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首页> 外文期刊>Ocean Dynamics >Effects of bottom slope, flocculation and hindered settling on the coupled dynamics of currents and suspended sediment in highly turbid estuaries, a simple model
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Effects of bottom slope, flocculation and hindered settling on the coupled dynamics of currents and suspended sediment in highly turbid estuaries, a simple model

机译：一个简单模型，底部坡度，絮凝和受阻沉降对高浊度河口水流和悬浮泥沙耦合动力学的影响

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This study aims at gaining basic understanding about two specific phenomena that are observed in the highly turbid estuaries tidal Ouse, Yangtze and Ems, i.e. (1) the accumulation of suspended matter in the deeper parts of the estuaries and (2) the relatively high values of turbidity near the surface in the area of the turbidity maximum. A semi-analytical model is analysed to verify the hypothesis that these phenomena result from bottom slope-induced turbidity currents and from hindered settling, respectively. The model governs the dynamics of residual flow, driven by fresh water discharge, salinity gradients and turbidity gradients. It further uses the condition of morphodynamic equilibrium (no divergence of net sediment transport) to compute the residual sediment concentration. New aspects are that depth variations on flow and mixing processes, as well as flocculation and hindered settling of sediment, are explicitly accounted for. Tides act as a source of mixing and erosion of sediment only, thus processes like tidal pumping are not considered. Model results show that the estuarine turbidity maximum (ETM) shifts in the down-slope direction, compared to the case of a constant depth. Slope-induced turbidity currents, which are directed down-slope near the bottom and up-slope near the surface, are responsible for this shift, thereby confirming the first part of the hypothesis above. The down-slope shift of the ETM is reduced by currents resulting from gradients in depth-dependent mixing, which counteract turbidity currents, but which are always weaker. Including flocculation and hindered settling yields increased surface sediment concentrations in the area of the turbidity maximum, compared to the situation of a constant settling velocity, thereby supporting the second part of the hypothesis. Sensitivity experiments reveal that the conclusions are not sensitive to the values of the model parameters.
机译：这项研究旨在获得对在高浑浊的河口潮汐乌兹河，扬子和埃姆斯河中观察到的两个特定现象的基本理解，即（1）河口较深部分的悬浮物积累和（2）相对较高的值。在最大浊度区域的表面附近的浊度。对半分析模型进行了分析，以验证以下假设：这些现象分别是由底坡引起的浊流和阻碍沉降的结果。该模型控制着由淡水排放，盐度梯度和浊度梯度驱动的剩余流动力学。它还使用形态动力学平衡的条件（净沉积物传输没有差异）来计算残余沉积物浓度。新的方面是明确考虑了流动和混合过程中的深度变化以及絮凝和沉积物的阻碍沉降。潮汐仅起沉积物的混合和侵蚀的作用，因此不考虑潮汐抽水等过程。模型结果表明，与恒定深度的情况相比，河口浊度最大值（ETM）在向下倾斜的方向上移动。斜率引起的浑浊流是造成这种偏移的原因，该浊流指向底部附近的下坡和表面附近的上坡，从而证实了上述假设的第一部分。 ETM的下坡偏移通过深度相关混合的梯度所产生的电流而减小，这抵消了浊度电流，但始终较弱。与恒定沉降速度的情况相比，包括絮凝和沉降沉降的产生，在最大浊度区域增加了表面沉积物的浓度，从而支持了假设的第二部分。敏感性实验表明，结论对模型参数的值不敏感。

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