三门峡水库冲淤与“318运用”的影响

Erosion and deposition in Sanmenxia Reservoir and the impacts of“318 Operation”

三门峡水库自1974年开始采用“蓄清排浑”运用,2003年又在此基础上采用了非汛期运用水位不超过318 m、汛期入库流量大于1500 m^3/s时敞泄排沙的“318运用”方案。为了量化入库水沙条件和水库运用方式对水库冲淤及潼关高程变化的影响,采用1974—2018年实测水沙与库区断面形态数据,在分析水库冲淤及潼关高程变化特征的基础上,提出库区冲淤及潼关高程的平衡概化模式,建立考虑入库水沙和库水位变化的库区累计淤积量及潼关高程的滞后响应计算方法,并定量分析不同水沙条件和“318运用”对库区冲淤和潼关高程变化的影响。结果显示:2003年后来水量增加对潼关高程降低起主导作用;来水量增加、来沙量减少及汛期敞泄临界流量降低均在一定程度上使得库区淤积量减少;“318运用”一方面降低了汛期临界敞泄流量,可使潼关高程平均下降约0.08 m,库区累计淤积量减淤约0.24亿m^3,但另一方面抬升了非汛期平均库水位,可使潼关高程平均抬升约0.03 m,库区累计淤积量增加约0.24亿m^3,在一定程度上抵消了汛期敞泄临界流量降低产生的降低潼关高程和库区减淤的作用。

The Sanmenxia Reservoir has been operated by“storing clear water and discharging the turbid”since 1974.Recently,a reservoir operation scheme called“318 Operation”has been implemented since 2003.Under the control of this scheme,the water level during non-flood season should not exceed 318 m and,when inflow discharge exceeds 1500 m^3/s during flood season,the sluice gates should all open to discharge as much sediment out of the reservoir as possible.In order to quantify the impact of inflow water and sediment conditions and reservoir operation mode on reservoir scouring and silting and the fluctuation of Tongguan elevation,the characteristics of reservoir erosion and deposition and variation of Tongguan elevation were analyzed using the measured data of runoff and sediment load and cross-sectional surveys in the reservoir area from 1974 to 2018.A conceptual mode for the equilibrium state of the reservoir channel and Tongguan elevation was proposed.Based on this mode and the delayed response model,calculation methods for the cumulative sediment deposition volume in the reservoir and Tongguan elevation were proposed.These methods consider the impacts of inflow discharge,sediment load and pool level.The influence of different water and sediment conditions and“318 Operation”on erosion and deposition in the reservoir area and Tongguan elevation were quantitatively analyzed.Results showed that the increase of water discharge was the main driving factor for the lowering of the Tongguan elevation,while the increase of water discharge,decrease of sediment load and the decrease of critical discharge to open all the sluice gates in flood season,to some extent,all contributed to the reservoir degradation after 2003.The“318 Operation”,on one hand,decreased the critical water discharge to sluice sediment during flood season,which caused Tongguan elevation to drop by approximately 0.08 m and the reservoir to erode by about 0.024 billion m^3.On the other hand,nevertheless,“318 Operation”increased the average pool level during non-flood season,which resulted in the rise of Tongguan elevation by about 0.03 m and the increase of aggradation volume in the reservoir by 0.024 billion m^3.Therefore,the effect on lowering Tongguan elevation and eroding the reservior channel by reducing the critical water discharge for sluicing was to some extent offset.