In the upper Yellow River basin above Tangnaihai,the precipitation in winter and spring is mainly accumulated in the form of snow cover. Snowmelt is one of the main supplies of spring streamflow. The basin is one of the main runoff-forming areas of the Yellow River. The yearly runoff volumes from the basin make up over 80-90% of the inflow to the Longyangxia Reservoir and 75% of that to the Liujiaxia Reservoir respectively. It is in spring that the irrigation season is , the need for irrigating water is oft...