TROUBLE IN PARADISE: COASTAL EROSION IN RINCÓN, PUERTO RICO

The picturesque coastline of Rincón, Puerto Rico is comprised of Quaternary alluvial deposits bounded by headlands of Tertiary rocks. The 8 km of sandy beaches between headlands are a mix of clastic and carbonate material derived from local rivers, erosion of alluvial uplands, and adjacent coral reefs. This coastal zone also has a bounty of natural and economic resources. Some of the best surfing breaks in the western North Atlantic are located here, where the insular shelf is only ~1 km wide. The Tres Palmas Marine Reserve lies just off the beach. A large public beach fronts the downtown area. Local fishermen's groups have facilities at several locations along the beach. A marina was constructed in the early 1980s. Several large tourist hotels have been built along the shoreline since the late 1990s.

Rincón also has a major coastal erosion problem. For the past 70 years, the central part of Rincon's shoreline has been retreating at about 1 m/yr. The human response to shoreline erosion has been a piecemeal seawalling of the shoreline to protect adjacent property. This has resulted in the narrowing or complete disappearance of many fronting beaches.

Long-term shoreline change data spanning 1936-2006 suggest that the relatively rapid rate of shoreline retreat in Rincón is not an entirely recent phenomenon, and likely predates most human modification of the shore. High-resolution lidar bathymetric data show a complex nearshore bathymetry, including elongate, shore-parallel troughs up to 20 m deep and a lobate sandy shoal that extends across the shelf. These features may strongly affect wave refraction, diffraction, and reflection in areas where erosion rates are the highest. Historical photographs show a wide array of complex wave patterns that suggest bathymetric effects on nearshore processes are a long-term, rather than recent, phenomenon. In addition, sand mining and shoreline armoring may be contributing to the expansion of the zone of most rapid erosion. Local government and community groups are keenly aware of the environmental and economic importance of healthy beaches. Data from previous and future studies should provide a foundation from which to identify the underlying causes of the observed erosion and develop potential adaptation strategies.