Transport of riverine sediment from different outlets in the Pearl River Estuary during the wet season

Abstract

Riverine sediment is important for the development of river deltas and for carrying both nutrients and contaminants into estuaries and coasts. Previous studies of sediment transport have focused on single-sourced estuaries and paid less attention to multi-sourced estuaries (estuaries with multiple river discharge sources). In this study, we used the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modeling system to study the sediment transport in the Pearl River Estuary (PRE), where riverine sediments come from four different outlets. During a typical wet season (2007), about 6.8 million tons of riverine sediments were discharged into the PRE, most of which were trapped in shoals during neap tides, while about 11.8% by mass was transported out of the estuary during spring tides. The proportions of the multi-sourced sediments trapped in the PRE or escaping from the estuary depended on the morphology of the estuary and the location of the outlets in relation to the estuarine morphology. The distributions of different riverine sediments were mostly independent in neap tides but overlapped more in spring tides. The seaward sediment transport was dominated by river freshwater discharge in the upper estuary and by tidal forcing in the lower channels, while tides and winds controlled the sediment transport in the lower shoals. This study aids our understanding of sediment transport processes in multi-sourced estuaries and has implications for coastal environmental management.