Sediment Characteristics of an Impacted Coastal Bay: Baia de Guanabara, Rio de Janeiro, Brazil

Baia de Guanabara is one of the largest and most important bays of the Brazilian coastline. Over recent years coastal erosion problems have been registered there, mainly due to increasing urbanization and industrial development related to the oil and gas industry. This paper presents the results of an experimental program aimed at obtaining the rheological and sedimentation properties of the sediments that are on the pipeline routes in the bay. With this information it is possible to assist the municipality in reducing beach erosion and implementing sustainable measures for better coastal development. It was found that the sediments from Baia de Guanabara have sedimentation rates ranging from 0.63 to 13.25 cm/min. Solid content is relatively low, consistent with the fact that they are unconsolidated sediments. The particle size distribution of the sediments reflects the depth of the water column of Baia de Guanabara; the deeper the water column, the coarser the sediment. However, the sediment shows plasticity, suggesting the presence of organic matter derived from the 20 m(3)s(-1) raw sewage discharged into the bay. Fine sediments are found near shore; these are fluvial in origin or come from diffuse pollution sources. Their activity is high, indicating that it might be correlated to the presence of clay minerals. Regarding physical indices, it was found that the finer sediments have higher water contents and porosities but lower particle densities; total and dry. The coarser sediments present grains of spheroidal format, composed mainly of quartz, feldspar and amethyst.