Temporal variation in the sediment load of the Yangtze river and the influences of human activities

Data on sediment discharge and suspended sediment concentration (SSC) at two hydrological stations from 1951 to 2000 were utilized to study the variation in river sediment supply to the delta. Literature and documents on dam construction and water withdrawal were collected, and combined with field investigations on deforestation/afforestation and extraction of riverbed sediment, to examine the influence of human activities on river sediment load. From 1950ʹs to 1960ʹs, the river sediment discharge and SSC increased by 10 and 12%, respectively. Since 1960ʹs, both values have shown a significant reduction, with sediment discharge 34% lower and SSC 38% lower in the 1990ʹs than in the 1960ʹs. These changes are found to be governed by the balance between two aspects of human activities: deforestation and dam construction. It was predicted that river sediment discharge and SSC in the future 100 years would probably be reduced to less than 50% of the present (the average of the past 50 years) due to human activities especially the Three Gorges Dam, which will be put into operation in 2003. The effect of this reduction on the deltaic coast is also briefly addressed.