Conspiracy of the levees: the latest battle of New Orleans.
Even though much of New Orleans (including the Bywater) is a bit decrepit, I had never seen the city in such disarray. Street lights and fallen oak trees littered the median and every car along the curb had a window broken out and its trunk popped. Abandoned city buses, parked at odd angles, mocked the failed evacuation effort. Two empty schools had all their windows thrown open to permit ventilation for the evacuees who had huddled there in the dark during the perilous days before we arrived. Toward Lake Pontchartrain, water stood up to a meter deep in the streets. Facing south toward the Mississippi River, the streets were largely dry.
St. Claude Avenue and the Bywater had endured high winds and rising water as Hurricane Katrina pounded ashore the preceding Monday, but its residents and landscape did not suffer like its neighbor across the Industrial Canal, the Lower 9th Ward. To the uninitiated, New Orleans appears topographically barren, a featureless surface. No ridge, no mountains, not so much as a hill, other than the human-made levees that encircle the city. Although seemingly flat, there is sufficient relief in the city to direct the movement and collection of water when it overwhelms the massive barriers built to protect the city. The story of flooding in New Orleans following Hurricane Katrina is thoroughly tied up in the story of the flood protection levees.
In short, the levees provided a false sense of security, contributed to the subsidence of neighborhoods that they helped protect, and ultimately encouraged inappropriate development in the most vulnerable neighborhoods. Thus they conspired with the drainage works, subsiding soils, public officials, and developers to create a situation exploited by a powerful hurricane.
An Inverted Landscape
Long before Katrina arrived, Native Americans and French settlers faced floods from the river and from hurricanes. Unlike city sites in Europe, where land typically slopes up from a river's bank, the highest ground in New Orleans was immediately adjacent to the river. At the location selected for the colonial capital in 1718, the river had built a shoulder of high ground that was four or five meters above sea level along both banks. Regular murky floods slowed as they escaped the channel, dropped larger sediments on this land (known as the natural levee), and added ever so slightly to its height. As the annual flood waters slowed even more away from the river, they deposited finer sediments, creating the "backswamp." This natural sorting produced a gentle incline that sloped away from the river toward the cypress swamp, which graded to marsh near sea level and Lake Pontchartrain. Thus, the best farm land, urban soils, and highest land crowded near the source of its sediments--the river.
Although unaccustomed to this peculiar terrain, the French learned from the native Americans that it made great sense to build on the high ground near the river. Jean-Baptiste Le Moyne de Bienville, the colonial governor, selected a site for his capital that was a portage location for Native travelers and that linked the river with the lake. He nonetheless admitted the flood hazard, writing in 1720, "the river which overflows almost every year, is cause of great inconvenience and damage to many houses built too close to the waters."
To fend off the regular inundations, the colonial government began building low earthen barriers, which they called levees. Linear mounds of dirt a meter or so high soon stood as a somewhat wishful impediment to river floods. Until the levees reached the first high ground, about 160 kilometers upstream at the site of present-day Baton Rouge, floods escaping the channel upstream could still creep into the city's rear quarters from the overflowing backswamp. In order to extend the barrier, the colonial government enacted a law requiring individual land owners to erect their own levees. Similar to courvee labor used to maintain roads in France, this requirement placed the cost of protecting New Orleans on rural planters. Continued by the Spanish after they acquired the colony in 1763, private levee building succeeded in extending the levees to Baton Rouge by the end of the colonial period.
But still, protection was wanting. There was no consistency in the design and strength of privately built structures and maintenance was erratic. So despite an erstwhile flood protection system, it was insufficient to ward off the mighty Mississippi. A major flood broke through the levee and delivered high water to the new American port of New Orleans in 1816, and parts of the city remained under water for a month. Contemporary accounts noted that there was inequity in the vulnerability of different social groups. The wealthy Creoles and newly arrived Anglos clustered on the highest ground. Laboring immigrants took up residence on the edge of the backswamp. According to Edward Fenner, an observer of the event, the "inundation has driven many poor families from their homes." In an era without federal disaster relief, he called on the affluent to come to the aid of their less fortunate fellow citizens to prevent greater distress caused by "poverty, famine, and perhaps pestilence."
A similar flood washed over the city again in 1823, followed by an even greater event in 1849 that underscored both the frailties of the levees and the lingering inequities in impacts. The levee at the Sauve plantation upstream gave way, and water careened off Metairie Ridge, a relict river in which sedimentary deposits had created a crescent-shaped natural levee (see map, p.11). The water took dead aim at the low tracts nearly encircled by the slightly higher levee, and quickly filled this area, which became known as the bottom of the bowl, to a depth of two meters. Water surrounded 200 square blocks containing about 2,000 homes and displaced 12,000 of the 116,000 residents. One observer wrote that the poor were forced "to live an aquatic life of privation and suffering" during the 40-day inundation.
In response to this flood, like others before and after, officials raised the levee height and thereby encouraged additional urbanization on the floodplain. Armed with a false sense of security, leaders and citizens alike refused to concede an inch to the river. By the 1860s they had heaped up a largely impenetrable bulwark between New Orleans and the river. Nonetheless, the inverted topography allowed floodwaters to outflank the city's barrier when a weak link in the chain broke upstream. "Backdoor" flooding continued from the river through 1890.
Ultimately, the Mississippi River Commission and the U.S. Army Corps of Engineers, which assumed primary levee building responsibilities in 1879, erected a much more effective flood protection system. Although there were massive failures upstream during the unprecedented flood of 1927, New Orleans remained untouched. Responding to the 1927 event, levee strengthening remained a key part of the plan. The Corps took a lesson from nature and designed two artificial outlets, controllable floodways that could be opened during high water to divert excess flow to the Gulf of Mexico, much like the numerous distributary bayous had done before the levees severed them from the river. The river levees in the lower course of the river have not permitted a flood at New Orleans and give the impression that they are infallible. These levees also contribute to coastal land loss by directing over 100 million tons of sediment into the deep Gulf of Mexico annually. Without the levees, flooding would have continued to add sediments to the slowly sinking delta.
It is unlikely that the current sediment load could keep pace with subsidence, however. Today the Mississippi River carries only about 20 percent of the sediments that it transported in the 1950s. Of course, without levees New Orleans would have endured regular inundations and the river likely would have abandoned its current channel in favor of the Atchafalaya River. Turning the river loose would not have ensured that it would stay in its present course. New Orleans has endured in its inauspicious site because of the levees, but now those levees are seen as a big part of the problem.
Closing the Back Door
While engineering works eliminated "front door" flooding, preventing water from entering via Lake Pontchartrain took longer, for two main reasons: the greater frequency of river floods meant that public attention and resources were focused on solving that more troublesome problem first. Second, few people lived on the lake side of the Metairie Ridge before 1900. So although both backdoor river floods and hurricane-driven surge could wash over the lake-fringing wetlands, anyone who lived there occupied a stilt house. Flood protection was the responsibility of those who chose to reside in harm's way.
Residential crowding of the narrow natural levee prompted efforts to reclaim the wetlands on the lake side of the narrow ridges in the 20th century. To provide for an expanding urban footprint, in 1900 the city commenced a multifaceted public works program that sought to extend sewage and water supplies to all sections of the city. Equally important was a separate drainage system, for without artificial help storm runoff, overflow from privies, and other liquids would flow only as far as the backswamp or navigation canals. Empty lots and canals resembled open-air septic troughs. To remove this offensive urban residue, the city's engineers planned a massive set of drains that would direct the city's liquid effluent to the lowest areas, from where pumps would propel it into a nearby saltwater bay, Lake Borgne. Drainage and the other public works made it possible to expand residential neighborhoods toward the lakefront.
In 1915, a major hurricane blew over the city and gave pause to the rush toward the lakefront. This unnamed storm pushed a storm surge two meters high into the lakefront wetlands. Water rushed up Bayou St. John and left well over two meters of water in the bottom of the bowl. The mass of water overwhelmed the city's new pumps and contributed to the damage of 20,000 buildings. In response, the city commenced construction of a concrete seawall to block future surges blown in from the lake, completing the impressive structure by 1934. In adjacent Jefferson Parish, the state built a raised highway along the lakefront, where its two-meter-high roadbed provided protection for the city's suburban neighbor.
These barriers were in place when the next major hurricane pummeled New Orleans in 1947. Considerable development had occurred behind the seawall in Orleans Parish, and returning World War II veterans were purchasing lots and building homes in Jefferson Parish. With gusts estimated at well over 180 kilometers per hour (kph), the tropical cyclone overtopped the seawall and pushed the surge into many homes in the lakefront neighborhoods. Damage was considerable in Jefferson Parish since the low roadbed had subsided and flood waters simply pooled for a couple of weeks behind the highway berm fronting the lake.
As with previous floods, public officials embarked on programs to raise the levees rather than re-think their basic strategy. The commitment to levees was unwavering. Hadn't they conquered the Mississippi River and kept it out of the city for three-quarters of a century? But a pair of storms in the 1960s clearly demonstrated their adjustments were insufficient. Hurricane Hilda (1964) caused damage to camps along the city's lakefront, to poorly protected districts in eastern New Orleans, and to industries along the Industrial Canal. Although impressive, Hilda quickly faded from memory after Hurricane Betsy made landfall in September 1965. Barreling inland just west of the Mississippi River, Betsy produced winds in excess of 180 kph and pushed a storm surge up the newly completed Mississippi River-Gulf Outlet, a shortcut for ocean-going ships to the port of New Orleans. Water broke through the levees along the Industrial Canal and produced severe flooding in neighborhoods flanking the canal, the Lower 9th Ward, and the Bywater district. As a preview to Katrina, rising water forced many to climb into dark attics, tear holes in their roofs, and sit in the hot sun the next day awaiting rescue.
With over 27,000 homes flooded or destroyed in the region, local politicians called for massive levee improvements for the city, the population of which had grown to more than 600,000 citizens. Governor John McKithen pledged that he would "see that nothing like this happens in our state again" and asked Congress to take steps that would "make a repeat of this disaster impossible." In short order Congress authorized a pre-existing plan for the Corps of Engineers to build larger levees that would fend off the surge driven by a storm with 160-kph winds. Work began the following year and continued on through 2005. Higher levees remained
the key element of the protection system that lined the lake, areas on the lower river delta, and ultimately wetlands on the west bank of the Mississippi River as well. With a few exceptions, this system, which was still under construction last year, prevented massive flooding--until August 2005.
A Sinking Feeling
The conspiracy of the levees comes into sharp focus when one looks at the areas of land surrounded by hurricane protection levees in south Louisiana. With the exception of acreage on natural levees, tracts encircled and drained have subsided below sea level. Thus when waters break through or overtop the levees, the levees act as impoundments and effectively lengthen a flood's duration. Pumps must perform the work of gravity and lift the water back up to sea level to prevent usable real estate from becoming crawfish ponds.
Ambitious entrepreneurs first encountered this phenomenon in Louisiana in the late 19th century. Several attempts to drain wetland soils, thought to be immeasurably productive farm land, were undertaken to create agricultural empires in the marsh. All ended in failure as the land sank beneath the water table. The infamous Delta Farms in nearby Lafourche Parish is nothing more than a huge rectangular lake on state maps--not the seat of thriving agribusiness. Other lesser projects in the New Orleans area provided additional evidence of subsidence. The peaty soils of the Mississippi River delta need moisture to hold them in place and to prevent oxidation of the peat. Drainage removes the vital hydraulic support and the peat oxidizes, allowing the land surface to subside. In addition to the croplands turned to lakes, the subsiding roadbed along the lakefront and levees throughout the region were dramatic reminders of this process when storms arrived.
Nonetheless, optimistic developers of the 1920s suburbs of lakefront New Orleans and of the post-war sprawl in Jefferson Parish ignored the critical evidence and pushed the urban frontier closer and closer to the lake's edge. Eventually, most new subdivisions sank below sea level. As the Corps built its new levees following Hurricane Betsy, the neighborhoods of New Orleans East spread across previously unused lakefront tracts, and local drainage and levee districts installed pumps to drain this valuable new real estate. On the west bank, newly drained wetlands shared a similar fate. In urbanized areas, unlike on farms, the sizable tax base enables the drainage authorities to run their pumps as much as needed and keep the streets and lawns dry, even when they are below the lake level.
In any of the suburban areas, one can stand on top of a hurricane protection levee and eyeball the position of the water in the canals or Lake Pontchartrain at about the same height as the eaves of houses within the barrier's ring. The fact that about half of New Orleans is below sea level is a product of subsidence within the ring of levees. Without levees, there would have been no pumping, no drainage, and much slower subsidence. Drainage without levees would have let the lake creep to the relict ridges that protected the city during the colonial era. The conspiracy cannot succeed without the collaboration of pumps and levees--and public officials who approve of these efforts, and developers who sell the lots, are co-conspirators.
By the late 1970s, the subsidence and a spate of heavy rain storms exposed new problems in the Crescent City. A series of downpours overwhelmed the city's pumps and produced extensive flooding even without the assistance of a hurricane or the Mississippi River. Residents who claimed they'd had no flood damage in 30 years were mopping their floors repeatedly in the 1980s. By 1995, public officials in Orleans and Jefferson parishes forged a new and unprecedented alliance with the Corps of Engineers to improve the urban drainage system. Designed and built by the Corps and its contractors, enlarged drainage canals and massive pumps offered a final adjustment to what had become a combined river, hurricane, and rainfall flood protection system.
The Eve of Destruction
There were numerous local organizations and agencies that had a role in levee-making decisions, finance, and maintenance, but the Corps remained the most visible participant. It is important to keep in mind it is a federal agency that had only reluctantly accepted orders to build river flood protection levees in the 19th century. Although ultimately the Corps' responsibilities expanded during the 20th century, in August 2005 pumping responsibility rested with local authorities in each parish.
Neither the pumps nor the levees stood up to Katrina's surge. As the levees failed, whether due to breaching or overtopping, water filled the bowl and New Orleans became the Bay of Orleans. After the storm passed, the lake level fell and water poured back out of the breaks to the level of the breaches. Temporary pumps then gradually transferred excess water back into the lake from the ground lower than the lip of the bowl.
As bad as it was, Hurricane Katrina did not cause the worst-case scenario. Forecasters have long proclaimed that the unthinkable event would be a Category 4 or 5 storm overtopping the levees without breaching them. In that situation, water would stand as deep as six meters, not two or three. If the levees were to hold, gravity would not assist in lowering the water and flood conditions could last for months. Although the Corps is restoring and strengthening the levees, these barriers still have design limits and will not prevent flooding from a Category 4 or 5 storm. Massive effort that it is, the levee repairs that are under way merely perpetuate the conspiracy of the levees.
Structural solutions to hazardous events are seldom resilient. With so much of the city vacated and only a fraction of its population back in residence, New Orleans has the opportunity to weave resiliency into the fabric of its future. By creating open spaces in the lowest areas within the ring of levees, where water can collect during the next flood rather than filling peoples' living rooms, the city can ensure a higher degree of safety and avoid the massive costs of rebuilding flood-prone structures exposed to high water. By working with state and federal officials to restore the wetland buffer around Louisiana's southeastern coast, the city can augment the levees and dampen the next storm surge. Land use adjustments and wetland restoration can add a degree of resiliency to the existing structural defenses. Without such measures, a Son-of-Katrina sequel is all but inevitable.
Craig E. Colten is the Carl O. Sauer Professor of Geography at Louisiana State University.
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|Author:||Colten, Craig E.|
|Date:||Sep 1, 2006|
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