On August 29, 2005, Hurricane Katrina drowned New Orleans and notably the city’s low-income Lower Ninth Ward. The flooding killed almost 1,400 people. The levees and floodwalls, primarily built by the U.S. Army Corps of Engineers, failed to hold back the hurricane’s storm surge of seawater. Just a few days after the storm raged, President George W. Bush said, “I don’t think anybody anticipated the breach of the levees,” as media outlets showed survivors stranded on highway overpasses or stuffed into the city’s Superdome in putrid conditions.
But in 2001, just four years before the hurricane, scientists and engineers across Louisiana had predicted exactly what would unfold. They had shown how storm surge would swell and overwhelm the city’s inadequate defenses. I was with these scientists at the time and explained their predictions in a Scientific American article, but governments took almost no action on the improvements the scientists recommended.
In true American fashion, the U.S. ignored a solvable problem until disaster struck.
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Immediately after the catastrophe, politicians at all levels made grand statements about what needed to be done to better protect the city and coast. Two months after the tragedy I went back to battered southeastern Louisiana to see what the scientists, engineers and urban planners thought instead. In early 2006 Scientific American published an article mapping out three possible scenarios. Louisiana later issued its Coastal Master Plan (CMP) to put a host of improvements in place, which aligned with some of what I had reported, including, for example, a ring of upgraded defenses right around the city.
Since then state officials have updated the plan, most recently in 2023, and they are working on the next iteration for 2029. The question today is whether New Orleans is better protected against hurricanes than it was 20 years ago. The short answer is that the city itself has greater defenses—for now. Levees have been raised, floodwalls have been rebuilt using much sturdier designs, and enormous gates have been built to stop at least some sea surge from ramming directly into the city when a storm is approaching.
But outside the city, some places may not be safer. Others may even have to be abandoned. The vast marshland south, west and east of the city provides natural protection against deadly storm surges, but it is deteriorating, and as that continues, New Orleans will be more directly exposed to angry seas. Yet in July Louisiana officials canceled a keystone project that would have helped restore those wetlands.
All of the time, effort and money that has gone into protecting the state’s most populous city could now be at risk.
New Orleans lies in a bowl that is almost all below sea level. The land has been sinking for decades and continues to drop. The enormous Lake Pontchartrain, at sea level, looms on its northern side. The Mississippi River, also at sea level, runs along the city’s western and southern side, then turns south through many square miles of marshlands and empties into the Gulf of Mexico. Like many big rivers, the Mississippi floods during the spring and occasionally at other times. In southeastern Louisiana, the floods used to spill over natural banks and bring sediment, freshwater and nutrients to the wetlands—resources that keep plants thriving, counteract natural subsidence, and replace sediment that routine wave action and storms tend to scour away.
But people don’t see floods for the good they provide, just the homes they destroy and the humans they wash away. Louisiana’s municipalities and the corps built floodwalls along the many navigation channels that crisscross the city to keep water out of neighborhoods and commercial districts that lie below in the bowl. And for a century, the corps built levees—high, long mounds of earth, concrete and rock—along the entire length of the Mississippi, on both banks, north and south of New Orleans. Floods into the city stopped, but the lack of floods starved the wetlands of their lifeline. The thick mesh of plants began to die. The deterioration is so bad that the region is losing an acre of land—the size of a football field—every 100 minutes.
Of course it’s not possible now to remove sections of levees and walls because floods would ruin the municipal and industrial complexes humans have built there. The extensive network of canals and pumps that each day send simple rainwater and groundwater that collects in the bowl out to the lake could never keep up. In June the SwissRe Institute, which analyzes the insurance industry, reported that a repeat of Hurricane Katrina today would cost the industry nearly $100 billion—even though the city’s population remains 20 percent below what it was in 2005, when people fled or later moved away.
Since the CMP was first issued, New Orleans and the state have spent $14 billion to improve storm protection. They have built storm surge barriers and floodgates along the city’s perimeter to hold back high ocean water. They have raised levees that were too low to stop surges from big storms, armored levees that were soft, added more water pumping capacity and filled gaps between sections of levees that surround the city and immediate outlying areas. “There were a lot of gaps that were completed” in the Hurricane and Storm Damage Risk Reduction System, also known simply as the ring system, says Bradley Barth, operations chief at the state’s Coastal Protection and Restoration Authority.
The state has also broadened barrier islands, a line of long, thin, low islands in the gulf that rim the southern edges of the wetlands. Like speed bumps, barrier islands can cut down storm surges that are coming from the gulf and heading toward land, but they also can be worn away by those storms and regular wave action.
Beefier barrier islands, and a stronger ring around the city, mean New Orleans should fare better during large storms. Indeed, state officials say the defenses held well against Hurricane Isaac in 2012 and Hurricane Ida in 2021. “The system performed as expected,” Barth says.
Yet scientists and engineers are concerned that the extensive wetlands between the city’s perimeter and the coast’s edge, which continue to disintegrate badly, will allow future storm surges to march in unimpeded. The rule of thumb is that every four miles of healthy marsh can absorb enough water to knock down a storm surge by one foot. The surge during Katrina peaked at 25 to 28 feet in certain places.
The primary way to restore wetlands, in the CMP and other analyses, it to build what are known as diversions. River flooding supplies sediment that raises the wetland floor. The floods also provide freshwater, which lowers the salinity of saltwater that naturally washes in, keeping the many plants knit in a soggy but robust fabric that resists erosion. A diversion is a short opening that is cut in the levee. Cuts would be made along the south side of the Mississippi River, which faces the wetlands that extend to the open gulf. Gates would be installed across the cuts so that most of the year, the river would run as normal. But during the spring or other times of high water, engineers would open the gates and let the sediment-rich freshwater flow into the wetlands, providing vital sustenance. The CMP identifies numerous desired diversions.
In July, however, the state canceled the largest project, known as the Mid-Barataria Sediment Diversion, even though scientists had studied the plan for years, models and designs were completed, permits were granted and construction had begun. The work was also generally funded from the Deepwater Horizon Oil Spill Trust that oil and gas giant BP had established to settle claims for damages when the Deepwater Horizon oil rig exploded off the Louisiana coast in 2010, creating the largest marine oil spill in U.S. history.
“They had started construction back in August 2023, then the state just halted it,” says Alisha Renfro, a senior manager at the National Wildlife Federation, who has studied coastal Louisiana for 20 years. The organization advocates for coastal restoration and tries to make sure the latest science is used in any plans. The mid-Barataria cancelation “comes as a real disappointment,” Renfro says. “It was a long-term, large-scale solution to restoring coastal wetlands.”
Restoration groups such as Restore the Mississippi River Delta roundly criticized the decision as a politically motivated money grab. But Gordon Dove, who in 2024 was appointed by Governor Jeff Landry as chair of the state’s Coastal Protection and Restoration Authority, defended the decision. Writing in an August 15, 2025, guest column in the Times Picayune, Dove said the decision was made by the Landry administration, the U.S. Army Corps of Engineers and the Trustee Implementation Group to terminate the project because it “aimed to address coastal erosion in a limited area” and because initial cost estimates had been rising significantly and could detract from other restoration efforts. Barth told me the authority would “look to repurpose the money to shoreline protection and smaller diversions.”
Renfro says the move is confounding and that it feels like a throwback to the days immediately after Hurricane Katrina, when competing self-interests were arguing over what to do and fund. The state, she says, is stepping away from coordinated work and slipping back into “random acts of restoration” that would provide poorer protection overall.
No matter what officials do, New Orleans will continue to sink. The sea level will continue to rise. Climate change will continue to make storms stronger and rainfall heavier. Despite stouter levees, floodwalls and barrier islands, vibrant wetlands are crucial to long-term security, and the 2023 CMP relies on them. But 20 years after disaster, perhaps the harsh lessons of Katrina are fading and politics are resurging. As this year’s hurricane season plays out, Louisiana must remember the power of water. It must remember the damage Katrina caused, the lives it took and the cost of rebuilding, which is still going on. Above all else, Louisiana’s power brokers must listen to science. The cost of not doing so is all around them.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.