Base flood elevation sea level6/29/2023 ![]() ![]() And yet there it lies under the influence of a tropical heat, belching up its poison and malaria. One observer in 1850 unloaded on the wetlands: “This boiling fountain of death is one of the most dismal, low, and horrid places, on which the light of the sun ever shone. In the meantime, throughout the French and Spanish colonial eras, and under American dominion after the Louisiana Purchase in 1803, New Orleanians had no choice but to squeeze their booming metropolis onto those “two narrow strips of land” while eschewing the low-lying “canebrake impenetrable marsh.” Folks hated every inch of that backswamp, viewing it as a source of miasmas, the cause of disease, and a constraint on growth and prosperity. Colonization meant permanency, and permanency meant imposing engineering rigidity on this soft, wet landscape: levees to keep water out, canals to dry soil, and in time, pumps to push and lift water out of canals lined with floodwalls.Ī ll this would take decades to erect and centuries to perfect. But then European imperialists came to colonize. Native peoples generally adapted to this fluidity, shoring up the land or moving to higher ground as floodwaters rose. Nature built lower Louisiana above sea level, albeit barely-and mutably. The entire delta, under natural conditions, lay above sea level, ranging from a few inches along the coastal fringe to over a dozen feet high at the crest of the Mississippi River’s natural levee. Areas farthest out received scanty deposition of the finest particles amid brackish tides, becoming grassy wetlands or saline marsh. Areas farther from the river got just enough silt and clay particles to rise only slightly above the sea, becoming swamps. The mud accumulated, and lower Louisiana gradually emerged from the Gulf shore.Īreas closest to the river and its branches rose the highest in elevation, because they got the most doses of the coarsest sediment. Starting around 7,200 years ago, the river’s mouth began pressing seaward, dumping sediments faster than currents and tides could sweep them away. Understanding how these features rose, and why they later sank, entails going back to the end of the Ice Age, when melting glaciers sent sediment-laden runoff down the Mississippi to the Gulf of Mexico. ![]() Unlike most other cities, which may have elevational ranges in the hundreds of feet, just a yard of vertical distance in New Orleans can make the difference between a neighborhood developed in the Napoleonic Age, the Jazz Age, or the Space Age. What topography? In one of the flattest regions on the continent, how can elevation matter so much? But that’s exactly the point: The lower the supply of a highly demanded resource, the more valuable it becomes. This might seem paradoxical to anyone who’s visited the Crescent City. The developing city tightly hugs the ridge nearest the Mississippi River. ![]()
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