Flood Terms

Last week there were a bunch of stories about how the tiny community of Gulfport, Illinois had been swallowed up by the Mississippi river and how many residents hadn’t bothered getting flood insurance:

Gulfport was protected by a levee rated to withstand a 100-year flood. Although it wasn't designed to protect the town from a flood on the scale of last week's, it was enough protection that the Federal Emergency Management Agency did not require business or homeowners to purchase flood insurance.

Only 28 of the town's 200 residents had federal flood insurance. The rest trusted that the levees would hold. Residents Rick and Gina Gerstel, who lost everything, say no one from their bank to the municipal or federal governments ever told them they were at risk and ought to buy flood insurance.

Gulfport sits right up against a bend in the Mississippi River across from Burlington, IA. Just looking at the map (and never having been there) it seems to me you might want to have flood insurance if you live that close to one of the great rivers of the world. Even if the government doesn’t require it.

(Also, why does Google maps call it Gulf Port, two words, when no one else does?)

As for the term 100 year flood, many think it’s time to retire it because it’s misleading:

The terms have practical consequences; they are used for such things as classifying a levee's protection level and setting insurance requirements for people who live in flood-prone areas.

Many people seem to believe that a 100-year flood should happen once every 100 years, or that a 500-year flood should happen every 500 years. But that's not how it works.

A 100-year flood is defined as a flood so big that it has a 1 percent chance of happening in any given year. A 500-year flood is one with a 0.2 percent chance of happening in a given year — a 1-in-500 chance.

Scientists say it is not unusual to hear from people who want to know if they have lived through a "100-year" event and want to cancel their flood insurance, believing one recent big flood lowers the risk of another. But that's not the case.

While the rules of probability say that the odds are 50-50 that a coin will come up heads, it is entirely possible to flip a quarter and come up with heads four or five times in a row.

Ah, the rules of probability. You just never know. Get the insurance.