EFFECTIVENESS OF LOCAL RIVER WIDENING METHOD IN THE SMALL AND MEDIUM-SIZED RIVERS OF ALLUVIAL FANS

Abstract

This paper aims at examination of the effectiveness in Japan of the “Local River Widening” method mainly tried in Europe. About the example site of the small and medium-sized rivers which flows through the Kiso-river fan, the follow-up survey was conducted to consider the geographical feature change process. A point-bar was formed through two flood term after construction in the site. In order to generalize the knowledge acquired from the case study, the virtual river channels of alluvial fans were set up, numerical analysis were performed on varying plane conditions. The pattern of geographical feature change was arranged by four types, and the formation factors of each type were considered by the results of analysis. The considerations with the development domain of bed forms were performed. It was suggested that the fall of average shear stress of the widening section caused formation of bar-like geographical feature.