长江口北槽近底高质量浓度泥沙形成关键机制分析

Analysis on Key Mechanisms of Formation of Near-bed High-Concentration Sediment Suspension Within the North Passage of the Changjiang Estuary

通过对长江口北槽水文泥沙观测数据的分析,并结合前人的研究成果,定性地确定了制约沉降及紊动抑制作用在长江口近底高质量浓度悬浮泥沙的形成中有重要的作用;通过一个基于FVCOM的一维垂向泥沙模型定量地确定了制约沉降对水体含沙量浓度的增加作用,但紊动抑制显著地改变了泥沙浓度的垂向结构,增强了近底层的水体层化,从而形成了较为明显的近底高质量浓度泥沙悬浮;与实测数据的对比结果显示,制约沉降与紊动抑制作用的联合作用对近底高质量浓度悬浮泥沙模拟结果有显著的改善作用,模型能够较好地模拟大潮期间的长江口近底高质量浓度泥沙垂向剖面过程。

Based on the theory of sediment dynamics,the observed data for hydrodynamics and sediment from the Changjiang Estuary was analyzed.The results indicated that the hindered settling and turbulence suppression were two major physical mechanisms in the formation of the near-bed high-concentration sediment suspension in the Changjiang Estuary.A one-dimensional vertical(1DV)sediment model,under the quasi-realistic tidal forcing,was used to quantitatively determine the contribution of these two major mechanisms.The comparison between simulated and observed data showed that both of hindered settling and turbulent suppression could increase the near-bed suspended sediment concentration,and yet the latter mechanism could significantly produce vertical sediment stratification and near-bed high-concentration.The 1DV model with the inclusion of joint effects of these two physical dynamics could resolve the vertical structures of suspended sediment concentration in the North Passage during the spring tide cycle.