How Humans Sank New Orleans - The Atlantic

B A W Y RECOMMENDED READING 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) TECHNOLOGY HOW HUMANS SANK NEW ORLEANS Engineering put the Crescent City below sea level. Now, its future is at risk. By Richard Campanella FEBRUARY 6, 2018 elow sea level . It’s a universally known topographical factoid about the otherwise fl at 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 o ff by half. Depending on where exactly one frames the area measured, roughly 50 percent of greater New Orleans lies above sea level. Th at’s the good news. Th e bad news: It used to be 100 percent, before engineers accidentally sank half the city below the level of the sea. Th eir intentions were good, and they thought they were solving an old problem. Instead, they created a new and bigger one. Th ree hundred years ago this spring, French colonials fi rst 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.” For two centuries after the establishment of New Orleans in 1718, urban expansion had no choice but to exploit this slender ridge—so much so that many patterns of local history, from urbanization and residential settlement geographies to architecture and infrastructure, spatially echoed the underlying topography. New Orleans and its vicinity in 1863. The developing city tightly hugs the ridge nearest the Mississippi River. (Wells, Ridgway, Virtue, and Co. / Library of Congress) Th is might seem paradoxical to anyone who’s visited the Crescent City. What topography? In one of the fl attest regions on the continent, how can elevation matter so much? But that’s exactly the point: Th e 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 di ff erence 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 runo ff down the Mississippi to the Gulf of Mexico. Starting around 7,200 years ago, the river’s mouth began pressing seaward, dumping sediments faster than currents and tides could sweep them away. Th e mud accumulated, and lower Louisiana gradually emerged from the Gulf shore. Areas closest to the river and its branches rose the highest in elevation, because they got the most doses of the coarsest sediment. Areas farther from the river got just enough silt and clay particles to rise only slightly above the sea, becoming swamps. Areas farthest out received scanty deposition of the fi nest particles amid brackish tides, becoming grassy wetlands or saline marsh. Th e 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. Nature built lower Louisiana above sea level, albeit barely—and mutably. ADVERTISEMENT Native peoples generally adapted to this fl uidity, shoring up the land or moving to higher ground as fl oodwaters rose. But then European imperialists came to colonize. 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 fl oodwalls. ll this would take decades to erect and centuries to perfect. 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 [and] 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. One observer in 1850 unloaded on the wetlands: “ Th is boiling fountain of death is one of the most dismal, low, and horrid places, on which the light of the sun ever shone. And yet there it lies under the in fl uence of a tropical heat, belching up its poison and malaria ... the dregs of the seven vials of wrath ... covered with a yellow greenish scum.” Only later people would learn that it was not miasmas but the invasive Aedes aegypti mosquito, brought in by transatlantic shipping, that caused diseases like yellow fever; that it was urban cisterns and poor sanitation that enabled mosquitoes to breed and feed on human blood; and that the “dismal, low” terrain actually aided the city by storing excess water, be it from the sky, the Mississippi River, the bay known as Lake Pontchartrain, or the Gulf of Mexico. It was not “horrid” but propitious that nobody lived in the backswamp, and that the technology to drain it was not available. And most importantly, that the “yellow greenish scum” lay above sea level. ADVERTISEMENT Understandably, given the incompatibility of natural deltaic processes with urbanization, New Orleanians began erecting embankments along the river and digging drainage ditches within a year of the city’s foundation. One colonist described how settlers in 1722 were “ordained [to] leave all around [their city parcel] a strip at least three feet wide, at the foot of which a ditch was to be dug, to serve as a drain.” Out fl ow canals were excavated to speed drainage back toward the swamp, and in nearby plantations, ditches were dug to control soil water or divert river water to power sawmills. Gravity was the main source of energy for these initial water projects, but in the early 1800s, steam power came into the picture. In 1835, the New Orleans Drainage Company began digging a network of urban ditches, using a steam-driven pump to push the runo ff back out of Bayou St. John—with limited success. A similar pumping system was attempted in the late 1850s, only to be disrupted by the Civil War. In 1871, the Mississippi and Mexican Gulf Ship Canal Company dug 36 miles of ditches, including three major outfall canals, before it too went bankrupt. It was becoming clear that draining New Orleans would best be stewarded by the public sector instead. Municipal engineers in the late 1800s cobbled together the extant network of gutters and ditches and, with the propulsion of some steam-driven pumps, were able to expel up to one-and-a-half inches of rainfall per day into surrounding water bodies. ADVERTISEMENT Th at wasn’t nearly enough to drain the swamp, but it was enough to begin permanently altering the New Orleans’s land surface. We know this because in 1893, when the city fi nally got serious and funded expert engineers to fi gure out how to solve this problem, surveyors set out to map local elevations as had never been done before. Th e resulting topographical map of New Orleans (1895) would inform the engineering of what would become a world-class system. Contour map of New Orleans, produced as part of the city’s 1895 effort to finally solve the drainage problem (Courtesy of the New Orleans Public Library) Th e 1895 map also revealed something curious: Th e rear precincts of one downtown faubourg had, for the fi rst time, dipped slightly below sea level. Th e sinkage would not bode well for things to come. hat was beginning to happen was anthropogenic soil subsidence —the sinking of the land by human action. When runo ff is removed and arti fi cial levees prevent the river from overtopping, the groundwater lowers, the soils dry out, and the organic matter decays. All this creates air pockets in the soil body, into which those sand, silt, and clay particles settle, consolidate—and drop below sea level . ADVERTISEMENT Construction of the new drainage system began in 1896 and accelerated in 1899, when voters overwhelmingly approved a two-mill property tax to create the New Orleans Sewerage and Water Board. By 1905, 40 miles of canal had been excavated, hundreds of miles of pipelines and drains had been laid, and six pumping stations were draining up to 5,000 cubic feet of water per second. System e ffi cacy improved dramatically after 1913, when a young engineer named Albert Baldwin Wood designed an enormous impeller pump that could discharge water even faster. Eleven “Wood screw pumps” were installed by 1915, and many are still in use today. By 1926, over 30,000 acres of land had been “reclaimed” via 560 miles of pipes and canals with a capacity of 13,000 cubic feet of water per second. New Orleans had fi nally conquered its backswamp. Th e change in urban geography was dramatic. Within a decade or so, swampland became suburbs. Property values soared, tax co ff ers swelled, and urbanization sprawled onto lower ground toward Lake Pontchartrain. “ Th e entire institutional structure of the city” reveled in the victory over nature, wrote John Magill, a local historian. “Developers promoted expansion, newspapers heralded it, the City Planning Commission encouraged it, the city built streetcars to service it, [and] the banks and insurance companies underwrote the fi nancing.” Th e white middle class, eager to fl ee crumbling old faubourgs , moved into the new “lakefront” neighborhoods en masse, to the point of excluding black families through racist deed covenants. And in a rebuke of two centuries of local architectural tradition, new tract housing was built not raised on piers above the grade, but on concrete slabs poured at grade level. Why design against fl oods if technology has already solved that problem? Design plans for a Wood screw pump (U.S. Patent 1,345,655 ) Th e change in topographic elevation was more subtle, but equally consequential. A city that had been entirely above sea level into the late 1800s, and over 95 percent in 1895, had by 1935 fallen to about 70 percent above sea level. ADVERTISEMENT Subsidence continued even as more and more people moved into subsiding areas. While the vast majority of New Orleans’s 300,000 residents lived above sea level in the early 1900s, only 48 percent remained above the water in 1960, when the city’s population peaked at 627,525. Th at year, 321,000 residents lived on former swamp, over which time they dropped into a series of topographical bowls four to seven feet below sea level. Th e average New Orleanian of this era perceived being below sea level as something of a local curiosity. Th en as now, most folks did not understand that this was a recent man-made accident, or that it could become hazardous. But streets increasingly buckled and buildings cracked. When Hurricane Betsy ruptured levees and fl ooded the bottoms of four sunken urban basins in 1965, the curiosity became more of a crisis. Soil subsidence made frightful headlines in the 1970s, when at least eight well-maintained houses in a suburban subdivision exploded without warning. “Scores of Metairie residents,” Th e New Orleans Times-Picayune reported , “wondered whether they are living in what amounts to time bombs.” Th e a ff ected subdivision, low-lying to begin with and positioned on an especially thick layer of peat, had been drained just over a decade earlier. With so much “wet sponge” to dry out, the soils compacted rapidly and subsided substantially, cracking slab foundations. In some cases, gas lines broke and vapors leaked into the house, after which all it took was a fl icked light switch or a lit cigarette to explode. ADVERTISEMENT Th e emergency was abated through ordinances requiring foundational pilings and fl exible utility connections. But the larger problem only worsened, as gardens, streets, and parks continued to subside, and those neighborhoods that abutted surrounding water bodies had to be lined with new lateral levees and fl oodwalls. Many of those and other federal structures proved to be under-engineered, underfunded, and under-inspected, and all too many failed in the face of Hurricane Katrina’s storm surge on August 29, 2005. Th e rest is topographic history, as seawater poured through the breaches and fi lled bowl- shaped neighborhoods with up to 12 feet of saltwater. Large-scale death and catastrophic destruction resulted, in part, from New Orleans having dropped below sea level. A LIDAR elevation model of New Orleans shows areas above sea level in red tones (up to 10 or 15 feet, except for the artificial levees) and areas below sea level in yellow to blueish tones (mostly ranging from -1 down to -10 feet). (Richard Campanella / FEMA) What to do? Urban subsidence cannot be reversed. Engineers and planners cannot “rein fl ate” compacted soils if city dwellers have built lives upon them. But they can reduce and possibly eliminate future sinkage by slowing the movement of runo ff across the cityscape and storing as much water as possible on the surface, thus recharging the groundwater and fi lling those air cavities. Th e Greater New Orleans Urban Water Plan , conceived by a local architect, David Waggonner, in dialogues with Dutch and Louisiana colleagues, lays out a vision of how such a system would work. But even if executed fully, the plan would not reverse past subsidence. Th is means that greater New Orleans and the rest of the nation must be committed to maintaining and improving structural barriers to prevent outside water from pouring into “the bowl.” To a degree, those resources arrived after Katrina, when the Army Corps of Engineers fast-tracked the design and construction of a unique-in-the-nation Hurricane and Storm Damage Risk-Reduction System. Costing over $14.5 billion and completed in 2011, “ Th e Wall,” as folks call the sprawling complex, aims to keep those living inside secure from fl ooding from storms computed to have a 1 percent chance of occurring in any given year—not the level of security needed, but an improvement nonetheless. ADVERTISEMENT et , history shows that “walls” (that is, levees, embankments, fl oodwalls, and other rigid barriers) have gotten New Orleans into topographical trouble, even if they have also been essential to the viability of this 300-year-old experiment in delta urbanism. Th e city cannot rely on them alone. Th e biggest and most important part of assuring a future for this region is to supplement structural solutions with nonstructural approaches. Louisiana’s coast has eroded by over 2,000 square miles since the 1930s, mostly on account of the leveeing of the Mississippi River and the excavation MORE FROM METROPOLIS NOW How Will the Future Remember COVID-19? IAN BOGOST Th e YouTuber Who Treats the Inner City Like a Safari STEPHEN KEARSE Th e Pandemic Could End Waiting in Line ELISSAVETA M. BRANDON America Will Sacri fi ce Anything for the College Experience IAN BOGOST SHARE Why Doesn't New Orleans Look More Like Amsterdam? LORENA O’NEIL A Brief History of Levees ADRIENNE LAFRANCE Maybe You Missed It, but the Internet ‘Died’ Five Years Ago KAITLYN TIFFANY MAKE YOUR INBOX MORE INTERESTING Each weekday evening, get an overview of the day’s biggest news, along with fascinating ideas, images, and people. Enter your email Sign Up Sign In Subscribe Popular Latest