A MODIFIED COASTAL VULNERABILITY INDEX FOR SMALL ASSOCIATED ISLANDS OF PUERTO RICO AND THE U. S. VIRGIN ISLANDS
Coastal dynamics of small islands differ from that of mainland shores, and therefore a classic CVI analysis was deemed inappropriate. The six variables utilized by the USGS are geomorphology, shoreline erosion and accretion rates (m/yr), coastal slope (percent), rate of relative sea-level rise (mm/yr), mean tidal range (m), and mean wave height (m). Those variables do not comprehensively reflect the features and processes at work on small islands in the region. For example, mean tidal range and mean wave height do not vary significantly over the scale of a small island, and so it was removed from our formula. We utilized parameters of vegetation, storm frequency, beach/bedrock composition, and rates of tectonic subsidence/uplift in addition to geomorphology, shoreline erosion and accretion rates (m/yr), coastal slope (percent), rate of relative sea-level rise (mm/yr), and significant wave height. CVI values were computed twice: once in the original USGS format, and again in the newly modified format.
Small islands require much more detailed investigations due to heterogeneity across small distances. In addition, other hindrances in a vulnerability assessment of this nature include data gaps, methodological difficulties, and island accessibility. To address these issues, detailed field mapping was completed for two islands: Cayo Ratoñes and Isla de Cardona. This has resulted in a very general and preliminary vulnerability assessment for the small islands of Puerto Rico. However, once finalized, similar methods may be applied and refined for the mainland coast Puerto Rico and the Caribbean region.