Typhoon-induced suspended sediment dynamics in the mouth-bar region of a river/wave-dominated estuary

Abstract

Understanding suspended sediment processes in the mouth-bar region during typhoons is vital for estuarine geomorphic prediction and engineering design. An observation system was applied to explore suspended sediment dynamics during Typhoon Higos in the mouth-bar region of the river/wave-dominated Modaomen Estuary within the Pearl River Delta. The results showed that suspended sediment concentration (SSC) during typhoons could be around 30 times larger than that under normal conditions, primarily attributable to strong bed sediment resuspension induced by typhoon waves. The SSC captured during typhoon exhibited fluctuations of different amplitudes due to the movement of the high concentrated sediment in the mouth-bar region forced by the dominant flow. When the dominant flows were unified within the mouth-bar region in high velocities, including the wind-driven flow near the typhoon landfall and the ebb surge transport combined with the river flooding after landfall, the high concentrated sediment can move in a large distance along the dominant direction of the flow and induced dramatic decrease of SSC. When the dominant flows were not unified within the mouth-bar region and the velocities were relatively lower, the high concentrated sediment was dominated by the tidal process as under normal conditions and the SSC fluctuated in a smaller amplitude, including tidal modulation, flood dilution and ebb replenishment. Compared with the other estuary types, the processes controlling the storm-induced suspended sediment dynamics, including resuspension, wind-driven transportation and tidal transportation, all happened with high intensities in our surveyed river/wave-dominated estuary; and a conceptual model has been proposed to schematize these processes and their combined impacts.