Thanks for that article, Robert.
For those discussing New Orleans, I'd like to provide some data. First, much of New Orleans - particularly the heavily populated areas (pre-Katrina) do not tend to be below sea level. Below is an elevation map of the city where yellow areas are 5 or more feet below sea level and grey areas are more than 10 feet above sea level. White areas are at or near sea level. Notice that the areas near the river and downtown (including the French Quarter near the top right of the horseshoe curve of the river) are all above sea level. Only those areas near Lake Pontchartrain to the north are 5 or more feet below sea level. These areas were primarily swampland and not heavily populated until after construction of the flood control canals that were protected by levees (three short canals in Orleans Parish near the center of the map). Two of these levees were breached during Katrina (blue circles on the leftmost and rightmost flood control canals.
The Port of New Orleans is the fifth busiest port in the US. It's easy to say that New Orleans should be abandoned, but the fact remains the the mouth of the Mississippi River is the only navigable route to transport cargo from the southern end of the country to the northern end as well as connections through other rivers to points east and west. Commercial interests alone make the suggestion of abandoning New Orleans ludicrous. The Port of New Orleans combined with the Port of South Louisiana in suburban LaPlace form the largest port system in the world by bulk tonnage, and the world's fourth largest by annual volume handled. It is these same commercial interests who wanted to boost capacity by constructing an industrial canal that would allow for a shorter route for commercial cargo through the city to Lake Pontchartrain rather than around it. Construction of the Industrial Canal (officially called the Inner Harbor Navigation Canal) was completed in 1923. The levee system has been periodically shored up -- usually after a flood event and levee failure -- including a major project that was approved after significant flooding occurred with Hurricane Betsy in 1965.
Please note the narrow southern end of the Industrial Canal near where it meets the Mississippi River. The area just to the right (east) of the Industrial Canal near the river is the lower ninth ward. As you can see this ward is not below sea level and was flooded by the levee breach along the Industrial Canal just to it's north (blue circle on right side of the canal near the "Y"). The upper and lower ninth ward were destroyed by the extreme volume and sheer force of the water coming through the breach (think of the force of a lake trying to squeeze through what proportionally amounts to the diameter of a fire hose).
Most of the people of the lower ninth ward did not have flood insurance; not because they were poor, but because they were not in the FEMA flood zone map and were encouraged NOT to purchase flood insurance. Below is a link to the FEMA flood zone map for New Orleans (pdf). Anyone in a white area was told they didn't need flood insurance. The "dots" overlaid on the map indicate post-Katrina inspections. The FEMA zone is indicated by the color of the background on the map. The FEMA map for the lower ninth ward is primarily white. Yes, the people of the lower ninth ward were generally poor. Yes, they tended to be black. No, they have not come back in large numbers but it's primarily due to the fact that, of all of the neighborhoods in New Orleans, theirs is one of the few that FEMA determined was not a flood zone. Without flood insurance they have no resources to rebuild.
There has also been some discussion here about the level of the re-population of New Orleans. Using mail delivery addresses as an indicator, there were 72% of the mail delivery addresses receiving mail in June 2008 (146,174) compared to June 2005 (203,457). Below is a link to an interactive re-population map that allows for block-by-block comparisons of pre- and post-Katrina occupation. As you will see, the lower ninth ward is not exactly "depopulated" but it's numbers remain small in comparison to the rest of the city.
I agree with the statements in the article Robert linked above. Areas such as the swamplands near Lake Pontchartrain that are lands not naturally habitable allow for greater population centers and greater loss of life and property in a natural disaster. On the other hand, areas that are naturally habitable become inhabitable due to human interference such as the building of insufficient levees (keep in mind the Industrial Canal and it's levees are not to protect against natural disasters, they are intended to maximize commercial shipping through the city) and the destruction of the natural barriers - which is also primarily due to human interference but I'll tackle that one another time.