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Rolling the dice on local home flooding

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Why Do We Let Washington Play Vegas Bookmaker on Flooding?

If you go into any sports book in Las Vegas to bet on an upcoming game, you’ll find various odds and points spreads based on which team is believed to have a better chance of winning.

While there are many different sports books and bookmakers, they tend to cluster around similar betting lines and odds, giving gamblers the ability to measure risk and place bets in an atmosphere of relative stability.

For decades now, our federal government has been in charge of its own form of bookmaking — setting odds at the American Flooding Casino.

  • NOAA — the National Oceanic and Atmospheric Administration — is responsible for gathering and analyzing historic rainfall and determining the probability of intense storms taking place in particular locations. These “Point Precipitation Frequency Estimates” are published in a document known as Atlas 14. When people talk about a “100-Year Storm,” that’s the amount of rain NOAA estimates would fall in a storm that has a 1-in-100 (or 1%) probability of happening in a one-year period.
  • FEMA — the Federal Emergency Management Agency — takes these estimates of extreme rainfall, models where water goes in a flood and draws maps that estimate the odds of a location being flooded in any given year. This “100-Year Floodplain” is the area that FEMA estimates will flood in a 1-in-100-years event.
  • Those estimates aren’t just numbers in a table and lines on a map — they have huge real-world impacts:
    • FEMA’s maps are used to determine who is and isn’t required to buy flood insurance in order to have a federally backed mortgage; cities often use the 100-Year Floodplain as a marker of where it is and isn’t safe to build; homeowners decide whether to insure against flooding based on whether they are in the floodplain.
    • Stormwater engineers use NOAA’s numbers to build systems for handling rainwater and runoff; in many municipalities, the literal size of the stormwater pipes that a city lays in the ground is determined by whether they are able to carry the amount of water that NOAA says will fall in a storm estimated to occur every 5 years.


But what happens when the numbers in the NOAA atlas and the lines on the FEMA map bear no relation to reality? 

Take Horry County, for example …

In October 2015, a massive storm system fed by moisture from Hurricane Joaquin dropped 14.73 inches of rain into the Waccamaw River just above Conway over a four-day period. According to Atlas 14, that amount of rain should fall roughly once every 200 years in Conway.

One year later, on October 7-8, 2016, Hurricane Matthew brought 11.31 inches of rain to the Waccamaw over two days. That’s a once-a-century amount of rainfall in Conway — again, according to NOAA.

And in September 2018, 15.44 inches of rain fell over three days during Hurricane Florence. NOAA’s atlas says that’s a once-in-500 years rainfall in Conway.

According to the odds set by the federal government, three storms of this intensity ought to occur within three years of one another at this location approximately once every 408,043 years. (Just for context, the entirety of recorded human history totals 5,000 years.)

Gamblers would call that a “bad beat” — which is less funny when you consider that thousands of Horry County residents were flooded multiple times in those events, making the county one of the nation’s leaders in flood insurance claims and costs.

And it’s not just Horry County. Across the eastern United States, the New Normal has become extreme rain events and flooding that according to the U.S. government are extremely unlikely to happen in any given year.

This isn’t “unluckiness” or “a bad streak.” This is our federal government completely missing the boat on flood risk.

If you were a sports gambler, would you continue placing bets with a bookmaker who consistently set wildly off-the-mark odds? Then why do we continue to treat the federal standards as though they’re some sort of truth?

If 2015-2018 is a New Normal, then all bets are off in Horry County:

  • Huge sections of our county — a low-lying coastal plain that sits at the bottom of the Pee Dee Watershed — are served by flood control infrastructure built to serve agricultural purposes in the middle years of the last century.
  • The flood infrastructure we’re building today assumes the federal government knows what it’s doing — and that the storms of recent years were just an anomaly.
  • And we haven’t even begun building the flood infrastructure needed to protect the 275,000 new residents county leaders tells us are on their way over the next 20 years.

If we’re going to get repetitively flooded families out of harm’s way and keep all the new residents dry in the New Normal, we must stop debating the definition of the 100-year floodplain and take an aggressive approach to building infrastructure that can convey and store massive amounts of stormwater.

Groups like Horry County Rising — a diverse, grass-roots group of citizens working for a sustainable future — are taking these questions directly to elected officials and holding government accountable for reducing citizen vulnerability. To learn more, check out our Facebook page and join our movement.



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