珠江口洪季斜压作用对悬沙浓度与输运的影响

Impacts of baroclinic effects on suspended sediment concentration and transport in the Pearl River Estuary during the wet season

中文关键词:  斜压作用  悬沙浓度  COAWST海洋模式  珠江口

英文关键词:baroclinic effects  suspended sediment concentration  COAWST modelling system  The Pearl River estuary

中文摘要:

      珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响，其中斜压效应不可忽视。本文采用 Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System （COAWST） 海洋模型系统，以 2022年6月份 （洪季） 的珠江口为例，研究斜压效应对悬沙浓度分布与输运通量的影响。采用控制实验，研究有无斜压作用时悬沙浓度分布的变化；分析有无斜压作用时的泥沙输运通量与海底冲淤的变化情况，结果表明有斜压作用时悬浮泥沙的输运路径、通量均与无斜压时不同，伶仃洋的悬沙除向西口外输运外，还随着河口羽流的扩展向西南方向输运。有斜压作用时在伶仃洋的西南端及下游的西南沿岸均有明显的海底淤积，而无斜压作用时泥沙淤积主要发生于伶仃洋的西口附近及磨刀门口外落潮射流末端。利用悬沙输运方程进行诊断分析，揭示了斜压作用导致悬沙浓度分布与输运通量变化的动力机制，表明斜压作用虽然减小了底切应力与垂 向混合系数，但由于增大的海底泥沙可侵蚀量及垂向悬沙梯度，悬沙输运方程中的再悬浮量与垂向混合通量要比无斜压时要大。本研究对河口区的悬沙输运过程与机理分析具有一定的指导意义。

英文摘要:

      The distribution and transport flux of suspended sediment in the Pearl River Estuary are influenced by multiple factors, among which baroclinic effects should not be overlooked. In this study, we utilize the COAWST modelling system, and take June 2022 as an example to investigate the impacts of baroclinic effects. Through controlled experiments, we examine the variations in suspended sediment concentration, and analyze changes in sediment transport flux as well as seabed deposition and erosion caused baroclinic effects. The results show that baroclinic effects alter both sediment transport pathways and fluxes. In addition to sediment export from the west entrance of the Lingding Bay, another pathway emerges along the plume-spreading trajectory induced by river plume formation. By analyzing changes in terms in the sediment transport equation, we conduct a diagnosis analysis, and reveal the mechanisms driven by baroclinic effects. The findings indicate that although baroclinic forces reduce bottom stress and vertical diffusivity, they enhance bottom resuspension and vertical diffusion by increasing sediment availability at the bottom and the vertical gradient of sediment concentration. This study contributes to a better understanding of sediment transport and its associated dynamics.