#15: The Gradual Physical Sinking of New Orleans
A porch step can remain level while the entire neighborhood slowly loses elevation. New Orleans rests on young delta sediments containing water, clay, sand, and organic material that compress over time. Drainage made low wetlands suitable for construction, but drying organic soils and pumping groundwater encouraged additional subsidence in some districts. Levees protect the city from river flooding while also preventing fresh sediment from spreading naturally across the land as it once did.
