New Orleans wetlands and floodwalls potentially sinking

JohannaSci/Tech2025-07-085900

NEW ORLEANS (WGNO) — A study published in the journal Science Advances found some parts of New Orleans may be sinking, though most of the city is remaining level.

Simone Fiaschi, an Earth Scientist and one of the study’s authors, said the research used satellite interferometric synthetic aperture radar, or InSAR. It is a technology used to analyze images collected from satellites. It studied vertical land motion, which is the movement of the surface of the ground up or down.

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By comparing differences between images collected over a long time span it can calculate vertical land motion. It utilized data from 2002-2020. The research itself began in 2020.

The study said that the wetlands outside of New Orleans may be experiencing a loss of 30 to 47 millimeters each year. Fiaschi said the wetlands could disappear, although he noted there is a range of uncertainty in the study.

“These rates are critical if you consider that of course the level, the elevation of the wetlands is basically at sea level, so if these rates continue as they are it’s possible in the next few years the wetlands could disappear because it would become open water,” Fiaschi said.

Ricky Boyett, a spokesperson for the Army Corp of Engineers, said they have to mitigate the effects of any building they oversee that impacts the wetlands.

“Wetlands have a huge role, not only do they have a huge role in water quality, life with regards to the different species of animals and fish and plants that depend on it, they also have a flood risk management component to it. So, wetlands are indispensable when it comes to south Louisiana,” Boyett said.

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According to the study, portions of the flood protection walls constructed after Hurricane Katrina may be experiencing a decrease in elevation of up to 28 millimeters per year. However, Fiaschi said the exact rates may not be correct because they were unable to validate the results with ground information.

“If the rates are true and real that may affect the protection that the floodwalls are bringing against the storms and hurricanes in the future because we are losing ground and the height of the floodwalls is also going down,” Fiaschi said.

Boyett said elevation loss on the levees due to subsidence is a regular aspect of building in New Orleans.

Boyett said that adding weight to the ground in the form of levees will increase subsidence and compaction. He said relative sea-level rise can also play a factor, as the land is sinking and the water is coming up. It is something they always have to keep in mind in building the flood protection system.

“It’s always known that your levees are going to subside here, one person described it as we’re building these massive mounds of dirt on the equivalent of pudding, so it’s going to sink,” Boyett said.

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