Wetlands Loss Connection To Katrina's Devastation Becoming Clearer - BBC

[hatrack]

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The river itself has changed course many times as it naturally seeks the line of least resistance to the Gulf of Mexico - and that is what forms the delta shape. Deltas are naturally inclined to sink, but in the past this was counteracted by the new deposits of silt dumped on the land as the river floods each year. This process has been interrupted by the widespread system of embankments or levees which have been constructed along large parts of the river over more than a century. In addition, the extraction of oil and gas from rock layers underneath the delta is believed to have speeded up the subsidence, according to research by the United States Geological Survey.

Coastal scientists have been arguing for years that the re-engineering of the delta was leaving the population living there dangerously exposed to storm surges created by hurricanes. An especially controversial project was the construction in the 1960s of the Mississippi River Gulf Outlet (MRGO), a 200m wide canal designed to provide a shortcut for large ships from New Orleans to the ocean. The canal, known locally as "Mr Go", drove straight through an area of dense swampland, and local people have been campaigning for years to get it closed, claiming that it provided a "hurricane highway" which threatened the communities east of the city.

Mark Davis of the Coalition to Restore Coastal Louisiana told the BBC News website the shipping traffic had never materialised. "And as we see in the wake of Katrina, it provided a funnel in its levees and other structures, for bringing storm surge in huge concentrations to communities where people lived and worked, and wiped them out," he said.

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According to new modelling and field observations from Louisiana State University, the MRGO may have made the storm surge 20% higher, and two or even three times faster as it crashed into the city. Hassan Mashriqui of the LSU Hurricane Center said, "We found out that wherever the Gulf Outlet had eaten up more wetlands and exposed the levee system, that is where much more breaches happened. "Where there were tree lines protecting the levees, they were in much better shape. "It is fair to say that the Gulf Outlet played some role in making the situation worse."

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http://news.bbc.co.uk/1/hi/world/americas/4393852.stm