Bowling Green’s 1000 Year Flood Numbers

Over the weekend, many of you saw the flooding and resulting devastation across South Carolina from the incredible amount of rainfall they had. A trough of low pressure dug deep into the southeastern US, and caught a stream of higher moisture values off of Hurricane Joaquin.

This trained over the same areas for hours, and several days, leading to a ridiculous flooding event down there.

A lot of these areas can be described as having a “1000 year rainfall event”. But what does that even mean? Well, a 1000 year rainfall event is basically just describing an amount of rain falling over a set timespan that statistically would only have a .1% chance of occurring each year. As the name implies, they are fairly rare.

So, what does this look like for Bowling Green? What would a 1000 year rainfall look like? Or what would a 500 year rainfall look like, etc? Luckily, I have the numbers here! This chart is a bit complicated, but I will explain it here in a sec.

h/t http://hdsc.nws.noaa.gov/
h/t http://hdsc.nws.noaa.gov/

There are two separate graphs here. The top graph is showing us the relationship between the duration of he event, and the event in inches. The curves are representing the recurrence of the event itself in years. The bottom graph is showing us the relationship between the interval of recurrence, and the amount in inches. The curves are showing us the duration of the individual events.

So, in a simpler manner, here are some of the more useful data I found:

A simpler visual for the 1 hour rainfall intervals. h/t http://hdsc.nws.noaa.gov/
A simpler visual for the 1 hour rainfall intervals. h/t http://hdsc.nws.noaa.gov/
  • 1 hour rainfall intervals and totals:
    • 1 year: 1.27″
    • 10 year: 2.11″
    • 100 year: 3.00″
    • 500 year: 3.66″
    • 1000 year: 3.96″

 

A simpler visual associated with the two day rainfall intervals. h/t http://hdsc.nws.noaa.gov/
A simpler visual for the two day rainfall intervals. h/t http://hdsc.nws.noaa.gov/
  • Two Day rainfall intervals and totals:
    • 1 year: 3.55″
    • 10 year: 5.98″
    • 100 year: 9.06″
    • 500 year: 11.7″
    • 1000 year: 12.9″

 

A simpler visual for the 7 day rainfall intervals. h/t http://hdsc.nws.noaa.gov/
A simpler visual for the 7 day rainfall intervals. h/t http://hdsc.nws.noaa.gov/
  • Seven Day rainfall intervals and totals:
    • 1 year: 4.76″
    • 10 year: 7.97″
    • 100 year: 11.9″
    • 500 year: 15.2″
    • 1000 year: 16.8″

 

What I find interesting is that there were areas in South Carolina that eclipsed their Three Day Total Rainfall, 1000 year flood estimates by up to 4″. That is just ridiculous.

Analyzing this locally, we need obviously are going to point to the May 2010 flooding, and compare those numbers to these. We know that much of Tennessee saw a 1000 year flooding event during that, but what about here?

h/t NWS Louisville
h/t NWS Nashville
h/t NWS Louisville
h/t NWS Louisville

While that flood was absurdly bad in the region, the interval of occurrence was on par with a 100 to 200 year flood. To find a 1000 year flooding event, you would have to go back to January of 1937 when 20″ of rain fell in about a 12 day timespan, which is approaching the total for the 20 day, 1000 year flood.

So, next time it rains, think about whether or not it could be a 1000 year flood. Odds are, it won’t be. If you wanna have some fun and figure out other places stats like these, just click on this link and select the town!