unfortunately, many lives are lost and millions of dollars in property damage results when people build in floodplains.
The reality is that if you decide to live in a floodplain, you will get flooded at some point. And, although the responsibility for establishing floodplain management programs lies primarily with local governments, you are an important part in making the program effective.
The first rule of thumb is to stay out of the floodplain; let the streams and rivers do what Mother Nature intended for them to do — transport excess rainwater runoff. The second rule is to learn about the flood hazards in your area (for more information, visit www.fema.gov or www.floodplain.org). If you do live in a floodplain, you need to learn what you can do to limit your flood losses. And, even if you don’t live in an identified floodplain, you may still suffer flood damage. Be prepared!
There’s no way to predict when the next flood will come or how big it will be, but past flooding gives some clues as to what to expect. Flood frequencies are determined by the chance of occurrence in a given 12 month period. You may have heard the term “100-year flood” or base flood. This is the nationally accepted standard that is used to designate regulatory floodplains.
However, a 100-year flood is not one that happens every 100 years. Instead, it is a flood so large it has only a one percent chance of occurring in any given 12-month period. You could go an entire lifetime and never experience a 100-year flood. Or, you could experience several in one year or within a few years.
The chance of a flood of a certain size occurring and then the same or bigger flood happening right away is like flipping a coin. Just because heads comes up first doesn’t mean the next flip will be tails. Each time the coin is flipped there is a 50-50 chance for either heads or tails. In the same way, when a flood has passed, the chances are reset. A 100-year flood has a one percent chance of occurring in one year. And, as soon as it happens, the chances are still one percent that it will occur again in the next 365 days.