There are several issues at play that I think y'all might be interested in exploring.

1. New Orleans was founded in the early 1700's on the first major high ground upstream from the mouth of the Mississippi River.

2. Some parts of the city have not flooded in recorded history.

3. The French settlers were mostly poor and from cities in France. They were led by military aristocrats of minor French nobility. None of the settlers knew squat about farming in a subtropical delta. What they did know of farming was from temperate French methods and French crops and French livestock which were almost completely unsuitable to the region.

4. The 2nd and 3rd wave of French settlers were plantation farmers who knew how to work slaves to grow sugarcane and cotton. They hired overseers from French colonies in the Caribbean and brought in slaves from those colonies, principally Haiti but also Martinique and some from French West Africa.

5. The French attitude towards slaves was quite different from the Anglo-German attitude. The French legally recognized the products of liaisons between owners and slaves, for example. Also, manumission of faithful slaves was not uncommon. Slave families were almost never broken-up and sold. Slaves were often asked about potential sale to another master or would ask to be sold to another master. House slaves were often educated. Occasionally well beyond reading and writing. With the owner's permission, slaves could own property and even have a business.

6. Plantation owners farmed the low ground around NOLA. They built canals to help drain the low ground so they could plant earlier in the season. Slave quarters for field hands were built near the fields. Annual floods often washed-out the slave quarters and flooded the fields so the plantation owners built low levees, less than 3 ft high, around their fields.

7. The population grew and expanded into the leveed agricultural areas. Levees were raised to increase flood protection in the late 1700's after a couple of especially severe floods and a major yellow fever epidemic.

8. Trade up the Mississippi River and overland to the Natchez Trace expanded dramatically with the expansion of the plantation system up the Mississippi and Red Rivers.

9. The population of NOLA began to grow exponentially from "Americans" westward expansion and immigrants from France and later, Spain (France sold Louisiana to Spain). The levee system was expanded and raised.

Unbeknownst to geologists of the day, leveeing and drying the relatively unconsolidated soil surrounding NOLA increased oxidation of the highly organic soil resulting in compaction and subsequent loss of elevation. Also unknown to geologist was the fact of deltaic subsidence due to dewatering and overburden compression. Finally, nobody knew that leveeing, which held the river floodwaters out of the city, would prevent resaturation of the soil (preventing or slowing oxidation) and fertilize the vegetation which actually "grows" land.

Continue the above for another 150 years of plantation farming, increase levee expanse and height, and channelizing all of the upstream tributaries to increase run-off and drain wetlands up into the Ohio, Tennessee, and Missouri Rivers systems and we have the city of New Orleans.

B