中文摘要：

无定河流域1971～1989年的年均流量、悬移质含沙量及输沙率比1954～1970年的明显变小，而月均水沙过程曲线也发生了明显变化。上述水沙过程的变化受到1970年以来人类活动的强烈影响，而淤地坝建设是主因。为探讨淤地坝的减沙效应，提出淤地坝有效减沙面积这一概念，并拟合了动态变化的淤地坝有效减沙面积与年份之间的关系，发现该关系曲线与无定河流域各年代产沙量的变化情况相符。自1990年以来无定河流域淤地坝有效减沙面积呈明显递减趋势，导致了自上世纪90年代以来该流域的产沙量出现增大现象。为了抑制该流域的产沙量，势必需要加大淤地坝建设的力度。如果想使该流域的产沙量逐渐减少，则至少要使流域内年淤地坝有效减沙面积逐年增加。

英文摘要：

The mean annual discharge, sediment concentration and sediment delivery ratio in the period from 1970 to 1989 are evidently smaller than that in the period from 1954 to 1970. The relations between monthly mean discharge and sediment concentration are different comparing the two periods of time. These phenomena have been influenced by human activities in which the dam building has been the dominant factor since 1970. To discuss the dam effect on decrease of sediment yield a concept of efficient area of dams was advanced. The relation between the annual efficient area of dams and years was fitted. The results show that the varying trend of the relation curve is coincident with the variation of the sediment yield in the decade＇s distribution. Since 1990 the increase of the sediment yield has resulted in evident decrease of the efficient area of the dams in the Wudinghe River basin. It is necessary to build dam largely and rapidly for restraining the increase of sediment yield in the river basin. If we want the annual sediment yield in the river basin gradually decrease, the annual efficient area of dams must be gradually increased year by year.