EFFECTS OF SILT ON ALTERNATE SANDBAR MORPHOLOGY COMPOSED OF SANDY MATERIALS

Abstract

 In September 2018, a large number of slope failures occurred in the Atsuma River basin due to the Hokkaido Iburi Eastern Earthquake. The main channel morphology is alternate sandbars in the middle and lower reaches of the Atsuma River having a gentle gradient. In this study, we conducted flume experiments to know the effects of silt on alternate sandbar morphology composed of sandy materials in the Atsuma River. Results showed that the wavelength and wave height of sandbars were affected when the rate of silt increased by more than 10% compared to the volume of equilibrium bed load. Sandbars almost disappeared when the rate of silt exceeded 30%. In addition, silt deposited locally where the boundary areas between sandbars and low flow channel. This is because silt is transported as suspended load on sandbars so that it hardly deposit there. While, at the boundary area, silt is captured by the water, flows from the front edge of sandbars to low water channel, as well as bed load material.