A Study On The Dynamic Process Of Meandering Rivers

As the basic element of sinuous rivers, the regular and similar river meander planforms imply profound dynamics. River meanders on alluvial sinuous river migrate crossstream and downstream continuously, which is called the dynamic process of river meanders. Research on the dynamic process of river meanders plays an important role on river development and regulation, locating of river crossing bridges and highways along rivers, oil and gas exploration and ecological restoration of rivers etc.Research on river meandering involves different spatial and temporal scales, as well as multiple subjects. In this thesis, river meanders on alluvial sinuous river are interdisciplinarily studied from the aspect of hydrodynamics, river dynamics and morphodynamics. Main contents and innovations are:The planforms of large scale rivers were studied by multi-scale analysis and fractal analysis. A set of methods for meander recognization, generalization and statistic analysis was also developed. Analysis shows that fractal dimension can describe the meandering and irregularity of the planforms of large scale rivers better than curvature. Small scale fractal dimensions reflect the development of river meanders, while large scale ones reflect the irregularity of landform of watershed.A three-dimensional mathematical model was established to simulate the flow in open channel. Numerical experiments were carried out with this model to study the influence of curvature, water depth, channel width and bed topography on flow in channel bends. Scale analysis was also carried out for characteristic flow parameters as a foundation of simplification of control equations to two-dimensional and one-dimensional ones. Numerical simulation results show that the typical features of primary flow, secondary flow and velocity redistribution in natural river bends are closely related to the special planform and flow depth conditions of natural river meanders. The lateral redistribution of flow is significant when water depth is small. The main stream approaches the concave bank upstream the bend vertex when river width is small.The unsteady flow of natural rivers causes strong perturbation on meander developing process. A two-dimensional model was established for sinuous channels to simulate unsteady flow movement as a pilot study on this perturbation effect. Mathematical model coupling river meander migration and landform development was established based on linear river meandering theory and conceptual deposition model. The traditional linear theory of bank erosion was improved to a nonlinear one. Simulation results reveal that rivers have the function of channel filtering to smooth out the given initial random disturbance under certain conditions.Laboratory experiments were carried out to study the characteristics of flow and sediment transport in channel bends, as well as river meander migration laws. According to the requirement of measurement in experiment, particle tracking velocimetry and high efficiency sectional topographic surveying system were developed, which was another innovational work of this thesis.