New Orleans and surrounding areas continue to sink at highly variable rates due to a combination of natural and human-induced processes, according to a new study by LSU, UCLA and NASA.
The study covered the period from June 2009 to July 2012. LSU says NASA airborne radar observed rates of sinking generally consistent with, but somewhat higher than, previous studies conducted using different radar data. The research was the most spatially extensive, high-resolution study to date of regional subsidence in and around New Orleans, measuring its effects and examining its causes, the university says.
The highest rates of sinking—at up to 2 inches per year—were observed upriver along the Mississippi River around major industrial areas in Norco and Michoud. The team also observed notable sinking in New Orleans’ Upper and Lower 9th Ward and in Metairie, where the measured ground movement could be related to water levels in the Mississippi River.
At the Bonnet Carré Spillway east of Norco—New Orleans’ last line of protection against springtime river floods overtopping the levees—research showed sinking of up to 1.6 inches per year. Nearby industrial facilities were observed to be experiencing the same level of sinking, according to the report.
“While the study cites many contributing factors for the regional subsidence, the primary contributors were found to be groundwater pumping and dewatering, or surface water pumping to lower the water table, which prevents standing water and soggy ground,” reads an LSU news release.
NASA Jet Propulsion Laboratory scientist and lead author Cathleen Jones says study results will be used to improve models of subsidence for the Mississippi River Delta that decision makers use to inform planning.
“Agencies can use these data to more effectively implement actions to remediate and reverse the effects of subsidence, improving the long-term coastal resiliency and sustainability of New Orleans,” Jones says in a prepared statement. “The more recent land elevation change rates from this study will be used to inform flood modeling and response strategies, improving public safety.”
To fully measure and predict future sinking in and around New Orleans, it’s necessary to better understand the various natural and human-produced processes contributing to the sinking, the report says. Those include withdrawal of water, and oil and gas; compaction of shallow sediments; faulting; sinking of the Earth’s crust from the weight of deposited sediments; and ongoing vertical movement of land covered by glaciers during the last ice age. Jones says the comprehensive subsidence maps produced by this study, with their improved spatial resolution, help scientists to differentiate these processes.
Scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, UCLA and the Center for GeoInformatics at LSU collaborated on the study. LSU has more details.
