Tidal impact on suspended sediments in the Macuse estuary in Mozambique

Many studies around the world have found that tidal dynamics control the transport of suspended sediments in estuaries, as well as their relationship with runoff discharges and bathymetry morphology. This manuscript examines tidal impact on suspended sediments in the Macuse estuary in Mozambique, southern Africa. Data was collected at 42 stations, including tidal current measurements with an Acoustic Doppler Current Profiler (ADCP), tide elevation with a tidal gauge and suspended sediments with a Niskin bottle. A 14-month model simulation was implemented beginning in November 2013, forced by tides, wind regime and runoff discharges. The results indicated a tidal elevation of 4 m that generated tidal currents of 120 cm s−1. These currents combined with the runoff of 500 m3 s−1 and bathymetry configuration, drove the suspended sediments during the ebb and flood tides. Suspended sediment concentrations suggested the occurrence of sedimentation where water flow was less than 0.10 cm s−1for silt and less than 10 cm s−1 for fine sand. Results of silt concentrations was about ∼ 300 mg l−1 while fine sand was found to be 0.2 mg l−1in both tidal periods in ebb and flood tides during the rainy and dry seasons. The model accuracy of about R2 = 0.88 between the observed and simulated results demonstrated the ability to predict the impact of tides and runoff discharges in the Macuse estuary and may be extended to other estuaries. The model matches in reproducing the sediment transport mechanism will help making political decisions about the estuary sustainability and local coastal management.