Sediment rating curves in the Ningxia-Inner Mongolia reaches of the upper Yellow River and their implications

Abstract In this study, the relation between water discharge and suspended-sediment concentration (SSC) was analyzed based on daily water discharge and SSC recorded at six stations in the Ningxia-Inner Mongolia reaches of the upper Yellow River in flood seasons from 1952 to 1986. The Pettitt statistical method was used to test the abrupt changes in the time series of discharge and sediment concentration. The results indicate that the time series of discharge in Ningxia-Inner Mongolia reaches of the upper Yellow River can be divided into two periods, i.e., before 1969 and between 1969 and 1986. In these two periods, the third-order polynomial function could be used to describe the relationship between water discharge and SSC during the flood periods, indicating that sediment transport in the Ningxia-Inner Mongolia reaches was influenced by the complex processes of water and sediment inputs from the upstream and tributaries and also by the channel boundary conditions. The relation between SSC and the water discharge of low and moderate floods ( Q 3 /s) was fitted by sediment rating curves of a power function form. The sediment rating parameter b is higher in the upper section of the Ningxia-Inner Mongolia reaches due to a higher stream power there, and both the cross-section shape and river bed material determine the value of log( a ). Although a 40% decrease in sediment transport during the flood periods due to the impoundment of the Liujiaxia Reservoir and sediment-checking dams and the implementation of soil and water conservation programmes in the Ningxia-Inner Mongolia reaches of the upper Yellow River, the sediment transport regimes during 1952–1986 did not change.