A COMPREHENSIVE STUDY ON COASTLINE PROCESS AND SEDIMENTARY DYNAMICS, SARDINERA BEACH, MONA ISLAND, PUERTO RICO

Sardinera beach located on the western side of Isla de Mona, Puerto Rico, was investigated to document shoreline changes and seasonal variations in sand movement, sand composition and beach geometries. The strategic location of Sardinera beach in an area far from main land and with scarce man-made influences make this an important research place to gather information on shoreline processes. During the last decade the recreational and ecological value of Sardinera Beach has been affected by a considerably increase on beach rock exposure. In order to provide information about the shoreline changes in Sardinera Beach ten permanent beach profile were established along the beach, sand samples were collected from the berm, swash and nearshore on each beach profile and additional samples were collected from adjacent beaches, reef and shelf zones, and aerial images from 1970’s to 2007 were used to estimate coastal variations. Sardinera Beach sands are composed mostly of carbonate (CaCO3) components that resulted from a combination of biological, chemical, diagenetic, and micritization processes. Differences in sand composition between Sardinera beach, Mona shelf, adjacent beaches, reef crest and reef lagoon suggest that Sardinera sands are not replenished by modern marine components. Sardinera’s micritized and recrystalized sands seem to have been re-transported between the reefal lagoon and the beach, while the input of “fresh bioclasts” seems to be limited by natural (beach rock) and man-made (dock) barriers along the shore line. In addition the input of “fresh bioclasts” seems to be affected by the man-made aperture of the reef system in front of the beach, which altered the direction of natural current patterns on the beach. The sand volume analysis indicates a total sand loss of 1,322 m3 between the months of September to April and the analysis of aerial images from the 1977, 1992 and 2003 shows recession of ~14 to 27 meters along the coast line.