Half of New Orleans is at or above sea level according to the study by Tulane and Xavier universities’ Center for Bioenvironmental Research. The parts of the city that are several feet above sea level include, but are not limited to: the River Bend, Audubon/University, Uptown, the Garden District, the French Quarter, Treme, Bayou St. John, the Marigny, Bywater and the Lower Ninth Ward. The original residents settled on the high ground along the Mississippi River. Later developments eventually extended to nearby Lake Pontchartrian. Navigable commercial waterways extended from the lake to downtown. After 1940, the state decided to close these waterways since there was a new Industrial Canal for waterborne commerce. Once these waterways were closed, the water table was drastically lowered by the city’s drainage system and some areas settled several feet due to the consolidation of the underlying organic soils. After 1965, the US Army Corps built a levee system around a much larger geographic footprint that included previous marshland and swamp.