Characteristics of Sediment Motion for Respective Grain Sizes of Sand Mixtures

Abstract

In sediment transport of sand mixture, the characteristic quantities of sand motion are different for each grain size, and it follows that temporal and spatial changes of bed constitution must be caused thereby. Therefore, the characteristic quantities of sand motion for each grain size should be clarified in relation to bed constitution to describe sediment transport process and subsequent phenomena in alluvial beds composed of sand mixtures. At first, mechanical properties of rough bed composed of sand mixture are investigated in relation to grain size distribution, and particularly the statistical properties of relative height and angle of escape of exposed particles are inspected by a simulation method. Next, the so-called critical tractive force for each grain size, which is one of the most fundamental quantities, is here theoretically investigated. On its estimation, the equivalent sand roughness of mixed sand bed is necessary and a new model using the concept of equivalent size of non-uniform particulate materials is proposed. Moreover, the other characteristic quantities of sediment motion for each grain size are inspected based on a film analyzing method. These research projects must give important information to describe various kinds of alluvial phenomena observed in natural rivers of which beds are composed of widely distributed sands and gravels.