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Tropical storm Barry causes storm surges and flood warnings: Why is New Orleans exposed to increased risk?



As tropical storm Barry continues to bombard the Louisiana coast, floods and precipitation are of growing concern, particularly for the city of New Orleans, which is more vulnerable to severe weather events.

According to forecasts, Barry will dump 10 to 20 inches of rain over New Orleans until Sunday. Some isolated areas could see up to 25 inches.

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But why is this historic city more exposed to floods than other parts of the state? Read on to discover some of the factors that have increased the risk of "Big Easy".

Low altitude

New Orleans is particularly vulnerable to flooding because of its low altitude, according to the University of Wisconsin-Eau Claire. About half of the city is above sea level – a drop from what was once 100%, according to the Atlantic, which cites human interference as the leading cause of the sinking of the sea. city. A 2016 NASA study also stated that "natural geological" factors played a role.

"When New Orleans was built, they ran out of good land. To make more room, the engineers drained the swamps around the area in order to continue their expansion. This drainage has led to subsidence, "said Wisconsin-Eau Claire, noting that the subsidence is" falling apart or moving to a lower level. In this case, it was the surface of the Earth that was sinking lower than the sea level.

Even some of the city's earliest settlers – mainly in the French Quarter of New Orleans, the original part of the city – were able to build their homes on raised land. Those who had the "means and resources" built houses on "prime real estate" – or on land about 10 feet from sea level, wrote the FEMA (Federal Emergency Management Agency) in its "History of the height of the buildings in New Orleans".

"Even in its infancy, New Orleans residents had understood the value of the land overlooking the flood-prone lands that they had chosen to call their home," the agency adds.

Lift construction

In 1719, the first lift was built in New Orleans. The first among many others along the Mississippi, those who built it were aware of the "paramount importance of elevated or at least protected land in the city," according to the FEMA report. .

But dike construction would later contribute to subsidence.

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The city is located between the Mississippi River and Lake Pontchartrain levees. According to the University of Wisconsin-Eau Claire, this creates a "bowl effect" in the city. Basically, once the water comes in, it's hard to remove it.

Wetlands and endangered barrier islands

New Orleans is also prone to flooding as the city is exposed to storm surges, or "abnormally high levels of seawater during a storm," according to the National Ocean Service. It is measured by the water level of the normal astronomical tide.

Wetlands and barrier islands serve as a natural defense against storm surges. In fact, "for every thousand continuous wetlands, a storm surge can be reduced by three to eight inches," according to the university.

"Wetlands are naturally replenished each year by the sediments of a flooded river" if these areas are not disturbed, the university added. But wetlands and coastal islands near New Orleans have disappeared at an "incredible rate" due to human interference.

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"The dams upstream of the city have reduced the amount of sediment in the river by 67%. [percent]Affirms the university.

"At the same time, the dikes built around New Orleans to protect it are now diverting the flow of the river into the Gulf of Mexico, which means that much of the remaining sediment is dumped into the sea and not deposited. in the barrier islands. These factors prevent the best defenses of nature from being reconstituted and make them disappear. "

In fact, every hour and a half, Louisiana loses about a football field, the New Yorker said in a report released in March.

Associated Press contributed to this report.


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