River morphodynamics and its mathematical modelling

这项研究计划将冲积河流河床和河岸变形所涉及的水沙运动机理的理论和试验研究与开发基于物理的高精度数值模型相结合，用于模拟和预测河流形态变化。这些变化可能是自然发生的，也可能是对人类河流直接或间接干预的反应。这项研究的重点是：1-大尺度湍流相干结构及其形态后果；以及蜿蜒溪流中的两床形态变化和岸滩迁移。据介绍，将在一条20米长、宽度从1米到2米可调的直槽中进行一系列广泛的实验。在这些实验中，将记录大规模相干结构的产生、生长和衰变事件及其形态后果。这项研究有望更好地了解大规模河床形态(交替和多个沙洲)的发展，以及河流初期偏离直线走向最终导致蜿蜒或辫状的发展。此外，还将研究蜿蜒溪流中涉及河床和河岸变形的水流和泥沙输送机制。为此，位于21米长、7米宽的沙盆上的初始(非平衡)实验室曲折河流将受到各种水流条件的影响，并将对其时间演变进行监测。新的数据和见解将被用来开发两个数值模式：(I)一个基于三维的模型，用于计算曲折河床地形及其时间演化；(Ii)一个模型，用于模拟曲流的长期平面演变和预测曲流迁移速率。这些模型有望成为评估自然和人为曲折形态变化对物理环境影响的有价值的工具。他们表示，这项研究计划将培养3名博士生，3名硕士研究生。学生和1名理科学生。

This research program combines the theoretical and experimental research of mechanisms of flow and sediment transport involved in the deformation of bed and banks of alluvial streams with the development of physically-based, high-accuracy numerical models for the simulation and prediction of river morphological changes. These changes may occur naturally or as a response to direct or indirect human river interventions. The research focuses on: 1- large-scale turbulence coherent structures and their morphological consequences; and 2- bed morphological changes and bank migration in meandering streams.       An extensive series of experiments will be carried out in a 20m-long straight channel having an adjustable width from 1m to 2m. In these experiments, events of generation, growth and decay of large-scale coherent structures and their morphological consequences will be recorded. This study is expected to yield a better understanding of the development of large-scale bed forms (alternate and multiple bars) and the development of incipient stream deviations from straight alignment eventually leading to meandering or braiding. It will also constitute a foundation for the future modelling of these processes.       Additionally, the mechanisms of flow and sediment transport involved in bed and bank deformation in meandering streams will be investigated. For this purpose, initial (non-equilibrium) laboratory meandering streams lying on a 21m-long, 7m-wide sand basin, will be subjected to a variety of flow conditions and their time-evolution will be monitored. The new data and insights will be used to develop two numerical models:(i) a 3-D based model for the computation of meandering bed topography and its time-evolution; and (ii) a model for the simulation of the long-term planimetric evolution of meanders and prediction of meander migration rates. These models are expected to constitute valuable tools to assess the impact on the physical environment of both natural and man-induced meandering morphological changes.       This research program will result in the training of 3 Ph.D. Students, 3 M.Sc. students and 1 B.Sc student.