河口混合与泥沙输运

MIXING AND SEDIMENT TRANSPORT IN ESTUARIES

根据振荡边界层理论和波流分解方法，导出了河口往复水流的流速垂向分布廓线，据此建立了河口垂向准二维水流、盐度、泥沙运动模型．对泥沙输运，完整地考虑了其对流、扩散、起动和沉降的动力学过程．模拟结果与实测资料进行了对比．应用该模型研究河口泥沙输运，分析了河口混合对泥沙输运的影响及最大浑浊带的时空变化规律．

To simulate estuarine flow and transport of salinity and sediment, a quasi-2D mathematical model is proposed on the basis of the oscillatory boundary layer theory and component decomposition approach. The influences of fresh and salt water mixing on sediment transport and the spatial and temporal variations of maximum turbidity are addressed. To begin with, the difference of vertical velocity profiles between oscillatory and unidirectional flow is analyzed by accounting for characteristics of estuarine flow. And thus the mean velocity is decomposed into runoff and tide components at first. Subsequently, a theoretical expression for vertical velocity profile in terms of its depth average is derived by applying the universal logarithmic law and oscillatory boundary layer theory. The derived expression is then used to establish a qusi-2D model to simulate sediment transport in estuaries. For sediment transport, the model is focused on the dynamic processes, such as convection, diffusion, suspension and settling. It simultaneously models flow pattern, salinity distribution and sediment concentration field. In particular, turbulent bursting effect is considered to construct a reasonable pick--up function for estimating sediment suspension flux at the bottom. The influence of compact process of bed material on the incipience and the flocculation settling process in salty water are accounted for as well. The model is validated by field data and proved advantageous in more physical implications and less CPU time demand. By case studies, we have finally obtained the dependence of sediment concentration on mixing indices and sediment supply from upstream river. And the formation of maximum turbidity and its shifting with mixing indices and tidal phases are also discussed.