Water discharge and sediment load to Sepetiba bay from an anthropogenically-altered drainage basin, SE Brazil.

Abstract

mpirical relationships coupled with the field measurements were used to assess water discharge and sediment load from an anthropogenically-altered drainage basin into Sepetiba Bay in southeastern Brazil. Discharge into Sepetiba Bay is modified by large-scale water diversion from the Paraíba do Sul River, which is one of the more important and impacted rivers in Brazil. The discharge into Sepetiba Bay has increased threefold, from 41 to 129 m3/s on average, since the water redistribution began. Sediment budget calculations indicate retention of a large fraction of the sediment load by five reservoirs within the drainage system but with highly variable infilling rates. As a consequence the water diversion scheme has lead to a 28% increase in sediment delivery to Sepetiba Bay or 270 × 103 t/yr. The Paraíba do Sul River contributes most of the freshwater input into Sepetiba Bay, whereas the sediment load to the bay is mainly contributed by the local drainage basins.