GeoCarta Has Moved

Sep 5, 2005

New Orleans Flood Map

In a previous post I mentioned the Flood Insurance Rate Maps prepared by the Federal Emergency Management Agency (FEMA). So the question arose, "what do the flood maps show for New Orleans?" So I got on FEMA's website and made a map of a portion of the city. The title block is at the upper right.

In the lower right, is a small section of the flood map. The shaded areas indicate land that lies in the 100 Year Flood Plain. Considering the news reports, it comes as no surprise that nearly the entire city is located in the flood plain. The two white fingers you see at the bottom of the map are the tops of levees. I hope it is legible, but below the label, "Zone A0" is the the statement, "Depth 1.5" This would indicate that the flood waters would reach a depth of 1.5 feet. While I am no hydrologist, it is clear that this flood map only contemplates the flooding that will occur from rain fall. When a 100 year rain comes, the water will naturally flow towards the river, lake and canals. The levees around these bodies of waters block this storm water and cause localized flooding. However, the flood maps clearly do not contemplate the castastrophic failure of the levees. This is true of any area of the country protected by levees, the flood study assumes the flood structures will function as designed. However, I can't help but wonder if these maps did not contribute to a false sense of security among New Orleans' residents and government officials. 1.5 feet of flood water does not pose nearly as great a potential for lose of life as 20 feet. Perhaps FEMA should take a look at this issue and consider modifying their maps in areas protected by man-made structures.

I posted a full-size version of the flood map here. Be warned, its 5.1 mb in size.