Study on sediment transport in the lower Yellow River during flood period

Based on the data from 144 flood events during the periods 1950-1960 and 1969-1985,this paper deals with sediment transport in the lower Yellow River.The results show that the channel sediment delivery ratio (SDR) decreases with the increases in the event-averaged sediment concentration and the "incoming sediment coefficient" expressed as sediment concentration divided by water discharge.There is an optimal flood discharge of 4000 m³/s,at which the SDR reaches its maximum.The event SDR is negatively correlated with the event maximum sediment concentration C_max;when C_max is larger than 300 kg/m³,the SDR is smaller than 0.50,indicating that the SDR of hyperconcentrated flows is rather low.The SDRs of floods coming from different source areas are different.The floods whose runoff mainly came from the clear water area above Hekouzhen had a SDR larger than 0.60;those from the "fine sediment producing area" had a SDR larger than 0.50;those from the "coarse sediment producing area" had a SDR smaller than 0.50.The SDR of a given flood event is found to be related with the combination of sediment and runoff from different source areas;when the sediment from the coarse sediment producing area made up of 50% of the total,or the sediment from the fine sediment producing area made up of 40% of the total,the SDR of the flood events reached its maximum.