Seasonal Variations in Riverine Sediment Transport Timescales in the Pearl River Estuary

Understanding sediment transport timescales is essential for predicting morphological evolution, pollutant accumulation, and ecosystem health in estuaries. This study examines seasonal hydrodynamics and sediment transport in the Pearl River Estuary using a well-calibrated numerical model. The results indicate that plume dynamics largely control sediment transport in both the wet and dry seasons. During the wet season, sediments are exported along both estuary flanks with the expanding freshwater plume. Under the combined effects of topography and the Coriolis force, a greater proportion of sediments exits via the confluence of the West Channel and West Shoal. In the dry season, prevailing northeasterly winds suppress sediment export along the East Channel, redirecting most of the riverine sediment westward. Sediment transport timescales, quantified by sediment age, further show that, during the wet season, export via the East Channel requires approximately 30 days, whereas export along the western flank takes about 45 days due to the weaker dynamics over the West Shoal. Reduced river discharge in the dry season increases sediment age overall; offshore delivery within the plume region takes roughly 50 days, while transport via the East Channel may require an additional 30–60 days. Comparative simulations with and without wind forcing reveal that southerly winds during the wet season weaken plume intensity and prolong transport timescales, whereas northeasterly winds in the dry season enhance plume dynamics, accelerating sediment export from the estuary. Collectively, these findings clarify the mechanisms underlying the seasonal variability in sediment transport and provide a scientific basis for estuarine management and engineering.