Study: Some parts of New Orleans' flood walls sinking nearly 2 inches per year

Yahoo

16 hours ago

New Orleans — As the Atlantic hurricane season has gotten underway, a new study published Friday by researchers at Tulane University reveals hotspots in New Orleans' concrete flood walls which had been strengthened in the aftermath of Hurricane Katrina.
The study found that the city's concrete flood walls are sinking faster than sea levels are rising, reducing capacity to block storm surges in some neighborhoods.
"There is certainly a potential in the future, if these rates continue, to degrade our level of protection of the flood protection system," Tulane professor Mead Allison, a co-author on the study, told CBS News.
This summer marks 20 years since Katrina made landfall on the Gulf Coast, leaving more than 1,300 people dead and displacing more than a million people across the region.
Following the destructive storm, $15 billion was spent to reinforce a levy system designed to keep water out. New Orleans, much of which lies below sea level, relies on this elaborate system of levees, pumps and drainage canals.
The study, published in the journal Science Advances, used satellite radar data to track shifts in ground elevation across the Greater New Orleans area between 2002 and 2020. It found that while most of the city remains stable, some neighborhoods, wetlands, and even sections of the region's post-Katrina flood protection system are sinking by more than an inch per year — with some areas experiencing up to 47 millimeters, or nearly 2 inches, of elevation loss 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 — in a statement.
"These results are a wake-up call," Allison said. "We need ongoing monitoring and maintenance to ensure that our flood defenses don't lose their level of protection beneath us."
If trends continue, and infrastructure is left unchecked, the study found wetlands east of the city could transform marshes into open water within the next 10 years if trends continue — effectively eliminating critical storm surge buffers to the Louisiana coast.
The study also identified some potential causes of the sinking hotspots. It found pockets of land are sinking around industrial sites, the Louis Armstrong New Orleans International Airport, and newer residential developments — areas where soil compression and groundwater withdrawal are likely contributors.
Researchers said the findings also underscore a few potential solutions to better protect New Orleans and other coastal communities across the globe, including frequent upgrades to the flood protection system and satellite monitoring.
Some residents living in the Michoud neighborhood on the city's east side — one of the areas identified in the study as sinking more rapidly than others — are concerned that maintenance won't be prioritized. Michoud resident Synthia Viltus pointed out that potholes and other smaller infrastructure issues in her neighborhood have remained unresolved for months.
"I have zero faith in state federal leaders to keep the levies updated," Viltus said.
The study did find a positive — some areas where industrial activities had been halted had actually caused the land to lift back up.
The study's authors also hope their work will help guide other coastal cities who may be facing similar challenges to New Orleans.
"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 in the statement. "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."
Ricky Boyett, spokesperson for the U.S. Army Corps of Engineers in New Orleans, said the urgent levee systems in the city were designed and built to withstand projected levels of land sinking until 2057.
"Every levee system in South Louisiana is subject to settlement, subsidence and sea level rise," Boyett said in a statement. "As a result, periodic levee lifts are required to maintain the established level of risk reduction, whether that be the New Orleans Hurricane system, Mississippi River levees or other systems in the region."
The USACE says it's already planning a major upgrade overhaul to the infrastructure so it can withstand a half-century of time passing — and the expected changes in elevation that may unfold throughout those years — until 2073.
Meanwhile, the Tulane researchers say they were commissioned to conduct this study by the state, which manages the levees. They say this study was only the first phase of a two-part series. Phase two will use the same technology to examine wetland sinkage along the southernmost areas of Louisiana's coast — the first line of defense to protect against a hurricane's surge.
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