Erosão e progradação da linha de costa de Icaraí de Amontada - Ceará

Abstract

The beaches are one of the most dynamic environments on the planet earth, due to the direct influence of the waves, tides and winds and are therefore rapidly modified. Faced with this, the shoreline is the first to undergo variations, which guarantees greater mobility along the beach. The Icaraí de Amontada beach, located on the west coast of the state of Ceará, is classified as sandy beach with occurrence of fixed dunes, frontal dunes and eolianites, being, therefore, a great part of the contribution of sediments carried out by the wind transport. The motivation on the accomplishment of this study was to understand the space-time dynamics of the shoreline variation, in order to characterize theenvironment as to the levels of erosion and progradation of the beach between the years 2003 and 2018. For this, the methodology used consisted of bibliographical surveys related to the study area and morphodynamic processes of coastal circulation, cartographic survey, topographic survey and sample collection. For the analysis of the spatial-temporal variation of the shoreline, Quickbird images from the years 2003, 2004, 2010, 2013, 2014, 2015 and 2018 were used and an orthophoto provided by SEMACE (State Superintendence of the Environment) for the last Ecological Economic Zoning (ZEE in Portuguese) in the state of Ceará. The DSAS 3.2 extension of the ArcGIS software was used to calculate the shoreline retreat. The field experiment was carried out on October 09 and 10, 2018 and consisted of data collection for positioning of the shoreline through the use of RTK 6 equipment of the Trimble brand, realization of six beach profiles in the study area with the RTK and collection of sediments from the region of theforeshore, intertidal zone and backshore in each one of the profiles. In addition, there was also the RTK trek in a frontal dune area to elaborate a Digital Terrain Model (DTM) to analyze the flood and erosion rate of the area. The results showed that the beach of Icaraí de Amontada, in the interval of 15 years, presented a predominantly erosive character, reaching rates of - 2.50 m / year, resulting in a decrease in the beach range of approximately 40 m in the time interval analyzed. It was observed that, although it was predominantly erosive, a sector of the beach, presented progression, reaching maximum values of about 2.03 m / year, totalizing an increase of 32.4 m of beach strip in the interval of time analyzed. This increase is possibly associated to the occurrence of a sandy promontory in the area of the prograding sector, which acts by attenuating the direct incidence of the waves in the region of shade formed by it and also by an abrasion platform in the area, which causes a reduction in the intensity with that the waves arrive on the beach in the region opposite the platform.