Effect of sediment sink of lower Yellow River on grain size of sediment flux to the sea

The lower Yellow River can be regarded as one of the sediment sinks in the river drainage basin,which plays an important role in the sediment budget of the river system.Through sediment deposition and scour in main channel,composition of sediment in motion changes;through sediment deposition on floodplain and bank erosion,exchange occurs between the sediment on floodplain and the sediment in motion.Thus,composition of suspended sediment changes along the river.It is found that sediment deposition has different effect on various fractions in sediment flux to the sea.The percentage of fractions finer than 0.01mm in the sediment flux to the sea is positively correlated with sedimentation amount in the lower Yellow River,but negative correlations exist between sedimentation amount and the percentages of fractions in the range from 0.025mm to 0.05 mm and coarser than 0.05mm in the sediment flux to the sea.The average diameter of sediment flux to the sea is found to be negatively correlated with the annual shift of the thalweg of the lower Yellow River.Since the mid-1960s,especially since the 1980s,water discharges of the lower Yellow River decreased significantly and the channel shrinkage occurred,the channel width decreased and so did the annual shift of the river's thalweg.As a result,bank erosion weakened,and the sediment exchange between main channel and floodplain became less intensive than that in the previous period.Since the floods in the main channel could get less fine sediment from the floodplain,the grain size of suspended sediment flux to the sea tended to become coarser.