中文摘要：

以输出某一河道的泥沙总量与进人这一河道的泥沙量之比来定义河道输沙功能，以此为指标研究了黄河下游输沙功能的时间变化。研究表明，近50年来黄河下游河道输沙功能表现出随时间而减小的明显趋势。在总的减小趋势中，由于水库运用方式与下游水沙组合的不同，河道输沙功能指标具有明显的差异，可以划分为6个阶段。1986～1997年，由于降水偏少，且人类大量引水，黄河下游进人连续枯水的水文系列，河道萎缩，输沙功能迅速降低，此时段中输沙功能指标的时段平均值为0．62，为有水沙记录以来最低的时期。对于黄河下游输沙功能指标与流域因子和河道特性因子的时间变化系列进行了比较，以揭示输沙功能减小的原因。结果表明，黄河下游河道输沙功能指标与流域平均年降水量、兰州站和三门峡站汛期径流占年径流百分比、游荡段典型断面平滩水位下断面面积、花园口站和高村站水面比降等因子有同步减小的关系，并随流域水土保持面积、人类引水量及其占天然径流量比率的增大而增大，说明这些因子的变化导致了黄河下游输沙功能的减弱。

英文摘要：

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 （Fs）, 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 （Fs） 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 Fs 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 Fs 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 Fs is basically synchronic with the decreasing trends in the areaveraged 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 Fs index increased with