Decadal trends and causes of sedimentation in the Inner Mongolia reach of the upper Yellow River, China

Using hydrological and sediment data, this study investigated decadal trends in sediment erosion/deposition in the Inner Mongolia reach of the upper Yellow River. The calculated yearly sediment erosion/deposition show that the reach was dominated by aggradation, degradation, and aggradation successively in three periods with the years around 1961 and 1987 as break-points. By constructing relations between water discharge and sediment load, the contributions of key factors to the changes in sediment erosion/deposition in the reach were quantified. Results show that the sediment retention behind the main stem dams, the increase of natural runoff, and the decrease of sediment inputs from tributaries and upstream watershed were the main factors causing the transition from aggradation during 1955-1961 to degradation during 1962-1987. The reduction of natural runoff, the decrease of sediment retention behind dams, and the rise of sediment supply from tributaries were the key causes of the reversal from degradation in 1962-1987 to aggradation in 1988-2003. Water diversion has played an important role in the long-term aggradation of the Inner Mongolia reach. The main stem dams had functioned to alleviate siltation after 1961, but their effects on siltation reduction had been gradually diminishing since the 1990s. Copyright (C) 2015 John Wiley & Sons, Ltd.