So What Does The "100 Year Flood" Term Mean...

Each spring, as the shores of the Ohio River widen due to flooding, we hear the term "100 year flood" tossed around in the media and beyond. This term is used without explanation and is often misunderstood. Many folks labor under the belief that such refers to a catastrophic flood occurring once every one hundred years. Nice thought---but not accurate.

What the "100 year flood" term means is that there exists a 1% chance that the River will reach such level each year. That's right, we could have a "100 year flood" two years in a row without the term being inaccurate. The point is that there exists the same 1% chance of the river hitting the "100 year flood" level each year.

Another issue to point out regarding the "100 year flood level" term is that the National Weather Service has calculated such figure utilizing only  a century (or so) of data. As such, what is the "100 year flood level" today may well be different in the future as more data becomes available.

Just thought you would want to know.....