This tell's you why the flooding was so bad where it was. The dark red
areas are where the land is at it's lowest, which is by the lake and in
East New Orleans. The green areas are natural levees, built up from
eons of Mississippi River flooding before there were even settlers in
the New Orleans area.
The cross section is represented by the heavy dashed line in the
picture above. This helps explain why the French Quarter mostly escaped
flooding.
New Orleans Elevation Map