Influence of variations in suspended sediment concentration and grain size on sediment deposition of Yichang-Hankou reach of Yangtze River

Based the data measured before the construction of the Three Gorge Dam and using the empirical statistical approaches,this paper studies influence of variations in suspended sediment concentration and grain size on the sediment deposition of Yichang-Hankou reach of Yangtze River.And a regression equation between the annual sediment deposition in the Yichang-Hankou reach and the annual average suspended sediment concentration(Cmean,Yichang)at Yichang station is established in 1980-1997.According to this equation,a threshold of Cmean,Yichang is estimated as 0.734 kg/m³,at which this river reach is in a non-scour and fill state. A multiple regression equation is also established,which relates the annual sediment deposition in the Yichang-Hankou reach and the influencing variables including the annual suspended sediment concentration, median grain size of suspended load and annual flood at Yichang station,and the ratio of the flow diverted through the “three outfalls” to the total. The equation based on the data in 1980-1997 indicates that the sediment deposition in Yichang-Han-kou reach increased with the increases in sediment load,median grain size of suspended sediment and annual flood at Yichang station,and with the decrease in the ratio of the flow diverted through the “three outfalls” to the total.