| 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...
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