考虑极端干旱应急需水的水库分级旱限水位动态控制

    Controlling drought-limited water level in the reservoir using emergency water under extreme drought

    • 摘要: 为应对极端干旱下区域水资源可用量骤减、骨干水库抗旱供水任务大幅增加,且常规调度难以满足需求的问题,该研究以河北省王快、西大洋水库及沙河、唐河灌区为例,考虑极端条件下需水突增的特殊情景,设计常规与极端干旱情景下供需边界,进而计算水库常规-特殊旱限水位并制定可动态切换的分级旱限水位控制规则,同时通过设置多方案对比分析其在特枯水年和典型连枯年中的调控效果。结果表明:王快水库和西大洋水库应用常规-特殊旱限水位后,沙河灌溉和唐河灌溉在特枯水年缺水状况得到明显改善,缺水量分别减少了6653万m33245万m3;在典型连枯年内,水库通过提前存蓄,使得沙河灌溉和唐河灌溉严重缺水时段的供水保障率由不足10%分别提升至约90%和50%,极端破坏过程转变为宽浅式破坏,有效降低了严重缺水风险,提升了农业灌溉保障水平。研究成果可为水库抗旱决策和极端干旱条件下的应急管理提供科学支撑。

       

      Abstract: Available water volume from the regional sources is ever declining sharply under extreme drought. While the drought-relief water-supply tasks can be assigned to rapidly increase the major reservoirs. However, the conventional reservoir operation cannot fully meet these harsh demands in recent years. It is often required for the high effectiveness of drought-response, in order to buffer the severe water-supply shortages. In this study, a demand-oriented perspective was adopted to distinguish between normal and extreme drought scenarios. A graded drought-limited water level (DLWL) was dynamically controlled to consider the historical supply-demand patterns and abrupt surges in the water demand during extreme events. Three primary steps were set: (1) To define the supply-demand boundaries for the different drought scenarios, according to the water-use patterns and long-term hydrological statistics, (2) To calculate the regular and special DLWLs that represented the minimum storage thresholds for the normal and extreme drought demand, respectively, and (3) to formulate the dynamic control for the switching between the regular and special DLWLs, according to the drought severity, reservoir storage evolution, and the projected surges of the water demand. A case study was conducted for the Wangkuai and Xidayang reservoirs, as well as the Shahe and Tanghe irrigation districts in Hebei Province, China. The regular-special DLWL was calculated to develop a dynamically switchable strategy of the graded DLWL control, in order to guide the drought-response operations. The regular DLWL mode was applied to the normal drought conditions, in order to fully meet the water supply for the urban domestic use, agricultural irrigation, and ecological baseflow. The special DLWL mode was activated under extreme drought. The urban domestic water supply was prioritized to moderately restrict the agricultural irrigation, and then further limit the ecological water use. Three scheduling schemes (baseline scheme, rugular scheme and proposed scheme) were implemented for the comparative analysis. The evaluation was focused mainly on the extremely dry years and typical multi-year dry periods. The results indicate that the regular-special DLWL scheme was applied to substantially mitigate the water shortages in the extremely dry years. Specifically, the total water shortages decreased by 66.53 and 32.45 million m3, respectively, in the Shahe and Tanghe irrigation districts. The earlier strategic storage triggered by the special DLWL markedly improved the water supply guarantee rate during several severely impacted periods in the typical consecutive dry years. There was also an increase from below 10% to approximately 90% and 50%, respectively. The irrigation shortages declined by 186.20 and 182.74 million m3, respectively, over the multi-year droughts. Furthermore, the number of months with the severe shortage decreased by 7 and 32 months, respectively, effectively alleviating the deficits. There was a decrease in the frequency and duration of acute water-stress episodes. Moreover, the approach was more effective in transforming the extreme shortage into a wider and shallower shortage pattern. The incidence of the high-intensity shortage episodes was also reduced to lower the risk of severe shortages. The guarantee rate for agricultural irrigation was improved after optimization. The findings can also provide scientific support for the reservoir drought resistance and emergency decision-making under extreme drought.

       

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