New Orleans is singularly exposed to the fury of hurricanes because it is largely below sea level. The city is often described as a "bathtub" surrounded by an elaborate, expensive, and elderly series of levees; sinking about a half-inch per year as the river sediment it is built on decomposes and compresses; losing protection from barrier islands and wetlands between the city and the Gulf of Mexico, which slow a hurricane's winds and reduce its storm surge. Louisiana is losing an estimated 34 square miles of land per year, the fastest wetland destruction in the nation. In another 50 or 100 years, New Orleans could have frontage directly on the Gulf.

 

WETLAND RESTORATION SEEN AS CRUCIAL Delta's marshes, islands form buffers against storm surges, scientists say Glen Martin, Chronicle Environment Writer Monday, September 5, 2005 The catastrophic flooding of New Orleans was long predicted by scientists, and researchers are now promoting a way to avoid similar disasters in the future -- a Manhattan Project-style effort to restore the barrier islands and vast marshes that once protected the city from the sea and storms. Scientists note that over a period of 7,000 years, the Mississippi River created a huge delta that sheltered the region now supporting New Orleans from storm surges. But the delta -- and its wetlands and islands -- have been steadily shrinking since 1930, thanks to river diversion projects that have prevented the river from depositing silt and sand at its mouth. Instead, the sediment has been directed further offshore, beyond the continental shelf. To ensure that a catastrophe like Katrina won't be repeated, say scientists, a significant portion of the old system must be reconstructed. "New Orleans won't be safe from another storm like Katrina until we restore this hurricane buffer," said Robert Twilley, a professor of wetland science at Louisiana State University and the leader of a team overseeing a $2 billion marshland rehabilitation project in the state. "But protecting New Orleans will take a lot more than $2 billion," said Twilley. "A very rough estimate is $14 billion," he said. Prior to the European settlement of the area, about 3.6 million acres of marsh and an extensive system of sandy offshore islands surrounded the mouth of the Mississippi River, protecting inland areas from the worst effects of storm surges and waves, said Twilley. These marshes and islands were the direct handiwork of the river, which continually dumped sediment into its delta, Twilley said. The Mississippi's outlet would shift over time, from east to west and back again, constantly building up new islands and wetlands with the sand and silt harvested during the river's course through North America. "Wetland loss was part of the process, but it was always accompanied by wetland gain," Twilley said.