龙羊峡、刘家峡水库蓄水运用对下游洪水的影响

Effects on Flood in the Lower Reaches After Storing Water and Operation in Longyangxia and Liujiaxia Reservoirs

根据36年汛期(6～10月)实测洪水系列,按龙羊峡、刘家峡两席设计中规定的运用原则,进行调节计算,分析两水库联合运用后,对下游兰州等断面设计洪水的影响,初步认为:1)汛期多年平均水量减少21.9%;2)各年时段洪水特征值年际问变化规律不受影响;3)洪量频率分布型式由偏态铃形分布趋向于乙字形分布。用同频率地区组成法预估吴堡、花园口等断面的设计洪水,由于受龙羊峡、刘家峡水库影响减少水量范围为:相应千年一遇设计洪水最大5天水量减少4～5.7亿m^3,12天水量减少10～12亿m^3。

The effects on flood design of Lanzhou and the lower sections after joint operation of the two reservoirs have been analysed based on 36-year observed data during flood season (from June to October) in the light of the operational principle provided by the design of Longyangxia and Liujiaxia reservoirs. It is considered preliminarily that:(1)The average wvater volume for many years during flood season reduces 21.9%; (2)The law of Change of eigenvalues of time-interval flood in each year is not affected;(3) The curve of flood frequency distribution is tending from skew-bell shapo distribution to Z shape distribution. It is to pre-estimate the design flood of Wubao and Huayuankou sections by using a composed method of areas with same frequency. Owing to effects of Longyangxia and Liujiaxia Reservoir, the maximun amount of water in 5 days and 12 days of design flood occorred once in a thousand years are reduced 400—570 million m^3, and 1—1.2 billion m^3 repectively.