Secondary flow and bed form in compound sinuous channel for steady and unsteady flows

Flow structure and bed form in a straight channel with sinuous main channel are discussed based on experimental results for steady and unsteady flows. A compound sinuous channel with movable bed in main channel was used. The sinuous channel means the sinuosity (=I/lambda, 1: curved channel length, lambda : meandering wavelength) of channel is smaller than 1.3. The reason why we used a sinuous channel is that Japanese river has a small sinuosity. Bed form was measured by a ultra-sonic level meter and secondary flow in a cross section was visualized by a submergible video camera. The results indicate that the flow structure and bed form affect each other. Secondary flow scours the bed and makes sand bars, and then a new secondary flow is produced behind the crest of sand bar. In the case of unsteady flow, the rising of discharge affects the bed form slightly, but the falling of discharge impacts on the bed form notably.