Ten years ago this week Hurricane Katrina drowned New Orleans. The long, high, earthen levees and concrete floodwalls that were meant to protect neighborhoods inside and outside the city washed away, even though they were supposed to be able to withstand a category 3 hurricane like Katrina. More than 1,800 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 time, the state of Louisiana, federal agencies, huge engineering 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 city toward the Gulf of Mexico, to improve protection against big storms. The studies agreed on certain basic solutions and disagreed on others, but the recommended work barely began because 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.

It took state officials, scientists and engineers seven years to finally agree on a master recovery plan, released in 2012, and only then did work begin in earnest. The region had dodged an annual bullet because no big hurricane had returned. But several shortcomings in the plan, being discussed by experts, raise questions about whether the New Orleans area is safer now and whether it will be safer in the future.

Safer Inside the city
Experts agree that flood protection is now better inside the city, which is essentially ringed by tall levees along the Mississippi River on the south side and along big Lake Pontchartrain on the north side (see map below).

The levees had originally been designed to withstand a category 3 storm but some sections were never built to that full height and others were just poorly constructed, according to various studies. Making matters worse, the levees sank over time, because the entire region is subsiding. Many levees whose slopes were lined with grass were also weakened by waves brought in by the surge, which tore away the soft surface. The Corps has now raised the levees back to full height and finished the sections that were never high enough. It has also “hardened” the slopes of many levees with heavy rock or concrete to withstand waves.

Levees do not fully protect the city from encroaching seawater, however. It can flow in along the numerous channels that allow ships to navigate and spill into the drainage canals that catch rainwater and storm runoff and pump it out of downtown. As 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 not hold. The Corps has replaced them with walls shaped like an upside-down “T” that are known to be stronger.

The city also made a dramatic move and cut off a large navigation channel known as the MRGO, which for years had allowed 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 path and levees along MRGO and another navigation channel created a funnel effect that built the surge up even higher, helping it pour into the interior channels. The Corps has built an enormous floodgate across the entire funnel area, 2.9 kilometers long and eight meters high. It stays open to let water and ships through but 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 city 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 improve education, housing, health care and other social priorities. Gregory Baecher, a civil engineering professor at the University of Maryland, College 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 will have to be continually raised as 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 strength goes up to 5) could overrun the improved protection.

Furthermore, that design criteria misses a bigger point, Baecher says. The Saffir–Simpson scale is based on a storm’s sustained wind speed, but for coastal cities, the much bigger threat is not high wind but storm 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 design criteria to the one most engineering and risk-analysis firms use for surges: the so-called 100-year storm, an event rare enough that it would only happen once a century. This is often translated as a 1 percent chance that a storm of that power would hit in a given year.

Yet that is insufficient, in Baecher’s opinion. “The 100-year storm criterion came from the National Flood Insurance Act of 1968, and it was designed to protect real estate, not human lives,” he explains. “No one thinks a 1 percent threshold is adequate for protecting life. Most engineers, Baecher maintains, “would say a 500-year storm is more appropriate—and that surge might be 10 meters higher than a 100-year storm.” Long-term, Baecher says, New Orleans and other coastal cities should plan for 500-year storm surges, because rising sea level makes them more and more likely. Indeed, some estimates say that by 2070 or 2080, a one-in-100-year storm like Katrina or Hurricane Sandy that hit the New York–New Jersey region could return once every two to three years.

Many projects (noted in the key) would be needed to rebuild vast but tattered wetlands (brown area) that would help protect New Orleans (center, near top) from surges of floodwater driven in by hurricanes. Chief among them are sediment diversions (brown circles)—cuts in levees along the Mississippi River (winding white line), with gates that would open to allow nourishing sediment and freshwater to flow into the wetlands, revitalizing them. A 2.9-kilometer wall with gates to block surges from entering inner-city navigation channels has also been built (orange triangle just under the label “New Orleans East”).
Credit: Detail of a map from Louisiana’s Comprehensive Master Plan for a Sustainable Coast. Coastal Protection and Restoration Authority of Louisiana. Baton Rouge, LA. 2012.

More dangerous outside the city
Of course it is good news that New Orleanians living inside the city are safer, at least for a while. But outside the city walls, the danger from storm 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 two million people live across the wider delta region—all of it threatened by storms. Fixing this much larger area is crucial and far behind. And in the long-term, it is the key to protecting the city itself.

The wetlands across the delta were once vast and thick. In that condition, they can absorb some of a storm’s surge, and to an extent they can grow as sea level rises, helping to keep high water at bay. They have disintegrated because of the many navigation channels as well 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, because the Corps built continuous levees along the entire length of the lower Mississippi River, which passes the city and continues another 112.5 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 also prevents pure ocean water from intruding further inland, which kills grasses and trees.

The state’s 2012 plan, Louisiana’s Comprehensive Master Plan 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. But there simply is not enough sediment in the Mississippi River to do that, according to the state’s plan itself as well as plans released last week as part of a large, international reengineering and redesign competition called Changing Course. If the cuts, known as diversions, are to succeed in rebuilding some wetlands, then other wetlands—and the communities in them—will have to be left out. In the design competition, three independent groups concluded that wetlands closer to the city 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 be a sustainable delta, but it will be smaller,” says Steve Cochran, director for Mississippi River Delta Restoration at the Environmental Defense Fund, who oversaw the competition.

“There are areas we are not going to be able to restore” to their former condition, acknowledges Jimmy Frederick, spokesperson for the Coalition to Restore Coastal Louisiana. “Those are the hard choices. Our next governor [to be elected this October] is going to have to make those decisions.”

In the meantime little work has been done and it has brought only a small amount of wetland back. The marshes are disappearing fast—a football 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 against the sea.

Because politicians and government agencies are loath to say that certain communities must basically be abandoned, the state master plan only softly acknowledges this potential fate. The three winning designs of the Changing Course competition state it more directly. And Baecher says it most forcefully of all. “Restoring the whole delta is a fairy tale,” he says. “We can only slow down the destruction.”

BP settlement is not enough
One impediment to more wide-scale work, of course, is money. The levee, floodwall and gate work in the city as well as other projects such as larger pumps to evacuate water, cost more than $14 billion. But the state’s entire plan of more than 100 recommended projects to revitalize the delta region is estimated to cost a separate $50 billion.

Only a small amount of that work has been funded, in part because the state and federal government had been waiting for a tar-stained golden goose: penalty money from the 2010 BP Deepwater Horizon oil spill in the Gulf. In July a global settlement was finally announced. Louisiana would get $6.8 million of the $18.7 billion, with $5.8 billion earmarked for restoration. Criminal settlements could push the state’s take to $8 billion, according to various estimates.  

Those funds are a good start. But “there is not enough money just from the BP settlement,” Landrieu said at the National Press Club on August 18. “We will need money from the oil industry.” The oil companies, he explained, “helped break New Orleans, they should help fix it. They can drill, but then they have to restore.” He also noted that if the industry does not put money back into the wetlands, “their own infrastructure will deteriorate.”

Industry money will not be enough, either. “In reality, the $50-billion plan will probably be a $100-billion plan with inflation over many years,” Frederick says. “There will have to be government money—taxpayer money.”

Social concerns need solving, too
Physically protecting New Orleans will not make it a resilient city. Without better schools, affordable housing and more jobs, New Orleans will degrade socially and economically and people will leave. Making the city sustainable is Landrieu’s bigger goal.  The Resilient New Orleans strategy he revealed on August 25 was created over the past two years with leaders from federal agencies and an organization called 100 Resilient Cities, backed by the Rockefeller Foundation. It stresses that physical and social improvements must be integrated. “The storm didn’t create all of our problems,” Landrieu said at the unveiling. “When communities are strong, when there is equity, then we can withstand whatever comes our way.”

New Orleans is a great American comeback story in the making, he said, “ but we have to get stronger.” He sees recovery work as one avenue, noting that “52 percent 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 system.

A leader in the 100 Resilient Cities network, Landrieu also sounded the charge for them. “New Orleans is a canary in the coal mine” for cities worldwide that must adapt to rising sea levels and stronger storms, he said. Indeed, last week RMS, the international catastrophe risk management firm, stated that other U.S. coastal cities are more at risk to storm surges than New Orleans. Tampa has a one-in-80 annual chance that a hurricane would cause flood losses of at least $15 billion. Miami has a one-in-125 chance, New York one-in-200, and New Orleans one-in-440. 

Part 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 water out. Now it means better ways to manage water when it comes in, which it will inevitably do. “We cannot stop bad things from coming our way,” Landrieu said. “But we can be better prepared.”