Study on Bankfull Flow Discharge of Ningmeng Reach in Upper Yellow River

By analyzing the filed data of flow and sediment process in Ningmeng Reach during 1965—2004,the bankfull discharge in this river was investigated and the result showed that the bankfull discharge decreased with time during this period since the river cross-section shrank,the bankfull discharge of the whole reach was 3 600~5 800m3/s in the middle 1960's while it decreased to 1 100~3 600m3/s in 2004,and bankfull discharge decrease of Neimenggu reach are more than that of the Ningxia reach.Especially,after building of the Longyangxia Dam in1986,bankfull discharge at Sanhehukou hydrologic station has been decreased from 4 100m3/s in 1986 to 1 100m3/s in 2004.Relationship between bankfull discharge and runoff of flood season was analyzed and the result showed that the former augmented with the increasing of the latter.Besides it is found that this relationship was not only influenced by runoff but also by flood process.When annual runoff is 20 billion m3 or runoff in flood season is8 billion m3,bankfull discharge of Ningxia reach and Neimenggu reach was about 3 100m3/s and 2 850m3/s,while they were 4 300m3/s and 4 000m3/s when annual runoff was 30 billion m3 or runoff in flood season was 17 billion m3.The results of this paper will be profit for river regulation in Ningmeng reach.