The coast from Punta Higuero to Punta Cadena in Rincon, Puerto Rico is experiencing long-term erosion. This study documents historical shoreline changes at Rincon for the period 1936-2006 and constitutes a significant expansion and revision of previous work. The study area extends approximately 8 km from Punta Higuero to Punta Cadena. Fourteen historical shoreline positions were compiled from existing data, new orthophotography, and Global Positioning System (GPS) field surveys.
The study area can be divided into four distinct reaches on the basis of observed erosion rates, consistent with previous work. The coast of Reach A, from Punta Higuero to the north end of the Balneario de Rincon, is fairly stable and has a long-term (70 years) average erosion rate of -0.2 ? 0.1 m/yr. The coast of Reach B, from the Balneario de Rincon to 500 m south of the mouth of Quebrada los Ramos, has an average long-term erosion rate of -1.1 ? 0.3 m/yr. The coast of Reach C, from 500 m south of the mouth of Quebrada los Ramos to Corcega, has an average long-term erosion rate of -0.4 ? 0.2 m/yr. The coast of Reach D, from Corcega to Punta Cadena, has an average long-term change rate of -0.2 ? 0.2 m/yr.
Previous work (Thieler and others, 1995) identified an apparent increase in erosion rate in Reach B that probably began between 1977 and 1987. New data and statistical analysis suggest that long-term and short-term rates of shoreline change are statistically similar. Nevertheless, the coast in Reach B is eroding at a rapid and statistically significant rate that is 2 to 10 times greater than in the other three reaches. Comparison of the 1994 and 2006 GPS shoreline positions indicates the following erosion rates occurred over the past 12 years: Reach A, -0.3 ? 0.4 m/yr; Reach B, -1.0 ? 0.4 m/yr; Reach C, -0.7 ? 0.4 m/yr; and Reach D, -0.3 ? 0.4 m/yr.
Thieler and others (1995) speculated that the increased erosion rate in Reach B could be attributed to the effects of marina construction in 1983 on the local sediment budget. New data and analysis suggest, however, that other factors may be equally or perhaps more important. For example, high-resolution lidar bathymetric data collected in 2001 show a complex nearshore bathymetry that may substantially affect wave refraction, diffraction, and reflection in Reach B where erosion rates are the highest. In addition, several historical photographs dating from 1951 to 2006 show a wide array of complex wave patterns that suggest the bathymetric influence on nearshore processes to be a long-term, rather than recent, phenomenon. In addition, removal of sand from the beach system may be contributing further to the elevated erosion rates in Reach B.
Development of potential options for addressing coastal erosion in Rincon was beyond the scope of this study, but the data and interpretations presented here provide a sound scientific foundation for further work to identify the causes of the increased erosion and to develop strategies to mitigate its effect.