长江河口悬沙与盐分输运机制分析  

Analysis of the transportation mechanism of suspended sediment and salt in the Changjiang River Estuary

作　　者：吴祥柏[1] 汪亚平[1] 潘少明[1] 

机构地区：[1]南京大学海岸与海岛开发教育部重点实验室

出　　处：《海洋学研究》2008年第4期8-19,共12页Journal of Marine Sciences

基　　金：国家自然科学基金资助项目(40106009);国家重点基础研究发展规划资助项目(2002CB412401)

摘　　要：2004年9月15～22日在长江口南支口门区域进行了水位、流速、悬沙浓度、盐度的全潮观测，基于这些现场数据，分析河口区域流速结构、悬沙浓度与盐度的时空分布特征；利用机制分解法研究河口悬沙、盐分的通量和输运机制，并探讨它们与水体垂向结构之间的关系。主要结论如下：长江河口区的悬沙浓度存在显著的时空变化特征，从口内向口外，悬沙浓度呈显著减小趋势，大潮期间的悬沙浓度较大，是小潮期间的数倍。通量机制分析结果表明，长江河口区以欧拉余流为主，向海输运，并有向海方向逐渐减小的趋势，斯托克斯余流向陆输运，在大、小潮期间有显著差异。盐分输运机制中，以欧拉余流占主导地位，潮泵效应、垂向重力环流、垂向剪切扩散作用的贡献次之。长江河口悬沙净输运率在向海方向逐渐减小，大潮期间的悬沙净输运率比小潮期间的大1～2个数量级，水动力条件是造成长江河口悬沙净输运时空差异的主要因素。悬沙输运机制小潮期间以欧拉余流占主导地位，在大潮期间则以与紊流相关的垂向剪切扩散作用取代欧拉余流占据主导地位。悬沙瞬时输运机制中的剪切扩散项在中下层水体的理查德森数（Ri）小于0．25时才有较大的量值，在南槽内，当底层水体的理查德森数（Ri）处于0．1％Ri〈0．25范围时，剪切扩散贡献值的大小与Ri之间存在显著的负相关关系。研究还表明，适当的紊动强度有利于高悬沙浓度的维持，区域性的层化作用对紊流有强烈的抑制作用，这是造成长江河口悬沙输运空间差异的主要因素之一。In recent years, the construction or operation of some major projects, such as the South-to-North Water Diversion Project, Three Gorges Dam, the Reclamation Project in East Hengsha Shoal and Deep Channel Regulation Project in the Changjiang River Estuary, would have a profound impact on the physical processes in the Changjiang River Estuary. Monitor and study of the mass fluxes and their mechanism have great significance on the construction of the projects and exploitation of natural resources. Based on the measurements of the water level, current speed and direction and suspended sediment concentrations （SSC） at four stations located in the outlet area of the Southern Branch in the Changjiang River Estuary during both spring and neap tides on 15-22 September 2004, the temporal and spatial distributions of the velocity structure, SSC and salinity of the water column were analyzed, and the fluxes of the suspended silt and salt and their transport mechanisms were studied with flux decomposition method. The relationship between mass flux mechanism and vertical structure of the water column were also discussed. Research shows that the SSC in Changjiang River Estuary has significant temporal and spatial changes： it reduced significantly from the mouth to the sea, and it was several times greater in spring tide than that in neap tide. Flux mechanism analysis shows that the dominant factor for water transport in the Changjiang River Estuary is the Eulerian residual flow. It transports water towards to the sea, in the opposite direction of Stokes drift. For the transport of salt, Eulerian flow plays the leading part and the next is the tidal pumping, vertical gravity circulation and dispersion due to vertical shear stress. Net transport of suspended silt decreases seaward. Net transport in spring tide is greater than that in neap tides with an order of magnitude of one to two and the hydrodynamic condition is the major factor for the temporal and spatial difference. During neap tide Eulerian residual flow

关 键 词：悬沙浓度 盐分输运 理查德森数 通量分解 长江河口 

分 类 号：TV148.1[水利工程—水力学及河流动力学]