When a city already sits below sea level, any additional sinking is cause for concern. This is especially true of New Orleans, a major U.S. port with the largest metropolitan area in the state of Louisiana.
Scientists have known for some time that New Orleans is sinking, but a new study has found that New Orleans and the surrounding metropolitan area is losing elevation at a faster rate than previously thought.
The sinking is a process called subsidence, and with the use of satellite mapping, it was found that different areas of the city are sinking at varying rates, some as much as two inches or more a year due to a combination of natural geologic and human-induced processes.
The new study, according to Phys.org, is a collaborative effort between scientists at NASA's Jet Propulsion Laboratory, Pasadena, California; UCLA; and the Center for GeoInformatics at Louisiana State University, Baton Rouge, took place from June 2009 to July 2012.
The study used newer NASA airborne radar imagery that produced higher resolution mapping that was more spatially extensive than older radar images. The mapping proved to be very telling, showing some areas of new Orleans, such as the Norco industrial area, Michoud, Metairie and the Upper and Lower 9th Ward were having the highest rates of subsidence.
The study cites a number of reasons for the increased subsidence, but the two primary reasons seem to be groundwater pumping and dewatering, a process where surface water is removed. This is used to lower the water table to prevent standing water in some areas.
Lead author Cathleen Jones, a JPL scientist, says the study will prove to be useful in helping planners to more effectively combat subsidence in the city, while "improving the long-term coastal resiliency and sustainability of New Orleans."
The maps were produced using NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), which uses a technique known as interferometric synthetic aperture radar (InSAR). The process can measure any deformations in land surface measurements with centimeter accuracy.
New Orleans is not the only spot in the world where subsidence is becoming a problem. The prolonged drought in California has resulted in the ground sinking in some areas due to groundwater reserves being pumped out. And along many coastlines around the world, delta areas are also sinking. A rise in sea levels (some three inches since 1992) is also a factor. "People need to understand that the planet is not only changing, it's changed," a NASA scientist says.
This study, "Anthropogenic and geologic influences on subsidence in the vicinity of New Orleans, Louisiana," was published in the Journal of Geophysical Research on May 16, 2016. (Digital Journal)
PHOTO: New Orleans is ringed by hundreds of miles of levees to protect against flooding.
CREDIT: Mario Tama, Getty/AFP/File.