Groundwater usage increasing city’s subsidence, according to NASA study
21st June 2016 · 0 Comments
By Mason Harrison
Contributing Writer
New Orleans is a city with many nicknames, among them, “the greatest sinking city in the world.” This month, a new federal report gives light to just how great the city’s subsidence has become as New Orleans battles ever-present sinkholes damaging its roadways.
Described as the most expansive examination of the city’s subsidence to date, the study is produced by the NASA space agency, researchers from the University of California at Los Angeles and from the Center for GeoInformatics at Louisiana State University.
Studies of subsidence in New Orleans date back as far as 1955, when researchers from the oceanic and atmospheric administration conducted surveys of the Michoud region.
Five decades later the Michoud area continues to be a region of concern as it sinks up to two inches each year, with the Upper and Lower Ninth wards also under threat. The Bonne Carre Spillway shows a troubling rate of up to 1.6 inches of sinking each year.
The city’s subsidence is linked to natural geologic factors, but also human activity, the removal of groundwater, oil and natural gas from under the soil causing the earth to fall. Dr. Cathleen Jones, who led the research study for NASA, says constant removal of groundwater causes soil to collapse, compact and prevent new water from replenishing the soil.
Jones says the rate of subsidence in southeast Louisiana is “slightly faster” than in years past as shown through the agency’s aircraft equipped with special radar for the project. The new study is more “spatially localized,” says Jones, allowing the agency to pinpoint subsidence in areas like Metairie, Norco and in significance, portions of Harahan.
Mark Heck, president of the Bywater Neighborhood Association, describes the data as “scary” and simply confirms “something that we have known for years.” Heck, however, says while subsidence is concerning, “there are so many other things to care about.”
For years, residents of New Orleans and the surrounding suburbs have been bombarded with messages about a subsiding earth and the loss of a “football field an hour” of marshland, leading to a din of statistics that cause residents to tune out the research.
But CBD resident Steven Kennedy sees the report in a different light. “The NASA study shouldn’t be taken lightly at all. It shows that not only do we have to worry about coastal erosion we also as a city must understand and implement some of the suggestions from the Greater New Orleans Urban Water Plan,” says Kennedy, an urban planner.
The urban water plan, a product of Greater New Orleans, Inc., describes drainage systems as the “primary cause of subsidence in the region.” The city’s drainage system, according to the GNO, Inc. report, “has developed into a destructive cycle in which pumping and low water levels cause the land to sink, which then necessitates increased pumping capacity in order to keep dry, which then leads to further subsidence,” costing billions.
Overall subsidence in greater New Orleans averages 0.31 inches each year, but locally, according to the report, “Michoud shows the most subsidence (typically .05-1.1 inches), with the next highest subsidence occurring in the vicinity of the Upper 9th Ward and eastward in the area between the Mississippi River and Bayou Bienvenue (typically 0.3-0.7 inches).…
Subsidence of smaller magnitude, but statistically significant, occurs in eastern Metairie (0.1-0.5 inches) and at some locations along the Mississippi River, particularly in Jefferson Parish. A subsiding area often shows up on both banks of the river; e.g., the area on the west bank opposite Chalmette shows higher subsidence than nearby areas…”
The solutions outlined in the urban water plan rest on adapting how New Orleans deals with rainwater. “The current approach,” according to the report, “to managing stormwater says that every drop of water that falls must be pumped out. This leads to water and soil imbalances. Intelligent retrofits and a new approach to stormwater and groundwater management will provide measurably higher levels of safety, reduce the rates at which the region is sinking…” But efforts to implement and fund the plan have stalled.
New Orleans Mayor Mitch Landrieu has urged state leaders to address rising sea levels, which is not a direct threat to the city’s elevation, but becomes a more substantial problem as the city continues to subside and the water surrounding it rises over the horizon.
City officials charged with infrastructure improvements to combat subsidence continue to develop plans to mitigate the longstanding problem, but further details from the public works department and the Sewerage and Water Board were not available at press time.
“Subsidence is a major concern for us all because of its impact on infrastructure, but also on our homes and businesses. Often we notice little cracks in the walls of our homes, yet there are times when we don’t realize the ground is shifting until it is often too late.”
This article originally published in the June 20, 2016 print edition of The Louisiana Weekly newspaper.
