HETEROGENEOUS VULNERABILITY TO HURRICANE JOAQUIN’S INFLUENCE ALONG THE PERIMETER OF SAN SALVADOR ISLAND, BAHAMAS

Effects of Hurricane Joaquin (Sept/Oct 2015) were highly variable on the perimeter of the small, exposed Bahamian island of San Salvador. Following the USGS storm impact scale method, the geological effects of Joaquin were assessed relative to foredune elevation and swash height. Damage was categorized, in order of increasing severity, as: swash, collision, overwash, and inundation damage. Assessment of 9 representative regions was undertaken in Jan 2016 using orthophotos and digital elevation models generated from drone flights, georadar, and ground surveys.

Storm surge was not a critical factor for most of the island, and persistent flooding and breaching of coastal barriers was not common. Consequently, minimal overwash and inundation damage occurred. The south shore was an exception, where wave action was extreme. Here, 5-m-high cliffs were overtopped, causing erosion at the leading edge and extensive landward movement of boulders within a 6.3 ha area. New boulders, as large as 3 m in diameter, were generated, and older blocks from prior storms, estimated to weigh 1-3 tons, moved up to 26 m inland. The principal road was damaged and inundated by debris. Along the east (windward) and west coasts, hurricane impact caused substantial dune scarping and some overwash, though no dune systems were breached. Overtopping into the backdune occurred at numerous locations along both coasts, onto the circum-island Queen’s Highway, and into several swale lakes. Scarped dunes lost as much as half their volume with retreat as far as the dune crest. Some dune scarps at the time of assessment had already shown signs of eolian repair. These scarps will remain as recognizable subsurface features in future geophysical images. A rejuvenated tidal channel was scoured along the southeastern coast, establishing an ephemeral connection to Pigeon Creek, and a massive overwash fan of approximately 1 ha now blocks the mouth of this channel. Overall, no significant, irreparable coastal change occurred as a consequence of Joaquin. Although the storm imposed economic hardship, much of its geomorphologic legacy is already being modified by fair-weather processes. Because of the potential consequence of future storm activity, we recommend that a comprehensive assessment of storm vulnerability be undertaken throughout the archipelago.