The suspended sediment dynamics in the Inner-Mongolia reaches of the upper Yellow River

Suspended sediment dynamics are still imperfectly understood, especially in the upper Yellow River where few studies on this issue have been conducted. This study analyzed the variability in suspended sediment concentration at different temporal scales (within-flood, monthly-seasonal and annual). Using a dataset up to 49 years long (1954–2002) at Toudaoguai station, this paper provided insight into the characteristics of suspended sediment transport in the Ningxia-Inner Mongolia reaches of the upper Yellow River. The results show that, in a single flood event, changes in SSC are not simultaneous with changes in discharge, resulting in counterclockwise hysteretic loops, clockwise loops or figure-eight loops. The C–Q loops and sediment rating curves for different seasons had different characters. The diversiform C–Q loops in the Inner Mongolia reaches of the upper Yellow River may be mainly caused by the sediment inputs from tributaries, the different propagation velocity of sediment and water discharge, spatial and temporal storage–depletion processes of available sediment. At annual scale, the variations of annual mean discharge and SSC displayed a similar gradually deceasing trend, and the relation between water discharge and SSC during 1954–2002 could be described by a cubic polynomial function. Since the joint operation of Liujiaxia and Longyangxia reservoirs after 1986, the transport capacity of the Upper Yellow River has been much reduced.