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Flood-ebb asymmetry in current velocity and suspended sediment transport in the Changjiang Estuary

查看全文 作　　者：LI [1]Zhanhai;WANG [2]Yaping;CHENG [3]Peng;ZHANG [1]Guoan;LI [1]Jiufa 高影响力作者 机构地区：[1]State Key Laboratory of Estuarine and Coastal Research, East China Normal University;[2]School of Geographic and Oceanographic Sciences, Nanjing University;[3]College of Ocean and Earth Sciences, Xiamen University高影响力机构 出　　处：《Acta Oceanologica Sinica》索引2016年第35卷第10期,共11页高影响力期刊 基　　金：The National Natural Science Foundation of China under contract Nos 41176069 and 48505350;the Major State Basic Research Development Program of China under contract No.2013CB956502 摘　　要：Time series measurements were conducted on suspended sediment and current velocity from neap tide to spring tide in the South Branch of the upper Changjiang Estuary in the summer of 2011. Strong flood-ebb asymmetry in the current velocity was observed in the South Branch as a result of high river runoff and tide deformation, in which the magnitude and duration of ebb currents were significantly greater than those of flood currents. The suspended sediment concentration(SSC) and suspended median grain size also exhibited remarkable flood-ebb variation; these variables were considerably larger during the ebb than during the flood and increased from neap to spring tide. Affected by the strong asymmetry in the current velocity and SSC between the flood and ebb,suspended sediment flux during the ebb was notably larger than during the flood, and a seaward tidal net flux was observed in each tidal cycle. The balance of sediment flux illustrates that the seaward sediment transport was dominated by river flow and tidal trapping and the landward sediment transport was dominated by the Stokes drift and the shear effect. Notable resuspension occurred during the spring and moderate tides. The critical velocity for the resuspension of bed sediments was estimated based on the correlation between current velocity with SSC and suspended median grain size. The results show that the critical velocity was approximately 40 cm/s during the flood phases and approximately 80 cm/s during the ebb phases because the surficial flood bed sediments located in the lower reach are much finer than the surficial ebb bed sediments located in the upper reach. The flood-ebb variation in the critical erosion velocity has significant effect on the intratidal variation of SSC and sediment transport process, and it is a common phenomenon in many estuaries of the world due to the complicated spatial distribution of bed sediments. 关 键 词：洪水涨落 水流速度 不对称性 悬沙输运 悬浮泥沙浓度 长江口 沉积物再悬浮 电流速度
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