Caracterização morfológica e sedimentar da planície costeira e vulnerabilidade do litoral de Jaconé-Saquarema (RJ) às ondas de tempestade

Abstract

The coast of Jaconé and Saquarema have been urbanized in an intense and fast rhythm, by building urban structures and construction engineering on the sandy barrier and near to the beach. In the last decades, storm surge events have been occurred in a more intense scale, causing the buildings’ destruction and floods on the coast. Considering the high level of dynamic and the changes in progress, it is necessary to keep under observation the Jaconé and Saquarema beach arc, so that we can understand this environment’s response to all these transformations in the coastal landscape. Therefore, this study aims at the morphological and sedimentary characterization of the coastal plain of Jaconé-Saquarema and to point out the most vulnerable areas of this coast to the storm waves. The study area comprises the municipalities of Maricá (to the west) and Saquarema (to the east), respectively and this coastline is compound of a rich biodiversity, in addition to the presence of beachrocks, which is an element of great importance for local geodiversity. The methodology of this study included 7 field surveys for the acquisition of 58 topography data and collection of 78 sediments samples along the coastal plain; mapping to characterize the remaining geomorphology and urbanized areas in the coastal plain; Seasonal monitoring of beach dynamics through the acquisition of topographic profiles and the collection of sands for granulometric analysis, morphoscopy and sediment volume calculation. At the beach, 9 sites were selected for monitoring during the summer and winter seasons. The results show a very modified coastal plain due to the rapid urban growth, most strongly concentrated in the eastern beach arc’s sector, where the geomorphology is quite uncharacterized. The beach indicate a moderate to high level of dynamic, with intense energy of the storm waves and their interaction with the coast in the extreme west of Jaconé (profile 1), with a slight decrease in energy towards Saquarema (extreme east). The west sector (in the area of profile 2) exhibited the smallest variations in width and morphology, due to the presence of the beachrocks of Jaconé, which partially intersect high energy incident waves along this specific beach area. The sediments that constitute the coastal plain are composed of quartz sands, moderately selected, well rounded to subangular, with a decrease in grain size from west to east, ranging from very coarse to medium sand, respectively. The same occurs in the sand strip of the beach, except in the west sector where the beachrocks, located in the zone of foreshore and along 1 kilometer, acts as a parallel barrier to the water line allowing the accumulation of fine and very fine sand, poorly selected, in the post-beach area, contrasting with the high wave dynamics so characteristic in the study area. The high dynamics observed in the beach arc and the damages caused by storm surge in recent years point to a high vulnerability of this coast to storm waves. The dynamic behavior, coupled with the environmental changes in progress and the existing problems in the Jaconé and Saquarema coastline, must be carefully analyzed before any type of intervention related to the installation of construction engineering and to subsidize the decision to be taken related to coastal zone management.