Breached levees: flooding extends beyond mandatory flood insurance zone

By David Jacobson, Temblor

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Yesterday we highlighted the strengths and weaknesses of the FEMA flood mapping program using the ongoing flooding in the Midwest. Because flooding has continued, caused loss of life and disruption, and in some cases gotten much worse, we thought we’d take a closer look at the areas hit hardest, how flooding has impacted the region, and the importance of flood protection.

Due to heavy rainfall that began over the weekend and will continue through today, record flooding has been observed at 14 locations across Missouri and Arkansas. Some of these records had been held for over 100 years showcasing the magnitude of these floods. In the figure below from the National Oceanic and Atmospheric Administration (NOAA), rainfall over the last week is displayed. While heavy rainfall alone resulted in flooding across four states, matters were compounded when levees started failing, leading to inundation in areas outside of flood zones.

 

One of the areas hit hardest by levee failure is the town of Pocahontas, Arkansas. Yesterday morning, flood waters from the Black River overtopped levees, causing them to fail, and leading to flash floods and the evacuation of 6,500 residents. The first image in this blog post shows one of the breached levees near Pocahontas, which has caused significant flooding to the east of the Black River. In the image below, from Ryan Vaughan of the Region 8 Storm Team, the scale of the flooding can be clearly seen. For comparison, the FEMA flood map of the area is also shown below.

 

 

What is evident from the image comparison above is that due to levees breaching, a much larger area flooded, including significant regions not marked by FEMA’s flood maps, and thus outside the mandatory flood insurance zone (10% chance per decade zones). While this is understandable, since FEMA would have based their maps on levees holding, it does bring up an important point, are people protected from flooding by levees aware of the hazard? If they are not, they should be informed since many levees protecting towns in the Midwest and the rest of the country are old and not capable of surviving should they be overtopped. It also begs the question, should people that are protected from by levees still carry flood insurance? Regardless of what the correct answer is, being aware of what your protection from inundation is is an important matter in areas prone to flooding.

 

References
FEMA
NOAA
The Weather Channel
The Washington Post
Weather Underground

 

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All other inquiries, click here