STUDY ON DEFORMATION MECHANISM OF EXPANSION AND CONTRACTION SECTION IN SMALL RIVERS

Abstract

In this study, attention is paid to the formative process of expansion and contraction section of small river, the Nukui, which run through near the Hiroshima University. At the same time, the effects of bed material and vegetation in the channel on the plane form formation are also noted.

It becomes clear from the observation result of riverbed for the expansion and contraction sections, the characteristic longitudinal profile of riverbed, the particle-size distribution of mixed bed material parallel to the axis of the mainstream, and strength of roothold of vegetation that protects the riverbank of a contraction section.

In the expansion and contraction sections of the Nukui River, the first process of plane form formation is in capture of the wash load by the vegetation, which grows thick at depositing site. Moreover, it is clarified that the longitudinal profile of a riverbed is affected by the longitudinal distribution of the bottom sheer stress, which is determined by the channel plane form, and by the moving characteristics of the bed material of mixed particle size.