Analysis of dam effect on sediment yield in the Wudinghe River Basin
无定河流域产沙量变化的淤地坝效应分析

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.