The Response of the Channel Form Adjustment at the Wandering-braided Reaches of the lower Yellow River to Flood Events

Based on data from over 200 flood events covering a wide range of sediment concentration of the lower Yellow River from 1950 to 1985 and recent experimental data, this paper reveals the complex response of channel transverse adjustment at the wandering-braided reaches of the lower Yellow River to flood events with different sediment concentrations. The results show that the flood events can induce large extent of channel transverse deformation. And flood events with different sediment concentrations have different behaviors of fill-scour and ways of channel adjustment. The variations of the channel cross-section are firmly related to and exhibit complex relationships with the variations of sediment concentrations of flood events. When the sediment concentration of the flood events is low, the width to depth ratio of the channel will increase with it and when it increases to a certain degree to the range of hyper-concentrated flow, the width to depth ratio will decrease with the increase of sediment concentration. The channel metamorphosis controlled by channel fill and scour behavior is largely affected by the situations whether flood overflows floodplain or not. The over floodplain floods often carry heavy sediment load and cause the flow scouring in main channel and the sediment depositing on floodplain in large quantities, and as a result, the shallow and deep channel is formed. From the above results, the qualitative prediction relationships of river metamorphosis of Schumm's could be modified.