Abstract

MEDEIROS, Nãnashaira; DIAS, Marcelo Sperle; AYRES NETO, Artur  and  MUEHE, Dieter. Acoustic mapping of submerged sands deposits for Rio de Janeiro beach nourishment, Brazil. RGCI [online]. 2014, vol.14, n.1, pp.149-158. ISSN 1646-8872.  https://doi.org/10.5894/rgci429.

The Brazilian coast is affected by different oceanographic characteristics, mainly due to its large latitudinal extension. Additionally, the distribution of the Brazilian population is characterized by a high concentration in the coastal capitals. Consequently a large number of coastal engineering structures where constructed in these areas with impact over the sediment transport and consequently over the sediment budget. Natural processes as temporary alterations of longshore sediment transport have resulted in loss of beach sediments and the need of restoration as was the case of the Leblon Beach in Rio de Janeiro. Considering also the expected modification of climate and sea level rise the need of beach restoration will become an option to be considered. For this, the beach restoration through nourishment with sand extracted from the continental shelf is frequently the best option to consider. To find suitable sediments for dredging in the shelf, the use of geophysical methods for the mapping of the bottom and sub bottom environments represent an adequate tool. Therefore the objective of this study is the application of geophysical methods for the identification of geoacoustics patterns, following qualitative and quantitative analyzes, in order to identify suitable source areas of siliciclastic sands for the restauraration of urban beaches in Rio de Janeiro city. The mapping was done in the shelf in front of Itaipuaçu beach (Maricá, RJ). From geophysical data analysis, by quantitative and qualitative form, five geoacoustics patterns where identified which in turn where correlated with grain size parameters obtained through sieve analysis. The quantitative results showed well sorted suitable median grain size sand placers seaward of the closure depth, located between 19 and 30 meters, while reflection seismic data indicated an availability of enough material for the restoration of most of the urban ocean beaches of Rio de Janeiro.

Keywords : Geological Oceanography; Geophysics; Side Scan Sonar; Beach Nourishment; Coastal geomorphology.

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