DETAILED SURFICIAL MAPPING OF SMALL ISLANDS FOR COASTAL MANAGEMENT, PUERTO RICO

Understanding how shorelines respond to rising sea level is critical for developing sound coastal management and land use planning guidelines, and is even more important when considering the rise effect on small islands. Assessing potential shoreline change and associated land loss on four associated Puerto Rican islands as a result of continuing sea-level rise, is part of an on-going study of small islands and cays around Puerto Rico and the U. S. Virgin Islands. The islands for this study were selected because they exhibit either historical, cultural, recreational, or scientific importance, or some combination of factors.

Although remote sensing is very useful in ascertaining the vulnerability of coastal regions, it can be difficult to accurately capture details of island geomorphology, coastal processes, topography, and the geologic framework. Historical imagery may not possess the resolution needed to adequately map some of the pertinent variables, especially for smaller islands where coverage may be limited and certain variables such as geomorphology are difficult to resolve. Thus, detailed field studies were undertaken to map such variables in high resolution to help ensure a more reliable and robust coastal vulnerability assessment. Islands were mapped using a real time kinematic (RTK) GPS, providing sub-centimeter accuracy both horizontally (Lat/Long) and vertically (elevation) to delineate the apparent high water line. High-resolution shoreline data will also be used in subsequent shoreline change analyses and forecasting. A detailed topographic survey was performed to map the relief and slope of the island. A digital terrain model (DTM) was generated to assist with both GIS-based analyses and visualization of coastal vulnerability. The DTM will also provide a baseline for each island and will be used in future studies of coastal change with future RTK-GPS or LIDAR surveys. The data were used to calculate shoreline recession rates. Geomorphic change models are used to predict land and habitat loss as controlled by varied island settings, providing a scientific basis for planning and management.