River Plan-Form Movement in an Alluvial Plain

摘要

In order to study the river plan-form movement, the first step in this study isthat of developing a mathematical model. First of all, straight rivers are seldom, and indeed rivers flow nearly always have sinuous plan-forms, so that the 'natural' co-ordinate systems of their models are curvilinear co-ordinate systems. Since the river evolution and its movement cannot be studied with a purely one-dimensional approach, the model must be at least two dimensional. Moreover the complex system of secondary flow which is provided by the flow circulation across the river, in a direction perpendicular to the longitudinal direction of flow, is so important in the channel bends that the vertical profile of this velocity has to be studied and introduced in such a way that its effect is included in the model. By this means the model becomes in effect even more than two dimensional. The model is developed, tested and verified with flume experiments and also with two well-documented natural river situations, these being the river Waal in the Netherlands and the river Ishikari in Hokkaido, Japan.