Ask the editor: What is a 100-year flood?


The New Braunfels edition of Community Impact Newspaper recently explored ongoing flood initiatives in the city. Often, flooding events are referred to as 50- or 100-year floods. What does that mean?

Importantly, the terms do not mean that it is a flood that will happen every 50 or 100 years. Instead it refers to the likelihood that a flood will happen.

So a 50-year flood has a 2 percent chance of happening in any given year, and a 100-year flood is a flood that has a 1 percent chance of happening in any given year.

For reference, officials have estimated that the Memorial Day floods of 2015 were nearly a 200-year flood—an event with a 0.5 percent chance of occurring in a given year.

These calculations are important, particularly when it comes to neighborhoods that are located in flood plains. For example, if a neighborhood sits in a 25-year flood plain, that means it has a 4 percent chance of flooding in any given year.

Share this story

Leave A Reply

Rachel Nelson
Rachel Nelson is editor of the New Braunfels edition of Community Impact Newspaper. She covers local business, new development, city and county government, health care, education and transportation. Rachel relocated to Central Texas from Amarillo in 2009 and is a graduate of Texas State University's School of Journalism and Mass Communication.
Back to top