Topographic Effects on Lagrangian Residual Flow in Stratified Estuaries

该项目的目标是更好地了解浅水河口产生的拉格朗日余流。粒子和溶质以拉格朗丹速度携带。因此，了解拉格朗丹速度的控制机制对于盐度和污染物分布的预测是非常重要的。层结和地形对拉格朗日余流都有很大的影响。由于强强迫河口的两层流处于近临界(洪水)或部分超临界(落潮)的内部水力状态，波长小于一个潮汐漂移的局部地形特征(如弯道、沙洲和洞穴)对等轴位移和垂直混合有很大的影响，从而对拉格朗日漂移有很大影响。因此，盐度和拉格朗日流量分布、垂直交换过程和河口地形都是密切相关的。这个为期三年的研究项目结合了对典型地形特征上流动的准确、小规模的现场测量与计算机建模，以确定基本的相互作用。该模型考虑了层状边界层和自由剪切层引起的湍流混合效应。

The goal of this project is to provide a better understanding of the Lagrangian residual flow generated in shallow estuaries. Particles and solutes are carried with the Lagrandain velocity. Therefore, knowledge of the controlling mechanisms of the Lagrandain velocity is esstenial for the prediction of salinity and pollutant distributions. Both stratification and topography have strong effects on the Lagrangian residual flow. Because the two-layer flow in a strongly forced estuary is in a nearly critical (flood) or partially supercritical (ebb) internal hydraulic state, local topographic features (e.g., bends, bars and holes) with wave lengths of less than one tidal excursion have a strong effect on isopycnal displacement and vertical mixing, and therefore on Lagrangian drifts. Thus, the salinity and Lagrangian flow distribution, vertical exchange processes and esturine topography are all closely related. This three-year research project combines accurate, small-scale field measurements of flow over typical topographic features with computer modeling to determine the essential interactions. The models include turbulent mixing effects caused by stratified boundary layers and free shear layers.