LOW-RESOLUTION ANALYSIS OF MORPHOLOGICAL CHANGES ON THE GRAND TERRE ISLANDS, LOUISIANA AND EVALUATING THE LARGE-SCALE IMPACT OF TROPICAL CYCLONES ON ISLAND EVOLUTION

Grand Terre, once a large barrier island protecting Barataria Bay in the 1800's, fragmented into two islands in the early 1900's: resulting in the modern East Grand Terre and West Grand Terre. Since the fragmentation, West Grand Terre has evolved differently from East Grand Terre, most notably because longshore transport to East Grand Terre has allowed for the development of encapsulated bays which resemble cat-eye ponds. These two islands are the main barriers currently protecting Barataria Bay and its subsequent wetlands so understanding their evolution in the presence of large-scale restoration/renourishment efforts is paramount.

For both of these islands, shoreline erosion is the dominant trend with an average long-term shoreline loss of 5.4 m/yr on West Grand Terre and 12.5 m/yr on East Grand Terre. A separate trend, present only on East Grand Terre, is the growth of a spit that started to encompass the backbarrier bay (Bay Melville) during the mid to late 1980's and completely captured it by the year 2000. The long-term growth rate from 1984 to 2000 was 113 m/yr with a total growth of 1,846 meters in length. Additionally there were some periods of rapid growth such as the period between 1990 and 1991 with a growth rate close to 400 m/yr. Landsat satellite imagery, despite the restrictions imposed by resolution, allows for nearly continuous observations of the island-spit growth through time as well as storm induced changes; providing a model for Louisiana master plan objectives.