Analysis of the Characteristics of Discharged Sediment in Yangtze River Estuary

Abstract

The global estuarial studies have focused on water and sediment flux into the sea and the effect of human activities on the evolution of estuarial water and sediment. In the present study, we elaborated the impact of human activities on the water-sediment relation based on the water and sediment features at Datong Station (1951-2008). The results showed that the annual runoff of several years was slightly increased in 1990s in Yangtze River (Yangtze) River estuary. The changes were not obvious in these years. The suspended sediment flux (SSF) showed a phased downward trend, which was associated with water storage of the Three Gorges reservoir, the middle-and down-stream river-lake relationship, artificial sand excavation and water drinking and regulation. The ratio average of suspended sediment less than 0.01mm and 0.05mm was increased from 1987 to 2002 than the value before 1986. The value reached the maximal in 2003, and afterwards the sediment flux ratio of these two particle sizes was decreased. After 1986, the total SSF was reduced. The SSF less than 0.01mm showed a wavy decline along with the increase of suspended sediment ratio, while the SSF less than 0.05mm was decreased along with the reduction of the total suspended sediment flux. Meanwhile, the average of median suspended sediment particle size was 0.027mm before 1986 and was 0.0094mm from 1987 to 2008. The inflexion point appearing in 1986 was consistent with the inflexion point of SSF reduction. It was directly related to water storage of the Gezhouba Dam. The median particle diameter of riverbed sand had an increase of 0.01mm/10a in average after 1977. The maximal particle diameter of riverbed sand had changed little. Both suspended sediment and bed sand became fine along the estuary and slightly became coarse in the mouth, indicating that it was functioned as the estuarial filter. The above observations would provide valuable insights for science and objective evaluation of the effect of human activities on an estuary.