How Humans Sank New Orleans

[Mace]

Engineering put the Crescent City below sea level. Now, its future is at risk.​

The Atlantic
Richard Campanella

Downtown New Orleans and the Mississippi River, with the French Quarter in the foreground and the West Bank in the distance. Lorenzo Serafini Boni / Emily Jan / The Atlantic.

Below sea level. It’s a universally known topographical factoid about the otherwise flat city of New Orleans, and one that got invoked ad nauseam during worldwide media coverage of Hurricane Katrina and its catastrophic aftermath in 2005. Locally, the phrase is intoned with a mix of civic rue and dark humor.
It’s also off by half. Depending on where exactly one frames the area measured, as of early 2018, roughly 50 percent of greater New Orleans lies above sea level. That’s the good news. The bad news: It used to be 100 percent, before engineers accidentally sank half the city below the level of the sea. Their intentions were good, and they thought they were solving an old problem. Instead, they created a new and bigger one.

In the spring of 1718, French colonials first began clearing vegetation to establish La Nouvelle-Orléans on the meager natural levee of the Mississippi River. At most 10 to 15 feet above sea level, this feature accounts for nearly all the region’s upraised terrain; the rest is swamp or marsh. One Frenchman called it “Nothing more than two narrow strips of land, about a musket shot in width,” surrounded by “canebrake [and] impenetrable marsh.”

New Orleans and its vicinity in 1863. The developing city tightly hugs the ridge nearest the Mississippi River. Photo from Wells, Ridgway, Virtue, and Co. / Library of Congress.

This might seem paradoxical to anyone who’s visited the Crescent City. 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. 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.
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......

How Humans Sank New Orleans

Engineering put the Crescent City below sea level. Now, its future is at risk.

getpocket.com

 

[JAG89]

Old news. Anytime the ground water is drawn down, void spaces in the soil where water used to be eventually is compacted. As the soil compact, the ground elevation decreases. Early engineers thought that they were stopping the city from flooding by drawing down its water table, not realizing that they were causing the ground elevation to subside. The ground elevation has subsided so much that a great deal of the City that was above sea level is now below sea level. Now the City has to maintain a certain elevation of ground water at all times, which means the City has various speed pumps that runs all the time, low speed during no rainfall or little rainfall and high speed during heavy rainfall. New Orleans stormwater system is definitely a constant balancing act. Another example that proves that cities are not natural.

 

[JAG89]

Also, because most of New Orleans utilities are submerged in ground water, which creates a higher than normal infiltration/inflow (I/I), New Orleans sewer system flow at full capacity. Therefore, more than likely the system has suction pumps to keep it sewerage water flowing to the City's wastewater treatment facilities.

 

[Mace]

I agree that it is indeed and old Article as well as old News, however, I found the history, graphics and pictures in the Article about one of America's four unique cities very interesting! Thanks for the added info about about the balancing maneuvers that the pumps play!