RESERCH ON BED SURFACE MATERIALS AROUND A FLOW ATTACK POINT AND BED SCOURING

Abstract

The bed of gravel bed rivers is composed of the bed materials with wide grain size distribution. In general, when the flood flows in the gravel bed river, the bed material which responds to the tractive force of the flow covers the surface of riverbed. The Asa river which is the main tributary of the Tama river is not necessarily sound in view of the sediment transportation, because the large amount of gravel excavation had been done in the past and the sediment supply from the upstream is not abundant. In this research, we clarify the relation between the bed variation and grain size distribution at the point of flow attack around 9.2km in the Asa river. Appearance of “Dotan” on the riverbed surface dwing floods shows to influence the management and maintenance of the river.