Parts of Greater New Orleans are sinking at rates that researchers say could complicate long-term flood protection. A peer-reviewed study by NASA and Tulane University researchers, published in Science Advances, found that some neighborhoods, wetlands, and sections of floodwalls are sinking by more than 1 inch per year, with the worst hotspots losing nearly 2 inches annually. For a city where much of the land already sits below sea level, the authors say the uneven drop can affect residents, infrastructure planning, and the post-Hurricane Katrina flood protection system.
Radar Data Reveals Uneven Sinking
The study mapped vertical land motion across Greater New Orleans and found that subsidence is not uniform. Some areas are relatively stable, while others are dropping quickly enough that the authors warn it could affect levees and floodwalls over time. The research team documented localized subsidence rates reaching approximately 47 mm per year, or about 1.85 inches, in the most affected zones. That figure is roughly ten times faster than the long-term regional average recorded by federal surveys over the second half of the 20th century.
The spatial variation is the critical finding here, not just the peak rate. Uniform sinking would be more manageable because engineers could design for a single, predictable number. But when one stretch of a floodwall drops an inch while an adjacent section barely moves, the resulting stress and misalignment create weak points that standard maintenance schedules may not catch. The study’s high-resolution mapping makes those differences visible for the first time at a neighborhood-by-neighborhood scale, giving engineers and emergency managers a clearer picture of where to focus limited resources.
Where the Ground Is Falling Fastest
The steepest declines cluster around industrial corridors and flood-control structures. Earlier NASA radar work, conducted from June 2009 to July 2012 using the agency’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), had already flagged trouble in these areas. That campaign found sinking up to 2 inches (50 mm) per year in parts of the region. The highest rates appeared upriver along the Mississippi River around major industrial areas in Norco, where heavy infrastructure and altered wetlands sit atop soft delta sediments.
Just east of Norco lies the Bonnet Carre Spillway, which serves as a critical flood outlet when the Mississippi River runs high enough to threaten New Orleans’ levees. The earlier NASA study measured sinking of up to 1.6 inches (40 mm) per year behind and near the spillway. A flood barrier that is itself subsiding presents an obvious problem: its effective height shrinks each year, reducing the margin of safety it was designed to provide. The new Science Advances paper aligns with the earlier findings in highlighting continued uneven subsidence in the region, reinforcing concerns raised in the NASA reporting that protective elevations can change over time and may warrant closer monitoring.
Human Activity and Geology Working Together
Subsidence in the New Orleans region has two broad sets of drivers, and separating their contributions matters for deciding what can actually be fixed. A related study published in the Journal of Geophysical Research: Solid Earth and hosted through NASA’s sea level portal analyzed both anthropogenic and geologic influences on sinking around the city. Natural compaction of the Mississippi River delta’s young, water-rich sediments accounts for part of the decline. As those sediments slowly squeeze and dewater under their own weight, the land surface drops even without human interference…