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Flood-prone New Orleans sinks at a rate up to 2 inches per year, study finds

A new study has found that flood-susceptible New Orleans and the surrounding metropolitan area continue to sink due to a combination of natural geologic and human-induced processes.

The highest rates of sinking, up to 2 inches per year, were observed upriver along the Mississippi River around major industrial areas in Norco, Louisiana, and in Michoud, an area in eastern New Orleans.

Notable amounts of subsidence, the gradual sinking of an area of land, were also detected in New Orleans' Upper and Lower 9th Ward as well as Metairie, Louisiana.

Research showed up to 1.6 inches a year of sinking at Bonnet Carré Spillway east of Norco, which is New Orleans' last line of protection against springtime river floods overtopping the levees, a NASA press release said.

The study cites a number of reasons for the regional sinking with the two primary reasons being groundwater pumping and detwatering, a process where surface water is pumped to lower the water table which in turn prevents standing water and soggy ground.

Other natural and human-produced factors included withdrawal of water, 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.

Jet Propulsion Laboratory scientist and lead author of the study Cathleen Jones said in a press release the that the 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 said.

Jones said that the recent land elevation change rates found from this study will also be used for flooding response strategies and improving public safety.

With an estimated population of 389,617 in New Orleans, sinking raises flood concerns for an area that is already vulnerable.

"The Mississippi River delta is losing its natural coastal barriers -- the delta wetlands and barrier islands -- increasing flood risk across the area," the NASA press release said. "In response, the region has increased investment in infrastructure and restoration activities to protect human populations and areas of high economic value."

According to AccuWeather Senior Meteorologist Dan Kottlowski, New Orleans is prone to flooding due to the swampy area the city was built on.

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"As a result, they have a high water table and need to pump water on a large scale to keep some areas from experiencing flooding," Kottlowski said.

Kottlowski added that whenever a significant rainfall occurs or excess water comes down the Mississippi River from the north, New Orleans will endure flooding.

"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," as stated in a press release.

The study, which was published in the Journal of Geophysical Research: Solid Earth, was a collaborative effort between scientists at NASA's Jet Propulsion Laboratory, UCLA and the Center for GeoInformatics at Louisiana State University. It covered the time period between June 2009 to July 2012.