And yet there were considerable works and plans in place to prevent exactly that from happening. Almost like people aren't completely retarded about where they lived and considered such a possibility.

Much like this, it was slowly chipped away through years of corruption, incompetence, and disregard. If everything was at correct preparation, most of the city would have been spared considerable damage.

Also New Orleans was 100% above sea level when it was built. A century+ of pumping water out caused the land to dry out and sink to below sea level over the course of the 1900s. And its still only about half of it that's below still.