There were no ordinances against building in flood plains when the French founded New Orleans.
I did not think there was. I know one factor that will be very prominent in any rebuilding of New Orleans is the insurance industry. A lot of the big name companies are pulling out of Florida. Oh they'll still take our money for auto insurance and they will still insure commercial interests but joe and jane homeowner are tough out of luck.
I bet you will see the same thing in LA, Al and MS. The insurance companies will push for stricter codes. Without stricter codes insurance companies may just pull out of the region. Since most mortgage companies will not make loans on uninsured property you can imagine what the lack of available insurance would do to any rebuilding effort.