Variation Characteristics of Water and Sediment in the Middle Reaches of the Yellow River

The Yellow River is characterized by less water and more sediment,and imbalance between water and sediment. The difficult problem of governance is to deal with relations between runoff and sediment discharge. For the past 60 years,relations between runoff and sediment have deteriorated sharply. Therefore,revealing the characteristics and influence factors of the variation between water and sediment are the primary task of water and sediment research. In the paper,the moving average method and Mann-Kendall test method were used to analyze the varying tendency of water and sediment in the Middle Reaches of the Yellow River from 1950 to 2010 based on the observed data from four main hydrologic stations,namely Longmen,Huayuankou,Huaxian,and Baijiachuan. The results indicate that both runoff and sediment discharge decreases significantly in the middle reaches of the Yellow River,especially after1970 s. The results also show that the variation of runoff and sediment discharge is mainly caused by climate change,rainfall,water conservancy projects,soil and water conservation measures and so on,and human activities are turning into the most fundamental factors affecting the variation of water and sediment now.