Prescient National Geographic

In October 2004, the National Geographic Magazine described what would happen were a decent-sized hurricane to strike New Orleans: disaster, not surprisingly. More interesting to me is the National Geographic‘s explanation of why that disaster was becoming increasingly likely:

Yet just as the risks of a killer storm are rising, the city’s natural defenses are quietly melting away. From the Mississippi border to the Texas state line, Louisiana is losing its protective fringe of marshes and barrier islands faster than any place in the U.S. Since the 1930s some 1,900 square miles (4,900 square kilometers) of coastal wetlands—a swath nearly the size of Delaware or almost twice that of Luxembourg—have vanished beneath the Gulf of Mexico. Despite nearly half a billion dollars spent over the past decade to stem the tide, the state continues to lose about 25 square miles (65 square kilometers) of land each year, roughly one acre every 33 minutes.

A cocktail of natural and human factors is putting the coast under. Delta soils naturally compact and sink over time, eventually giving way to open water unless fresh layers of sediment offset the subsidence. The Mississippi’s spring floods once maintained that balance, but the annual deluges were often disastrous. After a devastating flood in 1927, levees were raised along the river and lined with concrete, effectively funneling the marsh-building sediments to the deep waters of the Gulf. Since the 1950s engineers have also cut more than 8,000 miles (13,000 kilometers) of canals through the marsh for petroleum exploration and ship traffic. These new ditches sliced the wetlands into a giant jigsaw puzzle, increasing erosion and allowing lethal doses of salt water to infiltrate brackish and freshwater marshes.

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