Impacts of the Gezhouba and Three Gorges reservoirs on the sediment regime in the Yangtze River, China

The sediment regime of the Yangtze River (Changjiang) has been altered by intensified human activities over the past decades, particularly dam construction. To investigate the impacts of dam building on the sediment regime in the Yangtze River, two of the largest reservoirs on the upper reach, i.e. the Gezhouba reservoir and the Three Gorges reservoir, have been selected as case study sites. To analyze the changes in sediment regime between pre-dam and post-dam periods, the whole study period was divided into three sub-periods according to the years when these two reservoirs started to store water. On the basis of the time series of daily water discharge and sediment concentration from four key hydrological stations, i.e. Cuntan, Yichang, Hankou and Datong, the alterations of annual, seasonal, monthly and daily sediment regimes in different sub-periods were investigated and the driving forces were explored. The results revealed: the impacts varied with reservoir storage capacity, operation modes and the distance between the target reservoir and the case study site; Sediment trapping in reservoirs together with soil and water conservation measures was of significant impacts on different time scales of sediment regimes. The results of the study could provide references for the assessment of impacts of dam construction on the health and stability of the Yangtze River ecosystem.