Venice is not the only city in the world that could end under water. With the increase in the global level of the seas, each city and coastal country risks, if not to be submerged, at least to encounter increasing problems, from floods to structural damage caused by the racing of the waters.
One of the most at risk cities in the world is also one of the cities to have suffered a natural catastrophe so large as to spend billions of dollars to protect themselves from future floods. These are New Orleans, who, however, as a study published on reveals Science Advanceswill soon have to update his defenses: While the sea continues to get up, the city is sinking at a worrying rhythmand his alluvial barriers are also doing it.
How much does New Orleans sinks? Hurricane Katrina caused, in 2005, the worst flood of New Orleans’ history, due to the breakdown of the banks that kept the city dry. To repair the damage to the anti-high system, and update it with New barriersthe city of New Orleans expenses 15 billion dollarswhich, however, twenty years later, are proving insufficient. The Tulane University team who published the study has in fact analyzed how much the city is being signed, thanks to a system that puts to Comparison the satellite images of the city taken in the last twenty years and manages to perceive differences in elevation in the order of millimeters.
Avant -garde studies. This technology, which is called Insar, has allowed the team to discover that, if it is true that much of the city is still stable and is not sinking, there are still large areas, both urban and between the surrounding wetlands, where The ground sinks to the rhythm of 2.5 cm a yearwith particularly affected areas in which the rhythm is even half a centimeter per year.
As for what concerns the causes of this phenomenon, which is disconnected from the increase in the water level, they are multiplesomeone natural (the soil compacting is lowered), others linked to the activities human (for example having dried up large wetlands to use water for agricultural purposes).
(No longer) protective barriers. The most serious problem that emerges from the study is that, among the areas of New Orleans they are sinking, there are also alluvial walls, dams and new banks built in post-katrine. This fact, combined with the increase in the level of the seas, means that some of These barriers could prove to be too low today to reject a full one, while they were at the right twenty years ago when they were installed.
Even the fact that wet areas around New Orleans are sinking could have deleterious effects on the city: the swamps could turn into lakes or waterways, losing their function of buffer between the sea and the city. The conclusions of the study are very simple: we must continue to monitor this phenomenon, even at local level, and also think about the opportunity to update the anti-high defensesthat as the city sinks have lost effectiveness.
