【作者】 王元叶；

【导师】 何青；

【作者基本信息】 华东师范大学 ， 自然地理学， 2004， 硕士

【摘要】 近底水沙垂向混合运动，在河口产生变异而造成水沙垂向分布的不连续性，是河口海岸泥沙运动的重要特点和研究的难点。河口底部边界层和细颗粒泥沙过程是海洋学家、港口航道与海岸工程师和环境流体力学乃至生物地球化学研究人员共同感兴趣的研究课题。长期以来，长江河口水沙运动规律的研究都基于常规“六点法”取得的水文观测资料，而对近底床面层水沙运动资料的获取和规律分析尚不多见。因此，以长江口为主要研究区域，研究其垂向乃至近底水流结构特征和泥沙交换过程具有重要的理论意义，对港口选址、航道治理、河口综合开发和整治都具有极为重要的应用价值。 ■ 高频声学多普勒流速剖面仪近底有效单元数据提取 本文首先对近底边界层(Bottom Boundary Layer,BBL)数据获取方法和观测仪器进行了总结。在当前野外观测条件下，应用了海流计近底加密观测法和船载高频声学多普勒流速剖面仪((?)coustic(?)oppler Current (?)rofiler，ADP)近底流速观测法，进行垂向和近底流速的观洲。通过分析声强垂向剖面分布的特征，利用数学极值定理，确定了床面位置，进而将ADP处理软件“丢弃”的那部分近底流速数据或由于底跟踪丢失而损失的流速数据提取出来。利用同步“六点法”电磁海流计所得到的最底层流速数据对提取出来的ADP近底单元数据进行验证。结果表明提取出来的那部分ADP近底流速数据是可用的。 ■ 近底边界层结构 近底边界层的研究主要侧重于流速垂向分布和动力特征(摩阻流速、糙率长度)及悬浮泥沙浓度垂向分布。流速的垂向分析结果表明：流速垂向结构可以分为三段，即上段、中段和下段。这种分段是由水流和外边界阻力共同作用产生的结果。憩流期阶段或低流速阶段，垂向流速分布不尽符合对数流速分布。非憩流阶段，在观测站点(徐六泾和七丫口)流速垂向分布基本上符合对数流速分布。近底流速垂向分布要比流速垂向分布更符合对数流速分布，它们普遍符合对数分布。 从流速结构的角度出发，得到了两类不同的BBL厚度变化。一类是BBL厚度随水深变化没有规律性趋势，另一类BBL厚度随水深变化过程呈正相关。但是，这两类BBL厚度随流速大小的变华东师范大学硕士伦久长江。近底边界层魂侧研究化都出现了相应的变化。前者和流速变化关系为止相关，后者为负相关。对两类BBL厚度的成因分 心廿从调析表明，BBL厚度所旱现出的不同的变化规律是由底形作用和动力作用(土要是径、潮流作用)相的综合结果。 底部剪切应力或摩阻流速是影响泥沙运动的关键参数。近底动力参数的分析结果表明:摩阻流速和流速的关系为正相关，而糙率长度和流速的关系为负相关。徐六径和七’‘口两个测站所得到的摩阻流速变化范围分别为1.82一14.71c耐S和0.71一11.41c耐S:糙率长度变化范围分别为002一26.20cm不1 1 0.04一16.49em。 ，悬浮泥沙浓度垂向分布的分析结果表明在一个潮周期内悬浮泥沙浓度垂向结构将出现不同的刑式。在憩流期及其前后SSC垂向分布呈“L’，型分布:随着涨、落潮过程，悬沙浓度的垂向结构发生有规律的变化，即中上层悬沙浓度逐渐增人，垂向结构由憩流期的“U，型分布逐渐过渡到指数分布:涨、落急及其前后流速较人，悬沙浓度垂向分布趋于更加均匀，表层和底层悬沙浓度差别逐渐变小:涨落潮变化过程中，由于悬浮泥沙沉降起动及垂向的掺混作用，悬沙浓度垂向分布发生调整，表现为悬沙浓度垂向梯度的变化。本文对Rouse公式在长江口的适用条件也进行了分析。结果表明，在落急及其前后时段，水流速度持续较人且较稳定的情况卜，Rouse公式能够较好的反映悬浮泥沙浓度垂向分布。在该时段内，采用Rouse公式拟合求解得到的悬沙沉降速度为0.19~o.24cl布S，平均为O.ZO5c耐S;而在涨潮过程及憩流前后，由于流速变化较大，没有一段持续较稳定的流速过程，Rouse公式不能够很好反映悬浮泥沙浓度垂向分布。在基本满足即落急及其前后时段，利用表层实测悬沙浓度值为参考浓度能够得应用的水动力条件卜，底层悬浮泥沙浓度为参考浓度同样好的结果。这一认识为人面积利用遥感资料反演泥沙浓度场及相关研究提供了可用的依据。更多还原

【Abstract】 The variations that are produced by the mixing of fluid and sediment of near bed lead to the discontinuity of velocity distribution and suspended sediment concentration distribution, which is an important and difficult aspect for the research on estuarine and coastal sediment transport. The bottom boundary layer (BBL) refers to those portions of sediment column and water column which are influenced directly by the presence of the sediment-water on the distribution of their properties and processes. It is the very zone of great importance to the biology, chemistry, geology and physics in the oceans, seas, lakes even rivers, and it is also a transportation intensive zone in both of vertical and lateral sides for the solutes and (re)suspended particles, while the reactivity of chemical and biological materials are quite strong as well . Both of the estuarine bottom boundary layer and cohesive fine sediment transport processes interest the oceanographer, engineers of port, environmental hydrodynamics and biogeochemistry researchers.For a long time, the data for researching the mechanics of fluid and sediment transport are mainly from regular hydrology geology investigations. However, the data near the bed are limited and the results about the mechanics of the water-sediment movement near the bed are also in deficiency. The exchange between the suspended sediment and bed load occurs frequently in Changjiang estuary, which is a typical mesotidal one. Therefore, there is a great theoretic significance to research the vertical velocity characteristics and the processes of sediment exchange, even of the near bed region. These jobs can make up the disadvantage in the estuarine and coastal science research and enrich the contents of hydrodynamics and sediment transport. They also have very important applied value in the selection of port site, regulation of navigation channel, integrated development and management for estuary etc. Data acquirement of valid cells of 1.5 MHz ADP near bedThis paper firstly gives a brief introduction to the data aquirement methods and the observation instruments. The author proposes two new methods to measure the velocity near bed, which are velocity measurement near bed with small distance by electric current meter and velocity measurement near bed with mounted ADP with high frequency, respectively. Then, the paper gives an instruction in detail on thedata acquirement of valid cells of ADP near bed. According to the analysis of the vertical distribution of signal amplitude with using extremum theorem, the location of the bed is fixed and the velocity data are extracted which once lost due to the disadvantage of ADP software and the errors of bottom track algorithm. The validity of the extracted data is verified by using the synchronous data with the same depth of electric current meter. The structure of BBLThe researches of BBL mainly set focus on the vertical structure (vertical distribution of velocity and suspended sediment concentration) and dynamics characteristics (shear friction velocity and roughness length) in BBL. The analytical results of vertical distribution of velocity show that: the vertical structure of velocity can be divided into three sections, i.e. upper section, middle section and bottom section. Such vertical distribution of velocity is caused by the interaction between the current and the outside force or resistance; the vertical distribution of velocity at the observation stations (one is Xuliujing and another is Qiyakou) doesn’t correspond with the log-distribution velocity formula during the slack water or the period with low current speed; the whole profile distribution of velocity accords with the log-distribution velocity formula during the non-slack water; and the distribution of velocity near bed is more accordant with the log-distribution velocity formula than that of the whole velocity profile.From the velocity vertical structure perspective, two types of variations of the thickness of BBL are obtained. One type is that the thickness of BBL do更多还原