混合砂礫の流砂量と河床変動に関する研究

Abstract

This paper describes the results of investigations concerning the bed load transportation for nonuniformsediment, armouring phenomena and the degradation of a river bed composed of graded material in the caseof no sediment supply at the upstream end.The effect of nonuniformity of the material on the bed load transportation can be expressed by thedifference of the threshold condition of movement of sediment for various size classes. The process ofriver bed degradation can be treated by using a respresentative diameter for the sediment mixture when thematerial of various grain size classes is in the moving state, on the other hand when some parts of the bedmaterial are under the threshold condition of movement river bed degradation scarcely occurs by the effectof an armour coat.Therefore authors classify the process of river bed gedradation into three regions, and propose a methodto predict the grain size frequency distribution of the armour coat on each region and to compute theamount of river bed degradation.