The morpho-sedimentary analysis of the beach shoreface inner continental shelf system in front of the National Park of the Restinga de Jurubatiba - Rio de Janeiro

Abstract

The morpho-sedimentary analysis of the beach-shoreface-inner continental shelf system in front of the National Park of the Restinga de Jurubatiba – Rio de Janeiro was undertaken in order to characterize and to identify the hydrodynamic and morpho-sedimentary processes in the related system and to make a further analysis of the application of the concept of equilibrium profile (Dean 1977). It evaluated the hypothesis that the coating on shoreface sediment doesn’t control the shape of the profile of equilibrium, being the substrate of relict shoreface the dominator in such a format. An analyzis of historical and geomorphological, sedimentological and oceanographic area and field observations allowed us to evaluate the stability of the shoreline. The strong erosion observed in different segments of the beach was clearly related to variations in South, Southwest and South-Southwets wave height, orientation of the shoreline as also to sediment characteristics of the shoreface and the inner continental shelf. The occurrence of patches of very fine sand and mud in the shoreface inhibited the onshore transport of medium to coarse sands to the beach leaving to the littoral drift the main function in providing the sediments for the equilibrium of the beach. The transgressive history of the geologic-geomorphologic evolution of the area also favors the instability of this coast. The observed morphologic disequilibrium in the beach is partially compensated by the volume of mobilized sediments through the northward directed longshore transport. Therefore modifications of the resulting direction or intensity of the longshore sediment transport due to modification of the wave climate will result in increased instability of a system already under stress