1984年春节礼河发电厂水槽子水库空库冲刷效果分析

1984年春节，以礼河发电厂大体上按照上述方法实施水槽子水库的空库冲刷，其流量、冲刷含沙量过程如图15所示。这次冲沙总耗水505.4万m3，冲刷量为26.5万m3（断面法），冲刷每1m3淤积物的耗水量为19.1m3。

图15表明，流量呈“马鞍形”变化，冲刷含沙量亦相应呈“马鞍形”起伏。第二次大流量冲刷的平均含沙量高于头一次大流量末尾的含沙量，冲刷效率因而得到提高。但是，这阶段冲刷含沙量提高的数值比预料的低，衰减也较快。这种情况估计与本次冲刷安排第二阶段（小流量空库）时间过长有关。冲沙前，因对以下的一些特殊因素估计不足，结合其他工程检修需要，安排了4d的小流量空库时间。地处高寒山区的水槽子水库，2月初晚间气温很低，新暴露的淤泥面被冻结，强烈的干风数天内又使黏性淤泥表面形成2cm以上的风干层。第二次大流量冲刷时，主槽两侧淤泥的活动性远较头一两天差，水槽子水库这次试验表明，第二阶段即小流量空库的时间不宜过长，似应控制在淤泥表面不被冻结和不形成厚的风干层为宜。

曹叔尤同志参加了本文的部分工作。

式中，为点估计值；C为置信度；C′=（1+C）/2为显著水平；（i）为自由度i的χ2分布的r上侧分位点；θL为区间估计的下限值；θU为区间估计的上限值。

2.任务可靠性评估

（1）点估计。

任务可靠性点估计值计算公式如下：

图15　水槽子水库1984年空库冲沙综合过程

参考文献

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6　彭润泽，常德礼，白荣隆，谭伟民等.推移质三角洲溯源冲刷计算公式.泥沙研究，1981（1）(www.xing528.com)

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Rational operation of Drawdown flushing in Shuicaozi reservoir on Yili River

Du Guohan Zhang Zhenqiu

（Institute of Water Conservancy and Hydroelectric Power Research）

Abstract：The Yili River Hydropower Station，which has four hydropower projects in cascades，is developed between two neighbouring river basins.The Shuicaozi Project，which is the second stage of the cascades，functions as a seasonal storage reservoir and diversion work conveying the discharge from the Yili River to the Xiaojiang River for power production.Since no bottom outlet for sediment flushing was installed，so from the time of impounding of the reservoir in June 1958 up to January 1981，sediment deposited in the Shuicaozi reservoir totalled 8，160，000 m3 i.e.85 percent of its total storage capacity had been lost.For the sake of sedimentation reduction and recovery of storage capacity，the measure of drawdown flushing has been used in the Shuicaozi reservoir.

Based on the analysis of field data and theoretical calculation，the characteristics and rational operation of drawdown flushing in the Shuicaozi Reservoir are investigated.

The characteristics of drawdown flushing in the Shuicaozi reservoir can be summarized as follows：（1）The region affected by flushing，the pool water level for starting retrogressive erosion and the longitudinal profile performed by drawdown flushing are rather fixed.（2）As a coefficient of reservoir emptyingα is used for representing the extent of utilization of the flow energy in the drawdown flushing，it is evident that the flow erosion capacity was not fully developed in the past flushing events.（3）In the first stage of drawdown flushing，the sediment sluiced comes mainly from the deepening of the main channel on the reservoir bed，and afterwards，sediment sluiced out from the reservoir comes mainly from the banks of the main channel in the manner of slope sliding and bank collapsing.（4）On the top-set of the delta，deposition in the main channel can be sluiced out in drawdown flushing，but upon the flood plain the deposition is accumulated gradually.On the front-set of the delta and in the deposition reach in front of dam where the river valley is narrow，as the main channel is deepened in flushing，the unconsolidated silt slides towards the main channel slowly，the elevation of the deposited reservoir bed can be lowered down in the whole cross-section.

The occurrence of channel bank sliding and unconsolidated mud flow is closely related to the pore water pressure in the deposit.The calculated theoretical results show that the quantity of seepage water from the deposit is very small in a period of several days，and the pore water pressure keeps approximately its original value in the drawdown flushing process.

The calculated theoretical results obtained from the aplication of a parabolic partial differential equation show that if the discharge，duration and water volume used in flushing event are kept constant，the larger the drop of water level in front of the dam，the larger the quantity of eroded sediment will be，and the faster the drawdown rate of pool water level，the greater the quantity and intensity of erosion will be.

The operation of drawdown flushing in the Shuicaozi reservoir is suggested as follows：（1）In drawdown flushing，the pool water level in front of the dam should be fully drawn down.（2）A saddle shaped discharge hydrograph for drawdown flushing should be used.That is，in the first stage，a large flow discharge is used for drawdown flushing，it aims to deepen the main channel.Then，as soon as the main channel is formed the flushing discharge should be cut down.Finally，the large discharge erosion process is repeated，it aims to sluice out the accumulated sediment from slope sliding and bank collapsing and to enlarge the cross-section of the main channel.

The suggestion stated above was adopted by the Yili River Hydropower Plant in the drawdown flushing in February 1984，the practice indicated that the silt concentration in the flushing flow was increased and the water consumption of drawdown flushing was reduced obviously.