Question

Which of the following is true of a 100-year flood?

1) An 100-year flood occurs every 100 years on a given stream
2) The probability of a 100-year flood occurring on any given year is 1:100
3) A 100-year flood cannot occur twice within 10 years
4) The probability of a 100-year flood is related to how recently the last 100-year flood occurred

Answer 1

A 100-year flood has a statistical probability of 1:100 of occurring in any given year. This means there is a one percent chance each year for such an event, and it is not prevented by the occurrence of a previous flood of similar magnitude.

Step-by-step explanation:

The term “100-year flood” is a term used to describe the statistical probability of a flood event occurring in a particular area. The correct answer to what is true of a 100-year flood is that the probability of a 100-year flood occurring on any given year is 1:100. This statistical figure does mean that a flood of that magnitude has a one percent chance of occurring in any single year; it does not mean that it can only happen once every 100 years, nor that it's related to how recently the last such flood occurred.

A common misconception is that a 100-year flood occurs every 100 years, but in reality, it is entirely possible for multiple 100-year floods to occur in a short timespan. This definition of the 100-year flood helps in understanding and managing flood risks, particularly in the development of floodplains and for creating insurance and flood prevention strategies.