Grain-size characteristics of suspended sediment in the Yellow River, China

Based on the data from the Yellow River and its tributaries, a systematic study has been made of the spatial and temporal variations in grain-size feature of suspended sediment. The grain-size characteristics of suspended sediment in the Yellow River basin are closely influenced by precipitation, seasonal alternations of wind and water action, and the nature of surface materials. The lower the mean annual precipitation, the stronger the wind action, the coarser the surface loess materials, the coarser is the suspended sediment. In particular, grain-size characteristics of suspended sediment of the middle Yellow River's tributaries are controlled by hyperconcentrated flows with suspended sediment concentrations of 300,000-400,000 mg/l or more. At a station, the relationship between grain-size and suspended sediment exhibits two peaks with percentages of the >0.05 mm suspended sediment occurring at both low and very high suspended sediment concentrations. Based on the data from all the tributaries of the middle Yellow River, an optimal grain-size composition of suspended sediment has been identified that leads the annual suspended sediment concentration to the highest values. The long-term variation of grain-size suspended sediment in the Yellow River can be related to variations in precipitation and human activities. The 30-year record from Longmen station shows that during the 1960s, the suspended sediment size increased, but since the 1970s, it has declined. Controlled by the influencing factors, grain-size of suspended sediment in the middle Yellow River decreases from northwest to southeast. (C) 1999 Elsevier Science B.V. All rights reserved.