INSIGHTS INTO IMPACTS OF STORMS ON SMALL, LOW-RELIEF, TROPICAL CARBONATE ISLANDS FROM LONG-TERM MONITORING OF COASTLINES ON SAN SALVADOR ISLAND, BAHAMAS

Long-term monitoring of Bahamian island coastlines offers invaluable insights into understanding storm hazards and developing mitigation approaches. Aided by technological advances, such as high-resolution drone imagery and RFID (radio frequency identification) tagging of storm-generated and transported clasts, the monitoring produces compelling datasets about coastal vulnerability for use in communication with various stakeholders. This is becoming increasingly important as consequences of changing climate and rising sea levels are amplified by powerful storms, such as Hurricane Dorian that devastated Grand Bahama and Abaco islands in Sep. 2019.

Our monitoring on San Salvador since 2012 has documented modifications by Hurricanes Sandy (Oct. 2012), Joaquin (Oct. 2015), and Matthew (Oct. 2016) along two morphologically distinct rocky coastlines with storm-deposited boulder ridges. Significant changes were documented after Joaquin, which passed over the island as a Category 3 hurricane with 120-130 mph sustained winds. Storm waves overtopped cliffs on the southern coast, causing erosion and landward movement of boulders. This modified the formerly sharp-crested, narrow boulder ridge into a broad field, stripped of vegetation. New boulders, as large as 3 m in diameter, were generated, and blocks from prior storms, weighing 1-3 tons, moved up to 26 m inland. The seaward edge of the boulder ridge moved landward 4-5 m, exposing a Pleistocene/Holocene boundary terra rossa paleosol and marking extent of storm erosion.

Application of RFID tagging in June 2019 has substantially increased our database by addition of small boulders and cobbles. In conjunction with drone imaging in Jan. 2020, this allowed us to document the impact of cold front winter storms to our relatively protected study site on the island’s gently sloping northern coast in absence of hurricane activity. Smaller size and better rounding of clasts at this site has been used previously to interpret their movement by waves. The combination of RFID and drone-acquired data provided information about the amount and direction of their transport. The new database also includes digital elevation maps (DEM) and transects through study sites for future comparative analyses of their response to increases in sea level and storm intensity.