Effects of size heterogeneity of bed materials on mechanism to determine bar mode

摘要

In fluvial fan rivers, various types of sandbars are formed, and depending on their patterns, we have to consider management of the river system from the viewpoint of flood protection as well as conservation of river ecosystem. In spite of many researches into sand bars, it has not been well understood how the characteristics of sand bars are sensitive to various boundary conditions. This paper focuses on the bar mode as the characteristic of a sandbar, while the size heterogeneity of bed materials is focused on as a surrounding condition. We employed three approaches to clarify the effect of size heterogeneity on the mechanism determining the bar mode: flume experiment, numerical simulation and linear instability analysis. These approaches show the effects of bed material components on bar mode, with the higher number of bar mode appearing in the condition where the bed is composed of materials with wider size of distribution.