Sediment transport efficiency of floods in the lower Yellow River in relation with water-sediment combination and channel geometry

Based on data from 274 flood events in the lower Yellow River,a study has been made for the sediment transport efficiency of floods in relation with water-sediment combination and channel geometry.Three thresholds have been identified in the variation of channel sediment delivery ratio(SDR) with event-average water discharge.It has been found that when event average suspended sediment concentration C_(mean) was higher than 34.02kg/m~3,or the index C_(mean)/Q_(mean) was smaller than 0.01kg·s/m~6,no deposition occurred.The SDR for the braided reach was the smallest,that for transitional reach the second,and that for the confined meandering reach the largest.In this order,the threshold C_(mean) for no-fill and no-scour state increased.It indicated that a narrower and deeper channel can better remain no-fill and noscour state at higher C_(mean) values than a wider and shallower channel can.