The effects of flocculation and bed erodibility on modeling cohesive sediment resuspension
The effects of flocculation and bed erodibility on modeling cohesive sediment resuspension
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DOI：
10.1029/2010jc006352
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发表时间：
2011-03
影响因子：
--
通讯作者：
M. Son;T. Hsu
中科院分区：
文献类型：
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作者：
M. Son;T. Hsu
絮凝作用和床层可蚀性是导致粘性沉积物输运比典型非粘性沉积物更为复杂的两个主要过程。早期的絮凝模型假定分形维数和/或絮凝体屈服强度恒定。然而，近年来的研究表明，考虑分形维数和絮体屈服强度为变量对于预测絮体粒径的时间演变至关重要。由于固结作用，泥浆层的临界床层剪切应力不能被参数化为常数。本研究进一步探讨了不同复杂程度的絮凝模型和河床可蚀性如何影响潮汐流驱动下产生的粘性沉积物再悬浮。修正了泥沙输移的一维垂直数值模型，加入絮凝和河床可蚀性两个模块。模型结果与Ems/Dollard河口实测数据进行了比较。模型研究表明，为了正确地模拟沉积物的供应，重要的是要考虑可变的临界剪切应力。当忽略絮凝作用或不完全考虑絮凝作用时，数值模型预测淡水期泥沙浓度接近于零，浓度梯度非常陡，与实测数据不一致。当分形维数和絮体屈服强度都是可变的时候，该数值模型预测的沉降速度要小得多，从而得到了与现场观测更为一致的混合状态。
[1] Flocculation and bed erodibility are two main processes causing the transport of cohesive sediments to be more complicated than typical noncohesive sediments. Earlier flocculation models assume a constant fractal dimension and/or a constant floc yield strength. However, recent studies have shown that considering both the fractal dimension and the floc yield strength to be variable is critical to the prediction of temporal evolution of floc size. Due to consolidation, it is also well established that critical bed shear stress of a mud bed cannot be parameterized as a constant. This study further investigates how flocculation models with different degrees of complexity and bed erodibility can affect the resulting cohesive sediment resuspension driven by tidal flows. A one-dimensional vertical numerical model for sediment transport is revised to incorporate modules for flocculation and bed erodibility. Model results are compared with data measured in the Ems/Dollard estuary. Model study suggests that it is important to incorporate variable critical shear stress in order to properly model the supply of sediment from the bed. When flocculation is neglected or incorporated incompletely, numerical model predicts nearly zero sediment concentration during slack water and very steep concentration gradient, which are inconsistent with the observed data. When the fractal dimension and the floc yield strength are both considered to be variable, the numerical model predicts much smaller settling velocity and hence captures the more well-mixed condition consistent with field observations.