Transcript for Hurricane Force - A Coastal Perspective, segment 06 of 12


Armed with their pre-Andrew studies, the scientists set out to determine just how much erosion took place and, more importantly, where the sand went. Changes to the Ile Dernieres Barrier Islands were fairly easily determined as the scientists were able to reoccupy existing survey lines across the islands, giving them a quick and accurate assessment of hurricane-caused erosion on the Ile Dernieres.


Determining where the sand went is of vital importance to the people of the State of Louisiana who hope to dredge the sand up and replace it on the barrier islands. The scientists ran shallow water surveys in the bays behind the barrier islands, comparing sea floor elevations from before and after the hurricane. Areas that are now deeper must have been eroded by the storm, while new shallower areas define exactly where the sand went.

Andrew's erosive storm surge also devastated Louisiana's wetlands, site of a second long-term study involving the National Biological Survey.

The second study, the wetlands study, was started more recently, and its emphasis was to understand the rate of loss of marshland. One of the major problems in the Louisiana coastal zone is that marshland is being transformed into shallow open bays, and once that happens, you lose a lot of the diversity of species. Waterfowl tend to go elsewhere because it isn't the right kind of habitat for them.

Louisiana's wetlands are sinking, a process called subsidence caused by compaction of the huge underlying pile of sediments laid down by the ancient Mississippi River. Combined with certain human influences and gradual sea level rise, new patches of open water are forming at about sixty acres a day. Andrew's storm surge adds yet another cause to the problem of wetlands loss in Louisiana.

The area that we've been working in had a lot of semi-floating mat that - what looked to be solid land is really a thick surf - mat surface, and it's only loosely connected to muddy sediments maybe a few centimeters or up to a meter or so below.

The storm surge lifted the mats up and moved them around, creating new patches of open water. Chunks ripped off the mats became floating mud balls. Accordionlike folds developed where entire sections of mat were pushed against more stable areas. Combined, the work of Andrew's storm surge on both the wetlands and the barrier islands has accelerated an already dire situation in coastal Louisiana. Efforts to mitigate the transition from marsh and wetlands to open water have been dealt a heavy blow by the hurricane.

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