Dinâmica de praia e vulnerabilidade às ondas de tempestades do litoral oriental da Ilha Grande (Angra dos Reis - RJ)

• Autor(a) principal: Gralato, Jaciele da Costa Abreu
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/13457
• topic: Coastal dynamics; Sedimentology; Ilha Grande; Dinâmica costeira; Sedimentologia; Ilha Grande; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOGRAFIA FISICA

The objective of the present study was the characterization of the beach dynamics and vulnerability to storm waves of the eastern shoreline of Ilha Grande (Angra dos Reis, Rio de Janeiro State). Through the knowledge of the morphological and sedimentary dynamics it has been possible to identify the beaches vulnerable to erosion and damage. Ilha Grande is the biggest island of the southern coast of Rio de Janeiro State, with 193 km², mostly covered by remains of the Atlantic Rain Forest. Despite all the efforts to preserve the magnificent environment, through the creation of conservation unities, the present-day scenery is alarming because of an increase of the tourism and lack of basic sewage treatment plants on the island, as well as the expansion of oil and nuclear activies. Ilha Grande is formed by more than one hundred beaches, up to now unknown from the geomorphological point of view. The beaches selected for this work were Vila de Dois Rios and Lopes Mendes on the island s shore facing the open water of the Atlantic Ocean, and Vila do Abraão and Pouso on the island s shore facing continent. Seazonal beach was carried on for two years, obtaining 45 topographic profiles and 126 samples, from the subaereal and submarine parts of the beach; the samples underwent grain-size and morphological analyses. The results allowed the characterization of beach dynamics and the evaluation of the vulnerability to storm events of the eastern shoreline of Ilha Grande. The studied beaches present distinct geographic and geomorphological characteristics and can vary from few hundred meters to several kilometers in length; they also present different degrees of exposure to the oncoming storm waves depending upon their location and orientation. Dois Rios beach and mainly Lopes Mendes beach are the most dynamic and vulnerable to storm waves. Lopes Mendes, in special, showed strong longshore current and rip currents in the center of the beach arc, which form prominent channels on the beachface; major storm events remove large quantities of the barrier s sediments causing the exposure of trees roots and finally their fall. Abraão and Pouso Beaches, facing the continent, even though presenting, respectively, low and moderate dynamics, are also vulnerable to storm waves. The sediment dynamic of the study area is characterized by the mobility of the sands between the exposed and submarine parts of the beach. Lopes Mendes and Dois Rios Beaches show, in addition to that, longshore transport of sands. Grain size and sorting showed considerable variation among the studied beaches: fine to very-fine subangular quartz-rich sand predominate on Dois Rios and Lopes Mendes, with sorting degree decreasing from the backshore to the beachface; Abraão and Pouso present medium to very-coarse subangular quartz-rich sands, and poor sorting on Abraão and very well-sorted sands on Pouso beach. These variations on grain size and sorting respond to the influence of coastal and fluvial processes and indicate that the small river and the inner continental shelf are the main sources areas for the investigated beaches.