Temporal and spatial variations of sediment rating curves in the Changjiang (Yangtze River) basin and their implications

Abstract

The natural hydrologic regime of the Changjiang (Yangtze River) in China has been disturbed considerably by intensified human activities over the past five decades. In this study, sediment rating curves were analyzed based on monthly data of water discharge and suspended-sediment concentration at stations in the upper (Yichang station), middle (Hankou station) and lower (Datong station) reaches of the Changjiang in different periods from 1955 to 2007. Temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics. Results indicate that human disturbances have had a substantial impact on sediment rating parameters, with the magnitude of the impact related to the scale of the river sections. As indicated by the sediment rating parameters, the sediment transport regimes between the upper and the mid-lower reaches differ significantly. In particular, the impoundment of the Three Gorges Dam in 2003 changed the sediment transport regimes in the upper and mid-lower reaches of Changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge. Furthermore, the sediment rating curve at the Datong station in 1955–1968 was applied to estimate the potential sediment load (1969–2007) in the absence of human influences. The mean annual sediment deficit caused by human activities has increased from 80 Mt/yr (1969–1985) to 250 Mt/yr (2003–2007). This indicates that intensified human activities in the Changjiang basin, especially the construction of the Three Gorges Dam, have altered the natural sediment transport process, and have thus become a dominant force in Changjiang sediment delivery to the sea.