Rain, Storm Surge Combine to Put U.S. Coasts at Risk

After the devastation of Hurricane Katrina, New Orleanians thought they knew what areas were susceptible to flooding during a storm.  So when Hurricane Isaac, a much weaker storm than Katrina, bore down on the city in 2012, those who live to the west of Lake Pontchartrain weren’t worried, as they had been spared the raging waters that inundated so much of the city during Katrina.

But Isaac turned out to be the perfect storm for that area.  The surge that Isaac pushed ahead of it raised lake levels by 6 to 9 feet, and they stayed elevated for an unusually long time.  At the same time, the area around the lake saw 11 or more inches of rain from the storm. Because the lake levels were so high, there was nowhere for the rainwater to drain, and so water flooded the streets and houses to the west of the lake.

“Many people were caught off guard,” Hal Needham, a storm surge scientist at Louisiana State University said, and thousands had to be rescued from the rising waters.  It turns out that many more coastal residents are at threat from the meteorological double whammy of freshwater flooding and storm surge, which a new study finds is a serious threat for large stretches of U.S. coast.

That one-two punch – called compound flooding -- isn’t something that many places in the U.S. plan for, however, as studies of risk tend to look at one danger or the other, Needham said. And global warming-driven sea level rise exacerbates the problem even further.

Read more at Rain, Storm Surge Combine to Put U.S. Coasts at Risk