A 100-year flood is the flooding elevation that has a one percent chance of happening each year. Why is the name misleading

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Jamie Webster

Physics

14 July, 00:45

A 100-year flood is the flooding elevation that has a one percent chance of happening each year. Why is the name misleading

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Adison Webb · Answer 1

One percent annual chance of flooding does not mean it will happen with absolute certainty once every 100 years. Just that the expected value of a flood in 100 years is one.

As an example, heads has a 50% chance of happening every coin flip. With 2 coin flips, the expected value is one. However, it would be a misnomer to call "heads" a 2-flip outcome.