Temporal variation in downstream sediment transfer in the Lower Yellow River

An index of sediment transferring function (F-s), which is defined as the ratio of sediment output from a given river reach to the sediment input to this river reach, is applied in this study to reveal the temporal variation in the downstream sediment transfer of the Lower Yellow River. It is found that in the past 50 years, sediment transferring function index (F-s) of the Lower Yellow River showed a decreasing trend. To elucidate the formative cause, the temporal variation in F-s has been compared with the temporal variations in a number of drainage-basin and river-channel factors. The results show that the decreasing trend of F-s, is basically synchronic with the decreasing trends in the area-averaged annual precipitation in the upper and middle drainage basin and in the index of reservoir regulation (defined as the percentage of high-water season flow of the annual total) at Lanzhou and Sanmenxia stations. The F-s, index increased with the total area of all soil conservation measures, the quantity of annual water diversion and its percentage of the annual flow. Thus, the changing drainage basin factors have resulted in the decrease in the sediment transferring function of the Lower Yellow River.