A study of sediment delivery by floods in the lower Yellow River, China

The concept of sediment delivery ratio (SDR) is used at the scale of channel reach to define the efficiency of sediment transport in a given river reach. Based on the data from 144 flood events during the periods 1950-1960 and 1969-1985, sediment delivery by floods in the lower Yellow River has been studied. The results show that SDR decreases with the increases in the event-averaged sediment concentration and the incoming sediment coefficient expressed as sediment concentration divided by water discharge. At a flood discharge of 4000 m(3) s(-1), the SDR reaches its maximum. The SDR of flood events strongly influenced by hyperconcentrated flows is low. Channel shape has some influence on sediment delivery ratio. A relatively deep and narrow channel may enhance the sediment carrying capacity of the river and leads to a higher SDR. Significant difference exists in the event SDR between the floods that come from different source areas. The SDR of a given flood event is found to be related with the combination of sediment from different source areas; when the sediment from the coarse sediment producing area accounts for 50% of the event total, or the sediment from the fine sediment producing area accounts for 40% of the event total, the event SDR reached its maximum.