THE FLOW RESISTANCE AND RIVER-BED CONDITION IN THE SHALLOW RIFFLE ON GRAVEL-BED RIVERS

Abstract

 In the riffle of a gravel-bed river with a wide grain size, sediment transport corresponding to the magnitude of the flow rate occurs. The purpose of this study is to obtain basic knowledge for sediment transport modeling in riffle under the ordinary flow rate. The six field surveys were conducted on the Nagara River, and three cases of experiments were conducted in the experimental flumes. For the observed hydraulic values, the magnitude of flow resistance, the balance between the movement limit of surface sediment mixture and the tractive force were examined. As a result, Hey's and VPE with the relative water depth as a parameter were able to evaluate the observed values of U/U^* relatively well. In the process of continuous water flow, partial sediment movement occurred and the process of coarsening the surface layer of the riverbed was observed in the flume. However, it was suggested that the balance of the actual river riffle would be unstable due to various fluctuation factors.