A mecânica do transporte de sedimentos em suspensão no estuário do rio Macuse, Moçambique, Sudeste De África

Abstract

This manuscript study’s the mechanics of suspended sediment transport in Macuse Estuary River in Mozambique, East Africa. The methodological approach was based on geomorphologic and oceanographic surveys covering 42 georeferenced stations. We conducted in situ tide and current measurements with a RBRduo tidal gauge and current-meter moored at the Macuse Harbour. The fieldwork comprised data collection in two periods, from 17th to 19th November 2013 and from 16th to 21st November 2014. Water samples were collected in a Niskin bottle for suspended sediment analysis. The sediments were filtered using a 47?m fiberglass and a vacuum pump, which were weighted in a highly precise electronic scale. Hydrodynamic simulations were conducted using a three-dimensional numerical model with the ELCOM-CAEDYM covering the period of in situ data collection. The calibration and validation of simulated results were performed through comparisons of field data and the simulated results. The in situ and modeled results indicated tides of 4.0 m in height that generated tidal currents between -0.8 m/s and 1.2 m/s. Its cyclic hydrodynamic regime defined the mechanics of sediment transport in suspension of the silt and fine sand group by dragging process. The concentrations of silt and very fine sand obtained through the implementation of the ELCOM-CAEDYM model indicated fractions between ~ 100 mg/l and ~ 300 mg/l during the ebb and flood tides. These concentrations suggest sedimentation in the riverbed by silt with a flow of less than 0,1 cm/s and of very fine sand with a flow of less than 10 cm/s. The sedimentation in the bed can occur by very fine sand fractions that may cause significant modifications in the geomorphological configuration of the Macuse Estuary River and technical port operations.