Temporal variation in suspended sediment concentration of the upper Changjiang River and its tributaries
长江上游干支流悬移质含沙量的变化及其原因

Based on water,sediment and precipitation data from the upper Changjiang River and its tributaries,a study has been made of the temporal variation in suspended sediment concentration in relation with the variation in precipitation and human activities.The variations in suspended sediment concentrations in the main stream and tributaries are not synchronic,and some complicated variation can be seen.The variation in precipitation can only explain 15.86%~37.21% of the variation in suspended sediment concentration,and thus variation in precipitation is not the main cause for the variation in suspended concentration.Using the analysis of double-mass curve,the effect of human activities on the variation in suspended concentration has been studied.The suspended concentration of the lower Jinsha River increased ofter 1983.This can be explained by the large-scale mining and road and urban construction,which not only disposes huge quantities of soil and rock debris to the river,but also results in the reactivation and releasing of the previously deposited mass-wasting and debris flow materials.The double-mass curve for the Minjiang River shows three breaks,which may be explained by reservoir construction and deforestation and reforestation.The suspended sediment concentration of the Jialing River decreased after 1984 because marked sediment reduction effect has been achieved by soil and water conservation measures.The suspended sediment of the Wujiang River increased after 1967 and then decreased after 1983,the former can be related to the vegetation destruction that enhanced soil erosion and the latter to the construction of reservoirs that trapped sediment.Compared to the 4 tributaries,the suspended sediment of the main stream of the upper Changjiang River shows smaller variation in suspended sediment concentration.As the suspended sediment concentration of the lower Jinsha River increased after 1983 while that of the Jialing River decreased after 1984,they offset each other and thus the variation in the suspended sediment concentration of the Yichang station is much smaller.The results of a multiple regression analysis shows that the contribution percentages of the variation in suspended sediment of Pingshan,Gaochang,Beibei and Wulong stations are 28.5%,12.6%,44.2% and 14.7%,respectively.