Ten years agone this week Hurricane Katrina drowned New Orleans. The long, high, earthen levees and concrete floodwalls that were meant to protect neighborhoods within and outside the metropolis done abroad, even though they were supposed to be able to withstand a category 3 hurricane like Katrina. More than one,800 people died. Damages surpassed $100 billion.

After the tragedy the U.S. Army Corps of Engineers, which had built most of the levees and floodwalls, began an extensive campaign to repair them. At the same fourth dimension, the state of Louisiana, federal agencies, huge technology companies and the Corps conducted major studies about how to redesign New Orleans and rebuild the vast but crumbling Mississippi River delta wetlands extending from the metropolis toward the Gulf of Mexico, to ameliorate protection against big storms. The studies agreed on certain basic solutions and disagreed on others, but the recommended piece of work barely began considering of political infighting and lack of funding. Demolished neighborhoods such as the Lower 9th Ward rotted. Tattered marshes disintegrated. Disgusted, more than 100,000 residents who lost their homes or jobs left the city permanently.

Information technology took land officials, scientists and engineers seven years to finally agree on a master recovery program, released in 2012, and only then did piece of work begin in earnest. The region had dodged an annual bullet because no large hurricane had returned. Only several shortcomings in the programme, being discussed by experts, heighten questions about whether the New Orleans surface area is safer now and whether it will be safer in the hereafter.

Safer Within the city
Experts concord that inundation protection is now amend within the city, which is essentially ringed past alpine levees along the Mississippi River on the south side and forth big Lake Pontchartrain on the north side (see map beneath).

The levees had originally been designed to withstand a category iii tempest just some sections were never congenital to that full pinnacle and others were but poorly constructed, according to diverse studies. Making matters worse, the levees sank over time, considering the entire region is subsiding. Many levees whose slopes were lined with grass were too weakened by waves brought in by the surge, which tore away the soft surface. The Corps has at present raised the levees dorsum to full height and finished the sections that were never high enough. Information technology has also "hardened" the slopes of many levees with heavy stone or concrete to withstand waves.

Levees do not fully protect the urban center from encroaching seawater, however. It can menstruum in forth the numerous channels that permit ships to navigate and spill into the drainage canals that catch rainwater and storm runoff and pump it out of downtown. Every bit the surge from Katrina poured into these waterways it toppled the floodwalls, drowning the city from the inside out. Many of them were "I"-shaped and their bases did non hold. The Corps has replaced them with walls shaped like an upside-down "T" that are known to exist stronger.

The city also made a dramatic motion and cut off a large navigation channel known as the MRGO, which for years had immune salty seawater to seep deep into the wetlands east of New Orleans, killing the marshy grasses, mangroves and trees from the roots up. Over decades, thick marshes became nearly open water, allowing the sea to stream in. When the storm surge came, the open up path and levees along MRGO and another navigation aqueduct created a funnel upshot that built the surge upwards fifty-fifty higher, helping it pour into the interior channels. The Corps has built an enormous floodgate beyond the entire funnel surface area, 2.9 kilometers long and eight meters loftier. It stays open to let water and ships through only can be closed when a storm approaches, and it functioned well when Hurricane Isaac, a category 1 storm, made landfall nearby in August 2012.

Overall, "the urban center is much safer than it was," said Mitch Landrieu, mayor of New Orleans, at the August 25 unveiling of the Resilient New Orleans strategy, a blueprint for integrating rebuilding efforts with programs to better didactics, housing, health care and other social priorities. Gregory Baecher, a civil technology professor at the University of Maryland, Higher Park, who has overseen some of the biggest studies on how to reengineer southeastern Louisiana, agrees. "Is New Orleans safe than before Katrina? Yes."

Baecher points out, however, that the improved protection measures will need ongoing upgrades. Sinking levees volition accept to exist continually raised every bit the city subsides further and as sea level continues to rise. And of course, a storm larger than category 3 (the Saffir–Simpson scale that is used to rate hurricane forcefulness goes up to 5) could overrun the improved protection.

Furthermore, that pattern criteria misses a bigger bespeak, Baecher says. The Saffir–Simpson scale is based on a storm's sustained wind speed, merely for coastal cities, the much bigger threat is non loftier wind but tempest surge, and there's no scale to measure that. Steps to retrofit New Orleans should be driven by surge heights. The Corps has changed its pattern criteria to the 1 near engineering and risk-assay firms use for surges: the so-chosen 100-twelvemonth tempest, an event rare plenty that it would simply happen once a century. This is oftentimes translated equally a 1 percent hazard that a storm of that ability would hitting in a given year.

Yet that is bereft, in Baecher's opinion. "The 100-twelvemonth storm benchmark came from the National Inundation Insurance Act of 1968, and it was designed to protect real estate, not human lives," he explains. "No one thinks a ane pct threshold is adequate for protecting life. Most engineers, Baecher maintains, "would say a 500-year storm is more than appropriate—and that surge might be x meters higher than a 100-yr storm." Long-term, Baecher says, New Orleans and other coastal cities should programme for 500-year tempest surges, because rising sea level makes them more and more likely. Indeed, some estimates say that by 2070 or 2080, a ane-in-100-year storm like Katrina or Hurricane Sandy that hit the New York–New Bailiwick of jersey region could return once every ii to three years.

Many projects (noted in the cardinal) would be needed to rebuild vast but tattered wetlands (brown expanse) that would help protect New Orleans (eye, most peak) from surges of floodwater driven in by hurricanes. Chief amongst them are sediment diversions (dark-brown circles)—cuts in levees along the Mississippi River (winding white line), with gates that would open to let nourishing sediment and freshwater to flow into the wetlands, revitalizing them. A 2.9-kilometer wall with gates to block surges from entering inner-metropolis navigation channels has also been built (orangish triangle just under the label "New Orleans Due east").
Credit: Detail of a map fromLouisiana's Comprehensive Master Plan for a Sustainable Coast. Coastal Protection and Restoration Say-so of Louisiana. Baton Rouge, LA. 2012.

More dangerous exterior the city
Of course information technology is practiced news that New Orleanians living inside the city are safer, at to the lowest degree for a while. Simply outside the city walls, the danger from tempest surge is greater than ever.

Today, about 385,000 people live in the city proper, in addition to another 800,000 who reside in the immediate metro area. More than 2 million people live across the wider delta region—all of it threatened by storms. Fixing this much larger area is crucial and far backside. And in the long-term, it is the key to protecting the city itself.

The wetlands beyond the delta were once vast and thick. In that status, they can absorb some of a storm's surge, and to an extent they tin can grow as sea level rises, helping to go along high water at bay. They accept disintegrated considering of the many navigation channels likewise as hundreds of kilometers of smaller channels cut by the oil and gas industry to build and maintain pipelines running in from the Gulf of Mexico. The wetlands cannot repair themselves, however, considering the Corps built continuous levees along the entire length of the lower Mississippi River, which passes the urban center and continues another 112.five serpentine kilometers until it reaches the Gulf. The levees prevented regular floods from harming farms, industries and towns along the river's course. But the lack of annual floods starved the marshes of large quantities of nourishing silt and freshwater. The freshwater too prevents pure ocean water from intruding further inland, which kills grasses and copse.

The state's 2012 program, Louisiana'due south Comprehensive Principal Program for a Sustainable Coast, concluded that the best way to renew the natural processes that sustain the marshes is to make cuts in the levees, install gates and open those gates periodically to allow sediment and freshwater to once again flow in. Independent studies agreed.

The stated goal was to try to "restore" the wetlands to their former rich, vast condition. Merely there simply is not enough sediment in the Mississippi River to exercise that, according to the state's plan itself equally well as plans released last week as part of a large, international reengineering and redesign competition chosen Changing Form. If the cuts, known as diversions, are to succeed in rebuilding some wetlands, then other wetlands—and the communities in them—volition have to be left out. In the design competition, three independent groups concluded that wetlands closer to the metropolis could be saved if all the sediment were used there, which would leave out areas at the far ends of the delta. The groups agreed "there can exist a sustainable delta, but information technology will be smaller," says Steve Cochran, manager for Mississippi River Delta Restoration at the Environmental Defense Fund, who oversaw the competition.

"There are areas we are not going to exist able to restore" to their onetime condition, acknowledges Jimmy Frederick, spokesperson for the Coalition to Restore Coastal Louisiana. "Those are the hard choices. Our adjacent governor [to be elected this October] is going to take to make those decisions."

In the meantime footling work has been washed and it has brought only a small amount of wetland dorsum. The marshes are disappearing fast—a football game field's worth is lost every hour. Without them the communities outside New Orleans will be even more vulnerable to storm surges, and ultimately, the city itself will lay naked confronting the sea.

Because politicians and regime agencies are loath to say that certain communities must basically be abandoned, the state principal plan only softly acknowledges this potential fate. The three winning designs of the Changing Grade competition state information technology more than directly. And Baecher says it nearly forcefully of all. "Restoring the whole delta is a fairy tale," he says. "We can only slow down the devastation."

BP settlement is non plenty
One impediment to more than wide-calibration work, of course, is money. The levee, floodwall and gate work in the urban center as well as other projects such as larger pumps to evacuate water, price more than than $fourteen billion. Merely the land's entire program of more than 100 recommended projects to revitalize the delta region is estimated to cost a dissever $50 billion.

Only a small amount of that piece of work has been funded, in office because the state and federal government had been waiting for a tar-stained golden goose: punishment money from the 2010 BP Deepwater Horizon oil spill in the Gulf. In July a global settlement was finally announced. Louisiana would become $6.8 million of the $18.vii billion, with $five.8 billion earmarked for restoration. Criminal settlements could push the state'southward take to $8 billion, according to various estimates.

Those funds are a expert offset. Only "there is not enough coin just from the BP settlement," Landrieu said at the National Press Club on August xviii. "Nosotros will need money from the oil manufacture." The oil companies, he explained, "helped suspension New Orleans, they should help set up it. They can drill, but then they have to restore." He also noted that if the industry does not put coin dorsum into the wetlands, "their own infrastructure will deteriorate."

Industry money will not be enough, either. "In reality, the $50-billion plan will probably exist a $100-billion plan with inflation over many years," Frederick says. "In that location volition have to be government coin—taxpayer coin."

Social concerns demand solving, also
Physically protecting New Orleans will not get in a resilient urban center. Without better schools, affordable housing and more jobs, New Orleans will degrade socially and economically and people will leave. Making the urban center sustainable is Landrieu's bigger goal.  The Resilient New Orleans strategy he revealed on August 25 was created over the by two years with leaders from federal agencies and an organization chosen 100 Resilient Cities, backed by the Rockefeller Foundation. It stresses that physical and social improvements must exist integrated. "The tempest didn't create all of our problems," Landrieu said at the unveiling. "When communities are stiff, when at that place is equity, so we can withstand whatever comes our style."

New Orleans is a great American comeback story in the making, he said, " only nosotros have to get stronger." He sees recovery work as one avenue, noting that "52 percentage of the African-American men in the city are not working." A lot of them, he said, could be employed to build a new water management organisation.

A leader in the 100 Resilient Cities network, Landrieu likewise sounded the charge for them. "New Orleans is a canary in the coal mine" for cities worldwide that must adapt to rising body of water levels and stronger storms, he said. Indeed, last calendar week RMS, the international catastrophe take chances management business firm, stated that other U.S. coastal cities are more at risk to storm surges than New Orleans. Tampa has a 1-in-80 annual chance that a hurricane would cause overflowing losses of at least $fifteen billion. Miami has a i-in-125 chance, New York one-in-200, and New Orleans one-in-440.

Function of Landrieu's inspiration for all these cities is his new mantra for New Orleans: "living with water." That used to mean trying to keep h2o out. Now it means ameliorate ways to manage water when information technology comes in, which it will inevitably do. "We cannot terminate bad things from coming our way," Landrieu said. "But we can be better prepared."