The Levees Worked in New Orleans — But That’s Not Enough.

Flooding in Lafitte, Louisiana, after Hurricane Ida broke its dikes.
Photo: Tannen Maury / EPA-EFE / Shutterstock

As Hurricane Ida hit New Orleans on Sunday, the Category 4 storm pushed nearly a dozen feet of water from the Gulf of Mexico toward Crescent City, threatening to send the ocean’s contents to spill. in a metropolis that is located for the most part. below sea level. The result would have been catastrophic: the city would have filled with water like a bowl, trapping thousands of inhabitants in their homes.

This is what happened during Hurricane Katrina in 2005, but it did not happen this time. As Ida’s storm surge headed for New Orleans, the water collided with a complex system of dikes and flood walls built by the federal government after Katrina, and the system prevented water to enter the city. Although the hurricane destroyed lots of buildings in New Orleans and knocked the city out complete diet, the worst potential damage was avoided.

The main takeaway for the city, at least according to To Major new securitiesis that the new dam system has passed Ida’s test, with the Washington post saying the system was “firm” against the storm. It is true that the dikes have worked, but the success of the dike system this time is no guarantee that it will hold up next time. Rather than making sure Louisiana residents are safe, this week’s close appeal should make us rethink our reliance on levees and levees – not just in Louisiana but along all of the country’s waterways.

The New Orleans Levee System, rebuilt at a cost of $ 14 billion after Katrina, featured many improvements: The new flood walls are stronger, they are rooted deeper in the ground, and they are designed to resist even if water passes through them. . The Army Corps of Engineers also erected a huge storm barrier around Lake Borgne and closed a channel exit between the river and the gulf, which had channeled the storm surge into the city during Katrina. A spokesperson for the Corps said Bordered Wednesday that the system “worked as expected – it did its job”.

For keen observers of the city’s history, however, this is not enough.

“There is nothing about the fact that the dikes held in this storm that changes the reality that the metropolis of New Orleans sinks into the Gulf of Mexico, the Gulf of Mexico rises, warming water and climate make storms worse, ”said Andy Horowitz, professor to Tulane who has write a book on Hurricane Katrina. “All of these things make it inevitable that at some point the Gulf will return to the city.”

The dike system was only designed to protect against the so-called century-old storm, or a storm that has a one percent chance of occurring in any given year. Despite its many design flaws, the old system was designed to protect against a two hundred years storm – a level of protection that Congress did not see fit to match after Katrina. The Army Corps has yet to determine the size of Storm Ida, but we do know that many Category 5 hurricanes would exceed the design capacity of the new system, as will weaker storms if they approached New Orleans by the right way. Recent history shows that storms of such severity are far from rare: in Texas, for example, the past five years have seen the arrival not of one, not two, but Three quinquennial floods, including Hurricane Harvey.

New Orleans’ new system protected the city’s residents this time around, but other Louisians were not so fortunate: several dikes outside of New Orleans failed when Ida had dire consequences.

The most notable failure occurred in the city ​​of Lafitte, just south of town. As Ida rolled north, a massive storm surge of about 12 feet passed the ring of seven-foot-high levees that surround the city of about 2,000 people, inundating nearly every home and every town. companies. The locally maintained town ring that was the product of a sustained lobbying campaign by local leaders, had been completed only last year and aimed to attract long-term investment in the small shrimp town. Ida revealed within hours that the city was far more vulnerable than engineers had assumed: At its peak, the storm surge was almost twice as high as the dikes that were supposed to contain it.

Further east, in the parish of Plaquemines, there were several cases of water overflowing the dikes. The parish resembles a long serpent, with fortified lands on both sides of the Mississippi, and as the wind blew the river back and forth through Sunday night, water poured out on both banks. . On the west bank, it surged through a temporary dike near Alliance Phillips 66 factory, flooding the historic African-American town of Ironton and two other housing estates. On the opposite bank, he broke through another dike and rolled across the Braithwaite village, which was devastated by the storm surge from Hurricane Isaac in 2012.

If the Katrina disaster was the result of shoddy engineering, the dike failures during Ida were the result of a more basic truth about dikes, a truth that is true to some extent of all dike projects. engineering who try to control nature. No matter how high a wall is, nature can always exceed it. The dikes of Lafitte and the parish of Plaquemines were little more than hills of earth built at a certain height: this height represented a kind of compromise between the expectations of engineers concerning future floods and the willingness of politicians to spend money. money for flood protection. As the sea level rises and the ocean warms, and hurricanes get more intense year by year, it is almost inevitable that at some point the water will rise above the walls. of earth in such places.

For a town like Lafitte, whose seven-foot seawall did not match Ida’s height, it may seem like the best answer is simply to build a taller seawall: revise the storm projections upward, determine the new height and stack more soil. This has been the standard response at most levels of government for most century and a half past. As a result, there are now over 3000 miles of dikes in Louisiana and about 3 percent of all people in the United States live in an area protected by an Army Corps flood control structure. In the lower parishes that were slammed by Ida, the Corps has worked for decades to build a chain of dikes and flood gates known as “Morganza in the Gulf“system. When completed, this system will cover almost the entire Louisiana bayou coast. The tallest of these walls will be about 13 feet – high enough to withstand most floods, yes, but not all. The Corps and other agencies have offered similar storm barriers in several other major cities, including New York, Charleston, Miami and Houston.

Obtaining the funds required for adequate protection, however, is easier said than done: In order for the Corps to justify a new project to Congress, it must prove that the total financial benefits exceed costs – in other words, that the structures inside the dike are worth more than the land used to build it. For small towns that are shrinking along the Gulf Coast, that math doesn’t get any easier, and indeed there are a few places along the coast, including the native community of Island of Jean Charles, which the Corps did not see fit to include inside the Morganza to the Gulf.

For communities that benefit from dike protection, the problem is that dikes are a classic definition of what economists call a perverse incentive – instead of reducing the risk of flooding, they often increase it by incentivizing. more people to live in these areas. If a city arises next to a flood-prone river and the local government builds a dike along the river, more people will move to the city because they believe the dike protects them from flooding.

Horowitz sees the risk of a dike failure like that which occurred in the parish of Plaquemines as part of life on an unpredictable planet. Living in the shadow of a dike is rational, he says, for the same reason getting on an airplane is rational: there is some risk in doing anything or living anywhere.

“Would you like to cross a river?” There are only a number of ways to do it, ”he told me. “You can go to a bridge you hope you won’t fall, a boat you hope won’t sink, a helicopter you hope won’t crash – at some point you have to cross the water.”

But there is a permanent way to escape the kind of fate that has befallen the people of Lafitte: to get out of the way completely, which, according to Horowitz’s metaphor, would be tantamount to staying on dry land and refuse to cross the river. This type of coordinated relocation is known among climate experts as “managed retirement”, And it is gaining more and more importance among climate experts as disasters become more expensive.

“As sea levels rise, more and more cities are going to ask us to spend all kinds of federal money on dike systems,” says Orrin Pilkey, retired coastal geographer at Duke, known as the father. managed retirement studies. Pilkey was body critic for decades. “It just seems silly to me to keep building rather than responding more flexibly – and in some cases that means moving,” Pilkey said.

Pilkey acknowledges that it is not possible to relocate to a big city like New Orleans, but he insists that in other places retirement is the only right solution. Unless you encourage people to move away from risky areas, he says, they will continue to lose their homes to floods and fires. The government has already started implementing such resettlement policies in cities like Houston, where it has purchased thousands of flood prone houses so residents can move to higher land nearby and areas like Coastal alaska, where several indigenous communities have moved completely away from the collapsing shores.

These policies are controversial by their very nature, as they run counter to people’s attachment to their home and the need for policies to encourage growth. The alternative, however, is to rely on structures like the ones that protect the canals digging a little deeper, and hope that the system will work next time, knowing that one day it will not work.

“I’m afraid their time is coming,” Pilkey says of New Orleans. It just wasn’t this time.

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