关键词: 输沙功能, 流域因子, 人类活动, 时间变化, 黄河

Abstract:

The decline in sediment transferring function of the lower Yellow River has drawn attention from the scientific community,the government and the public.Hence,finding out the cause for it is an important and urgent issue in harnessing the Yellow River,both in theory and in engineering practice.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 sediment transferring function 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.Due to the changing operation mode of the Sanmenxia Reservoir and the varying combinations of runoff and sediment load,the temporal variation of F_s can be divided into 6 stages.During the period from 1986 to 1997,due to the decrease in annual precipitation and increase in water diversion,the incoming flow of the lower Yellow River was significantly less than the average.As a result,channel shrinking occurred,and the index of sediment transferring function decreased to 0.62,the minimum in the hydro-metrical history.To elucidate the formative cause for the decrease in sediment for the sediment transferring function,the temporal variation in F_s has been compared with the temporal variations in a number of drainage basin factors,including drainage basin factors and river channel characteristics.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,the index of reservoir regulation（defined as the percentage of high-water season flow of the annual total） at Lanzhou and Sanmenxia stations,the bankfull cross sectional area of the typical braided reach and the water surface gradient of the Huanyuankou-Gaocun reach at a given discharge.The F_s index increased with the total area of all soil-water conservation measures,the quantity of water diversion and its proportion of the annual flow.Thus,it is demonstrated that the changing drainage basin factors and channel characteristics resulted in the decrease in the sediment transferring function of the lower Yellow River.

Key words: sediment transferring function, drainage basin factors, human activities, temporal variation, Yellow River