Variations in runoff, sediment and channel silting in the upper Yellow River

The runoff in the Yellow River mainly comes from the Upper Area. With the social and economic development, reservoirs constructed in the trunk stream influence the stream flow greatly. Firstly, the changes of precipitation, runoff and sediment of the Upper Area in recent 20 years are analyzed in this paper. According to the runoff analysis on Hekouzhen station, runoff in the flood period is 70% of annual runoff and 30% in dry season before the reservoir construction, runoff in the flood period is 44% of annual runoff and 56% in dry season after the reservoirs construction. The average aunual sediment is 1.686*10(8) t before 1967, 1.158*10(8) t in the year 1968 to 1986, 0.401*10(8) t in the year 1987 to 1993. Then, the channel variation from Lanzhou to Hekouzhen is also studied with the sediment flux and section methods. The channel from Lanzhou to Hekouzhen silts 0.509*10(8) t sediment per year before the Liujiaxia Reservoir construction, erosion 0.28*10(8) t sediment per year in the early utilization period of reservoir and silts 0.373*10(8) t sediments per year after the year 1983.