Features and trends of recent changes in runoff and sediment regimes in wide-valleyed desert reach of Upper Yellow River

This paper is intended to reveal important characteristics and varying tendency of the runoff and sediment load measured at the major hydrometric stations on the Upper Yellow River by using statistical analysis,correlation analysis,moving average and the Mann-Kendall trend test.The research results show,among others,that the feature of runoff and sediment load from different source areas has become more apparent since 1990 compared with those before 1990.The average annual runoff and sediment load measured at Xiaheyan,Shizuishan and Toudaoguai hydrometric stations in 2000-2009 decreased by 24.8%~39.8% and 36.6%~73.6%,respectively,with less contributed in the flood seasons.Meantime,the relation of water flow and sediment load changed insignificantly.Besides,the trend analysis shows significant decrease in both runoff and sediment load,with more significant decrease in sediment load,especially at Toudaoguai hydrometric station.Meanwhile,a preliminary analysis of factors affecting the runoff and sediment variation,such as precipitation,water and sediment diversion,incoming water and sediment load from tributaries,reservoir operation and river channel adjustment is made.