In the northwestern South China Sea (SCS), highly coupled wave–current dynamics create complex sediment transport patterns that challenge marine engineering. This study integrates multi-source datasets of waves, tides, and sediments with transport modeling to analyze sedimentary responses and multiphase transport under monsoon–tide interaction. Results reveal a source–dynamics coupling mechanism: the northern silt zone shows strong positive skewness, suggesting coarse particle retention, while the central-southern sandy transition zone features a high–low–high sorting pattern, indicative of non-steady sorting under variable energy. Bedload transport exhibits a tidal energy hierarchy (spring > mean > neap), with flood-dominant transport in the fine-sand zone (critical shear stress: 0.283 N/m2) and episodic spring-tide transport in the coarse-sand zone (>2.2 N/m2), demonstrating that the spatial variability of critical shear stress provides a useful indicator of seabed stability and scour sensitivity. Suspended sediment stratifies during spring tides but homogenizes during neap tides. Transport direction shifts from southwestward to southeastward across tidal regimes. A counterclockwise residual circulation drives bidirectional sediment migration, with nearshore suspended loads converging and offshore bedload diverging. Wind-driven currents during neap tides promote offshore sediment export. In the bedload-suspended sediment multiphase transport, suspended sediment transport plays a dominant role and is the primary source of sediment spatial transport in the study area. This study quantitatively reveals multiphase sediment transport mechanisms, advancing understanding of continental shelf sedimentary–morphodynamic processes and seabed stability.
Botao et al. (Fri,) studied this question.