基于机制分解法长江口南汇潮滩悬移质泥沙通量研究

FLUXES OF SUSPENDED SEDIMENT IN THE NANHUI TIDAL FLAT OF THE YANGTZE ESTUARY WITH MECHANISM DECOMPOSITION METHOD

基于实测资料以长江河口南汇潮滩为例,对传统机制分解法进行改进,将机制分解计算中的含沙量项按悬沙粒径进行分组处理,分为63～250、16～63、4～16、0.5～4μm 4个粒径组,对各粒径组泥沙的净输移通量分别进行机制分解计算,分析不同粒径组泥沙的各机制分解项对悬沙净输移通量的贡献。研究表明不同粒级的泥沙其控制输沙的潮滩动力因子不同。相当于粘土类(0.5～3.9μm)和细粉砂类(3.9～16μm)粒级的悬移质泥沙,平均流项T1+T2及潮泵项T3+T4+T5对其输移起控制作用;相当于粗粉砂类(16～62.5μm)和细砂类(62.5～250μm)粒级的悬移质泥沙,潮泵项T3～T5、潮振荡项T6～T8起控制作用。同时,对不同水深条件下同粒级悬沙净输移通量的机制分解项的比较,当悬沙输移过程由深水进入浅水时,潮泵项的贡献急剧减小,且不受大小潮汛、悬沙颗粒粒级粗细的影响。

Based on the mechanism decomposition method,mechanisms of sediment transport in Nanhui tidal flat have been assessed with field data.The traditional mechanism decomposition method was improved in this study by dividing the suspended sediment into 4 groups（62.5~250μm,16~62.5μm,3.9~16μm,0.5~3.9μm） according to the grain size and analyzing each group separately.The results reveal that the transport of suspended sediment of different groups was controlled by different mechanisms.The transport of clay and fine silt was controlled by advection terms and tidal pumping terms.With respect to the transport of coarse silt and fine sand,tidal pumping terms and shear diffusion terms caused by the variation in the form of the vertical profiles of velocity and suspended sediment concentration both played main roles.Meanwhile,by comparing the main mechanisms contributing to the sediment transport of the same group in different water depths,it is found that the contribution of tidal pumping terms decreased sharply when suspended sediment was transported from deepwater area to shallow water area,and the trend didn＇t change with the variation in the tide type and grain size.