On sand bed rivers the author made simultaneous observations of the river-bed formation along witb tbe vertical distribution of turbidity at the time of flood flow, using the echosounder and turbidity meter, As a result of his observations it has become clear that there is a strong current curling up from the river-bed when the water-level is rising and the river-bed flattens out, whereas, when the water-levei is lowering and sand-waves with considerable height are developing, the same current does not appear but becomes rather a quiet flow.