How people "drowned" New Orleans
The center of New Orleans and the Mississippi River, in the foreground the French Quarter , in the back West Bank , photo from the drone. Authors: Lorenzo Serafini Boni / Emily Jan.
Because of the engineering work, "Crescent City" turned out to be below sea level. Now his future is at stake.
"Below sea level." Firstly, this is a well-known topographical fact about New Orleans, and secondly, the world's media to nausea often scoffed in a similar way after the impact of Hurricane Katrina in 2005. Locals usually mention this detail, combining a sullen grin with anxiety out of town.
In addition, it is only half true. The good news is that depending on where the line is drawn, more than fifty percent of the New Orleans agglomeration actually lies above sea level. The bad news is that earlier “over” were one hundred percent, before engineers accidentally “drowned” half of the city. The intentions, of course, were good, and it was believed that this could solve one old problem. Alas, instead created a new, and much larger scale.
Three hundred years have passed since the spring when French colonists began cutting down vegetation in order to found La Nouvelle-Orléans on a scanty natural dam washed by the Mississippi River. Only three or five meters above the water's mirror, this piece of land was almost the only exalted place in the region, among swamps and swamps. Someone from the French then described it as "two narrow strips of land, the width of a musket shot, surrounded by impassable bogs and thickets of sugarcane."
After the founding of New Orleans in 1718, the city grew for two hundred years, and nothing remained but to master this meager coast - therefore, in local history, from city and geographical names to architecture and infrastructure, many names echo the surrounding terrain.
New Orleans and its surroundings in 1863. A growing city lonely clings to the bend of the Mississippi River. Source: Wells, Ridgway, Virtue, and Co. / Library of Congress.
This may seem paradoxical to anyone visiting the Crescent City. What is the "relief"? We are in one of the most flat places in the region, how can we give so much importance to the “hills”? But this, in fact, is the essence: the smaller the resource, the higher its value. Unlike other cities, where elevation drops can be tens of meters, in New Orleans the entire vertical meter can separate what was created in the time of Napoleon from what was built next door during the jazz era or the space age.
In order to understand how these features of the landscape grew and why they later “sank”, we are forced to go far into the past, straight into the Ice Age, where melting glaciers drove sedimentary deposits along the Mississippi to the Gulf of Mexico. About 7,200 years ago, the mouth of the river began to crush the sea, dumping the rock faster than tidal activity and currents could erode it. Nanos accumulated, and lower Louisiana gradually appeared on the Gulf coast.
The zones along the channel and tributaries turned out to be maximally elevated, because the largest amount of coarse-grained rock was deposited there. Farther from the river, mostly mud and clay fell, therefore here the soil only slightly rose above the level of the pestilence, turning into swamps over time. The farthest areas received meager doses of building material and, being among brackish tides, became wetlands or salt marshes. Under natural conditions, the entire delta of the river lay generally above sea level, from a few centimeters on the coast, to a few tens of meters in the bend of the river that formed the natural dam. Nature has built a lower Louisiana above sea level, albeit in part - and not for good.
Aborigines mostly adapted to constant flooding, strengthening the coast or moving to high ground during floods. But a little later, the Europeans arrived to colonize these lands. Colonization means constant presence, and consistency means engineering to stabilize this soft and moist landscape: dams to hold water, channels to drain the soil, and eventually, pumps to pump water from canals enclosed by flood- control walls .
All this will need to be cultivated for decades and centuries to bring to mind. Until then, during the periods of colonial rule of France and Spain, and before Louisiana moved to American Dominion in 1803, the New Orleans had no choice but to cram into these two “narrow strips of land”, carefully avoiding the rest of the “impassable swamps and thickets sugar cane. People hated every inch of the swamp, seeing it as a source of putrid fumes, a cause of disease and a constant threat to prosperity. One columnist in 1850 described it this way: “This bubbling fountain of death is one of the most dreary, depressive and disgusting places over which the sun ever shone. And all this, under tropical heat, belching poison and malaria ... a concentrate of seven Egyptian executions ... covered with yellow-green abomination. "
It was only much later that people learned that diseases like yellow fever are caused not by marsh fumes, but by the bites of mosquitoes of the Aedes aegypti species , carried with transatlantic voyages; that mosquitoes have proliferated due to urban drainage systems and low sanitation; that this “depressing and depressive” locality has in fact helped to store water for centuries, from wherever it flowed - from the sky, from Mississippi, Poncharthrain Lake or the Gulf of Mexico. And there is nothing "disgusting", just in those days, no one has yet lived in a swamp, as there was no drainage technology. And most importantly - this "yellow-green abomination" was above sea level.
Understanding perfectly well that urbanization doesn’t really fit with the natural behavior of the river delta, in New Orleans they dug drainage canals and filled dams from the very day the city was founded. One of the colonists in 1722 said that the settlers were charged "to leave a strip of land no longer three feet wide in the plot where the ditch should be dug in order to drain the soil." Diversion canals were made in order to speed up drainage back to the swamps, and they were dug in nearby plantations to monitor soil salinization or drain water to the mills.
The main driving force of these engineering structures, of course, was gravity, but in the early 1800s, steam energy came to the market. In 1835, New Orleans Drainage Company began digging through a network of city gutters, and for pumping sewage back to the St. John's ductused steam pumps - and even partially succeeded. A similar pumping system was built in the late 1850s, but the Civil War interrupted the development of the initiative. In 1871, the Mississippi and the Mexican Gulf Ship Canal Company dug out about fifty miles of drainage, including three central drains, before bankruptcy.
It became obvious that the drainage of New Orleans is best done at public expense. State engineers in the late 1800s tied together the cobbled bridges and gutters that had reached them, added several steam pumps, and thus were able to divert about 40 millimeters of daily precipitation back to the surrounding waters.
Of course, this was not enough to drain the swamps, but enough to gradually raise the surface of New Orleans. We know this because in 1893, when the city finally decided to get down to business seriously and hired expert engineers to solve the problem, a heights scheme was created that had never been compiled before. The resulting topographic map of New Orleans (1895) can give an idea of the emergence of what would later become a world-class system.
The contour map of New Orleans, created in 1895 as part of attempts by city authorities to solve the problem of drainage. Source: Courtesy of the New Orleans Public Library
The 1895 map also showed something curious: for the first time, the distant surroundings of some suburbs sank just below sea level. And such a drawdown did not promise anything good afterwards.
So began the anthropogenic lowering of the soil - the earth "drowned" in the ground because of human actions. When the floods stopped and artificial dams restricted the spill, the groundwater level dropped, the soil dried out, and the vegetation began to fade. After that, air pockets formed in the thick of the ground, where particles of clay, sand and salt gradually subsided, pressed together - and pulled the city down.
The construction of a new drainage system began in 1896 and by 1899 was in full swing, as the new property tax was unanimously approved(note: two-mill property tax - taxed at $ 2 every thousand dollars of the market value of the property. For example, if the property is valued at $ 4000, then the two-mill property tax will be $ 8)to create New Orleans Sewerage and Water Board. In 1905, about 60 kilometers of new canals and gutters were dug, hundreds of kilometers of pipes were laid and six pumping stations were built with a capacity of about 150 cubic meters of water per second. Radically, the efficiency of the system increased in 1913, when a young engineer, Albert Baldwin Woods, developed huge impeller pumps that could pump water much faster. Eleven "Woods screw pumps" installed in 1915, and most of them are still working. By 1926, about 120 square kilometers of soil were drained, thanks to almost a thousand kilometers of pipes and ditches, capable of draining about 370 cubic meters of water per second. New Orleans finally defeated swamp.
Urban geography has seriously changed. Within a decade or so, where the marshes used to be, a suburb appeared. Property prices skyrocketed, taxes swelled, and the city spread downstream along Lake Ponchartrain. “All city organizations” celebrated a victory over nature, wrote John Magill, a local historian. "The developers encouraged expansion, newspaper workers glorified, the development planning commission sang ode to it, the city was built by trams to service it, and banks with insurers poured money on the river." The white “middle class”, passionately wanting to leave the old shabby suburbs, massively moved to new areas “on the shore of the lake”, not allowing black families to settle there through discriminating covenants .
«долгое время существовали ковенанты относительно расовых меньшинств. Комитет по гражданскому единству в публикации от 1946 года определил расово запретительные ковенанты так: соглашение внутри группы владельцев собственности, застройщиков участков или пользователей некоего недвижимого имущества в выделенном районе, требующее от них не продавать, не сдавать в аренду и лизинг, или не передавать другим любым способом своё имущество людям с определёнными расой, цветом кожи или вероисповеданием, в течение оговорённого периода времени; исключением может быть только случай единогласного одобрения такой сделки». Источник: http://depts.washington.edu
And these places have already been rebuilt not on stilts above the ground, but on a stone foundation, rejecting two centuries of local architectural traditions. Why bother with flooding if technology has solved this problem?
Drawing screw Woods pump. Source: US Patent 1,345,655
Changes in topography were small, but continuous. The whole city was above sea level in 1800, then only by 95 percent in 1895, and by 1935 only 70 percent was “above”.
Lowering the terrain continued the more, the more people moved to the lower reaches. In 1900, approximately 300,000 inhabitants lived above sea level, and when the population had grown to 6,57525 by 1960, only 48 percent remained “above”. By this time, about 321,000 residents lived in the former swamp, which had turned into a group of “bowls” with a bottom one or two meters below sea level.
To the average New Orlean of those years, this seemed like a kind of local "feature." And, as then, it is still unclear to many that the situation was not so long ago and solely due to the actions of a person, and there is a lot of danger in it. But bridges constantly jars, and buildings crack. In 1965, after the hurricane "Betsy" broke through the dam and flooded four urban areas, and the "feature" more began to resemble a "catastrophe."
Sinking of soil led to frightening consequences in the 1970s when, without warning, at least eight who had no problems with the current maintenance of buildings took to the air. "To the majority of Metari residents," wrote the newspaper The New Orleans Times-Picayune, "It is extremely curious how long they lived for God knows how many time bombs." The area, which was initially low and was located mainly on the former peatlands, was drained just a decade earlier. A huge amount of "wet sponge" dried up, as a result, the soil "shrank" and caused the destruction of the foundations. And in some cases, the gas pipes were interrupted and the gas slowly leaked into the basements, after which there was just enough a small spark.
The emergency was smoothed out with the help of regulations requiring the use of pile foundations and flexible connections in communications supplies. But the larger problem only aggravated, because the gardens, streets and parks continued to subside, and those neighborhoods that adjoined the surrounding water bodies were required to be equipped with new drainage channels and flood-prevention walls. Most of these systems, including those of federal significance, turned out to be unfinished, under-funded and under-verified, and too many of them did not withstand the impact of hurricane Katrina on August 29, 2005. The result of all this “topographic history” was sad when the sea broke through the barricades and flooded the cup-shaped areas with salt water, in places to a depth of four meters. The massive loss of life and catastrophic destruction is the result of
The elevation modeling in New Orleans, obtained using LIDAR , shows areas above sea level in red tones (up to 3 or 5 meters, except for artificial dams) and below sea level in tones from yellow to blue (mostly from -0.3 to -3 meters). Source: Richard Campanella / FEMA
What to do? Sinking of urban development will not turn back. Engineers and planners cannot “inflate” the compacted soils if buildings are already built on them and people live on them. But they can reduce, and perhaps stop, the "sinking" of the terrain through slowing down the drainage of wastewater throughout the city in order to preserve as much water as possible on the surface, thereby feeding groundwater and filling air cavities.
The concept of the operation of such a scheme is set forth, for example, inGreater New Orleans Urban Water Plan , proposed by local architect David Waggonner in collaboration with colleagues from Holland and Louisiana. But even if such measures are carried out completely and completely, it is still impossible to lift those areas that have already sunk. Consequently, the agglomeration of New Orleans, along with the rest of the population of the country, must allocate funds for maintenance and improvement of barrier structures that prevent water from entering the “cup”.
To some extent, resources have already been received after Katrina, when the US Army Corps of Engineers quickly conducted the development and construction of a System that reduces the risk of damage from hurricanes and storms.(Hurricane and Storm Damage Risk-Reduction System, HSDRRS). Completed by 2011 and costing more than $ 14.5 billion, the complex or, as the locals call it, “The Wall”, stretching for many kilometers, was designed to protect the population even from floods of such a storm, which appear with a probability of no more than 1% in any arbitrarily selected year - even taking into account the fact that such a level of security is excessive, the system will continue to be improved.
Nevertheless, we know from history that the “walls” (that is, dams, embankments, flood walls and other solid barriers) caused problems with the relief in New Orleans, despite the fact that they were important for this. a three hundred year urban experiment in the Mississippi Delta. The city cannot rely only on such measures. The most important and important direction for ensuring a calm future in this region is support for structural changes in conjunction with non-structural approaches.
Since the 1930s, the Louisiana coast has been eroded over an area of more than 5,000 square kilometers, mainly due to the erection of the Mississippi River and the excavation of ditches for oil and gas pipes, as well as navigable canals - not to mention the rising sea level and the salt invasion. water. To reduce losses can be due to the same property of the Mississippi River, which built this landscape; if freshwater is diverted and the sediment transported by it is pumped to the coastal plain, in this way it is possible to squeeze the advancing salt water and strengthen the wetlands in less than the sea.
Restored wetlands will prevent waves from catching up with hurricanes, weakening and reducing them before they reach the Wall, thus reducing the risk of a breakthrough and flooding of the bowl. Plan providedThe Office for the protection and restoration of coastal areas (Coastal Protection and Restoration Authority, CPRA ) and supported by the government at the state level, fully endorsed and accepted the work, and some projects are already in the process. But a greater amount of work is comparable with the flight to the moon, since the costs can be at least 50 billion dollars, and the costs will surely double. In the meantime, there is only a small part of the above amount.
In the meantime, people will have to raise their homes above the baseline flooding mark (a necessary requirement for receiving federal flood insurance). If finances allow, it is, of course, preferable for them to move to the half of the metropolis, which remains above sea level. By joining together, residents could focus on promoting Urban Water Plan, supporting coastal restoration activities, and understanding global causes for rising sea levels.
And yet, they should have cut themselves off from the further drainage of any other wetlands for the sake of the development of the city. We must allow the marshes and swamps to turn green with grass and fill with blue water, become an absorber for heavy rains and a buffer for storm waves - and let their height be at least a little, but above sea level. After all, when living things happen to be “below sea level,” as New Orleans, there are not too many options besides adaptation.