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首页> 外文期刊>Estuarine Coastal and Shelf Science >Simulating high ebb currents in the North Passage of the Yangtze estuary using a vertical 1-D model
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Simulating high ebb currents in the North Passage of the Yangtze estuary using a vertical 1-D model

机译：使用垂直一维模型模拟长江口北通道的高退潮电流

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摘要

A strong maximum ebb current (> 3 m/s) in the upper water column was observed at Station CS3 in the middle of the North Passage of the Yangtze River Estuary during the wet season, which was higher than either its upstream or downstream counterparts. To better understand the mechanisms and factors causing the strong ebb current, a vertical one-dimensional (1-D) model was used to conduct a diagnostic study. The model used time series of observed tidal amplitudes, vertical salinity, and suspended sediment concentration (SSC) profiles to compute the density and turbulence. Two tunable parameters, the tidal amplitude attenuation coefficient (i.e., the phase lag) and the background surface pressure gradient that represents the net pressure gradient induced by the freshwater discharge and baroclinic effect, were used to determine the best match with the observed high velocity amplitudes in addition to the bottom roughness height. Three hypotheses of possible causes are tested: (1) the large freshwater discharge, (2) the bottom stratification effects (which were caused by a possible high near-bed suspended sediment gradient), and (3) the unique location of the CS3 station that was influenced by local geometry. The findings show that neither of the first two factors has much influence on the pronounced ebb velocities. Instead, the energy loss caused by the change of channel geometry and a maximum convex bathymetry in the North Passage of the Yangtze River Estuary are the main reasons behind the extremely high observed ebb current velocity profiles. The high near-bottom SSC and gradient located within 0.5 m above the bed only slightly alters the velocity profiles. This 1-D model is convenient for testing a different hypothesis and for coupling with other selected variables to account for the floc size distributions in future studies. (C) 2017 Elsevier Ltd. All rights reserved.
机译：在雨季期间，长江口北通道中段CS3站的上水柱观测到了强烈的最大退潮电流（> 3 m / s），高于其上游或下游同行。为了更好地理解引起强烈退潮的机制和因素，使用垂直一维（1-D）模型进行诊断研究。该模型使用观测到的潮汐振幅，垂直盐度和悬浮沉积物浓度（SSC）剖面的时间序列来计算密度和湍流。潮汐振幅衰减系数（即相位滞后）和代表由淡水排放和斜压效应引起的净压力梯度的背景表面压力梯度这两个可调参数被用来确定与观测到的高速振幅的最佳匹配。除了底部粗糙度的高度。测试了三个可能的原因假说：（1）大量淡水排放；（2）底部分层效应（这是由于可能存在的高近床悬浮沉积物梯度所致）；以及（3）CS3站的独特位置受局部几何形状的影响。研究结果表明，前两个因素均未对明显的落潮速度产生太大影响。取而代之的是，由长江河口北通道的航道几何形状变化和最大凸测深所引起的能量损失是观测到的高退潮流速剖面的主要原因。位于床上方0.5 m内的高近底部SSC和坡度仅会稍微改变速度剖面。这种一维模型可方便地测试不同的假设，并与其他选定变量耦合以考虑将来研究中的絮体尺寸分布。 （C）2017 Elsevier Ltd.保留所有权利。

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