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Revista de Gestão Costeira Integrada

versão On-line ISSN 1646-8872

Resumo

OLIVEIRA, Julio F. de  e  MUEHE, Dieter. Identification of the occurrence of compatible sediments for beach nourishment in the inner continental shelf between the towns of Niterói and Macaé - Rio de Janeiro, Brazil. RGCI [online]. 2013, vol.13, n.1, pp.89-99. ISSN 1646-8872.  https://doi.org/10.5894/rgci362.

The occupation of the coast of Rio de Janeiro State, eastward of the Guanabara Bay, have been submitted to a strong and continuous occupation, first due to the expansion of second residences as in Armação dos Buzios, Cabo Frio, Arraial do Cabo, Saquarema and Maricá with a sharp increase after the construction of a bridge over the Guanabara Bay on 1974, allowing an easy and rapid connection between the city of Rio de Janeiro and the east coast, stimulating the tourism, the expansion of the metropolitan area of Niteroi and the urbanization of the coastal area in general. Northward of Cape Frio, the exploration of offshore oil in the Campos Basin at the end of the decade of 1970, with the city of Macaé as the main hub, triggered an additional boom of occupation with expansion to the town of Rio das Ostras. The construction of houses and buildings in the immediate proximity to the beaches, as a valued location in the urbanization process, resulted in a vulnerability which became apparent after the localized destruction of proprieties through coastal erosion after a few extreme events. The coastal vulnerability tends to increase with climate changes due to the expected increase of intensity and frequency of storms as also the increase of the sea level. In this sense, the possibility of protection through beach nourishment has been suggested with some frequency which focuses on the necessity of an inventory of suitable sources of sand. This paper presents an initial approach to identify potential sources of suitable material on the inner continental shelf in front of the east and south-eastern coast of the state of Rio de Janeiro. For this purpose the grain size characteristics of sands of the different urban beaches were compared with the characteristics of bottom sediments of the inner continental shelf. Sediments were collected at the beach face of the potentially most endangered beaches and submitted to a conventional grain size analysis through dry sieving. The grain size distribution of the inner continental sediments where already available from prior expeditions. The comparison and classification of compability was made through the applications of the overfill ratio diagram from James (1975) which allows an evaluation of the amount of borrow material which will be retained on the beach in relation of the amount of sand deposited, considering the mean grain size and standard deviation of the beach and of the borrow material. Eleven areas offshore of the 200 km long coastline were identified, representing areas to be submitted to a detailed investigation through seismic profiling and coring in order to evaluate the amount of material available for beach nourishment followed by an evaluation of the impact of the morphological modification of the sea floor over the wave propagation as also over the impact of dredging to the benthic community.

Palavras-chave : Beach Nourishment; Borrow Areas; Suitable Sediments; East and South-Eastern Coast of the State of Rio de Janeiro.

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