BEACH ACCRETION AND EROSION CAUSED BY THE STORM SURGE OF THE SEPTEMBER 2, 2004, HURRICANE FRANCES ON THE ISLAND OF SAN SALVADOR, BAHAMAS

The impact of Hurricane Frances that directly hit San Salvador, Bahamas as a Category 3 hurricane on 09/02/2004, was investigated from satellite imagery and field mapping in March 2005. Landsat 7 Enhanced Thematic Mapper images of San Salvador from before the storm (Aug. 30) and after it (Oct. 10 and Dec 4) were analyzed to determine areas to measure the storm surge impact and regions to focus our field research. Our main focus was documenting storm surge deposits and beach accretion and erosion processes on the southeastern coast of the island from Dim Bay to Sandy Hook. These areas clearly show a significant reworking of sand and potential loss of vegetation in other areas. Other areas of the island also showed significant changes in beaches, but were not studied at this time. Storm surge washover height and beach profiles were measured by using a hand level and a 1.5 m stadia rod divided into 10 cm increments. The distance from high tide to areas of interest were measured using the pace method. Maximum storm surge washover based on transect data was estimated at 4.8 m along the south end of Storr's Lake. Large boulders (up to 70 cm by 90 cm) of beach rock had been ripped up along the southeast beaches and Sandy Hook and were imbricated by the storm surge from Hurricane Frances. Mangrove vegetation line retreat was paced out to be 43 m on Sandy Hook. The adjacent beach to the south showed signs of accretion to a measured width of 25 m. The south side of Sandy Hook is composed of lithified Pleistocene reef which is highly resistant to beach erosion. Some blocks in addition to trash and vegetation were washed inland into the south end of Pigeon Creek in the storm surge. Evidence of Frances and other storms were also found in stratified trash deposits south of and around "The Thumb". A 1.7 m thick section was measured that showed 80 cm of aeolian sand burying a 40 cm-thick horizon of stratified trash. At this location Hurricane Frances deposits were found at higher elevations and further inland. These data indicate the Hurricane Frances storm surge was more intense than the previous three hurricanes that hit the island during the 1990's.