BED VARIATION IN A BRAIDED CHANNEL DURING LARGE FLOOD

Abstract

The Hii river is known as a typical river with braided channel bed. Large sand waves are formed on the braided bed. It is considered that the flow resistance changes as bed elevation of the main channel changes during a flood. Therefore, evaluating the temporal and spatial variation in the flow resistance is important to understand the flood flows and bed variations in the Hii river. In this study, first, temporal variations in the resistance during the 2011 May and 2006 July floods of the Hii river are evaluated by the Manning’s roughness coefficient in quasi-steady flow analysis. Next, the unsteady flow analysis is conducted using the temporal variation in the roughness coefficient determined by the quasi-steady flow analysis to investigate the mechanism of bed variation in the Hii river. From these investigations, we conclude that the analysis method presented in this study is useful for the flood flow analysis in the Hii river.