New Orleans is slowly sinking — and in some spots, the drop is startling.
A Tulane University study using two decades of satellite radar data reveals parts of the city, its wetlands, and even billion-dollar post-Katrina floodwalls are losing up to two inches of elevation each year.
Sinking Threat to New Orleans and Its $15 Billion Flood Defenses
Parts of New Orleans and nearby wetlands are slowly sinking. While much of the city’s ground remains stable, new research from Tulane University indicates that some parts of the $15 billion flood protection system built after Hurricane Katrina may require ongoing upgrades to stay ahead of this gradual land loss.
Published in Science Advances, the study examined ground elevation changes across Greater New Orleans from 2002 to 2020 using satellite radar data. The analysis revealed that certain neighborhoods, wetlands, and even sections of floodwalls are sinking more than an inch each year, with some locations dropping as much as 47 millimeters (nearly 2 inches) annually.
“In a city like New Orleans, where much of the land is already near sea level, even minor drops in elevation can increase flood risk,” said Simone Fiaschi, lead author of the study and a former researcher with Tulane’s Department of River-Coastal Science and Engineering, now employed at TRE-Altamira.
Forces Driving the Land’s Descent
The research shows that a combination of natural and human activities is reshaping the city’s terrain. This sinking, called subsidence, is linked to natural soil compaction, groundwater extraction, industrial development, and the long-term effects of draining wetlands for urban growth.
To create the most detailed map yet of vertical land movement in New Orleans, the team used a remote sensing method known as InSAR (Interferometric Synthetic Aperture Radar). This technology measures tiny changes in surface elevation by comparing satellite radar images taken over time, providing data even for wetlands where past measurements were unreliable.
Floodwalls and Levees Losing Elevation
Among the most troubling findings: some of the concrete floodwalls and levees built to protect the city after Katrina are themselves sinking. In a few cases, parts of the Hurricane and Storm Damage Risk Reduction System (HSDRRS) are losing elevation faster than sea levels are rising, reducing their capacity to block storm surges.
“These results are a wake-up call,” said co-author Prof. Mead Allison, also of Tulane. “We need ongoing monitoring and maintenance to ensure that our flood defenses don’t lose their level of protection beneath us.”
Uneven Ground Movement Across the Region
The study also found pockets of sinking around industrial sites, the airport, and newer residential developments — areas where soil compression and groundwater withdrawal are likely contributors. In contrast, some areas, such as parts of Michoud, showed modest land uplift, likely due to the halt of industrial groundwater pumping and recovery of the water table.
Wetlands east of the city, long known for their ecological importance, are also sinking rapidly in places. In some spots, the loss of elevation could transform marshes into open water within a decade if trends continue. This has implications not just for wildlife but also for storm protection, as wetlands help buffer storm surges.
Rising Seas, Narrowing Margins of Safety
New Orleans, much of which lies below sea level, relies on an elaborate system of levees, pumps and drainage canals to keep water out. As sea levels rise and the ground sinks, the margin for error narrows.
Experts say that without sustained monitoring, including satellite data and ground-based measurements, it’s difficult to know where to reinforce levees or how to plan for future storms.
“This research shows that land movement isn’t uniform, and understanding these patterns is crucial for protecting lives and property in a city where inches truly matter,” Fiaschi said. “However, it’s crucial to remember that our results still require careful ground-truthing. This is especially true for critical areas like the floodwalls, where on-site verification was not possible during this project.”
Global Lessons in Coastal Resilience
The study highlights the potential of satellite monitoring to guide infrastructure maintenance and urban planning, not just in New Orleans but in coastal cities worldwide facing similar challenges.
Reference: “Vertical land motion in Greater New Orleans: Insights into underlying drivers and impact to flood protection infrastructure” by Simone Fiaschi, Mead A. Allison and Cathleen E. Jones, 27 June 2025, Science Advances.
DOI: 10.1126/sciadv.adt5046
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2 Comments
Our ancestors who founded NO can be forgiven for their ignorance about subsidence and their decision to build a city on a river delta. However, we not only know about subsidence, but we can measure and map the differential subsidence. It is folly — throwing bad money after good money — to try to keep patching a poor situation. It is evidence that humans are not really rational creatures. An emotional attachment to where one calls “home,” is not a good reason to keep spending money on predictable repairs.
Moving upriver would seem to be inevitable. Baton Rouge seems be better sited. Does it have the protential to be another Houston?