梯级水库对长江枯水期生态水文情势影响的时空尺度效应研究

Cascade reservoirs at the upper reaches are one of the important factors affecting the eco-hydrological regime at the middle-lower Yangtze River. The project aims to study the temporal and spatial scale effect of the impacts of cascade reservoirs on eco-hydrological regime of the dry season at the Yangtze River. The eco-hydrological regime of the dry season is described by a series of hydrological indicators. The evolution rule and characteristics of the hydrological regime of the dry season at the Yangtze River are analyzed. A one-dimensional hydrodynamic model of the stem stream is constructed to simulate the flow processes at the middle-lower reaches influenced by the cascade reservoirs. Considering the deficiencies of the existing assessment methods of hydrological regime alteration, a new method is proposed and applied to assess the hydrological regime alteration of the dry season influenced by cascade reservoirs. The accumulative impacts of cascade reservoirs on the hydrological features of the dry season at the middle-lower Yangtze River are studied considering the scenario in which the built, being built and planned to be built reservoirs are all in operation. The temporal scale effect of the cascade reservoir influence is studied by comparing the difference of the characteristic value changes and alteration degree of the hydrological indicators with different duration. The spatial scale effect of the cascade reservoir influence is studied by comparing the change features of the hydrological regime at different locations. The ecological effect of the cascade reservoirs is studied using the newly constructed satisfaction degree indicator of ecological flow and ecological water level. The results will contribute to explicit the influence mechanisms of cascade reservoirs on hydrological regime of the dry season and provide beneficial references for the water ecological civilization construction of the Yangtze Basin.

长江上游梯级水库是影响中下游生态水文情势的重要因素之一，项目拟研究其对中下游枯水期生态水文情势影响的时间与空间尺度效应。采用一系列水文指标描述枯水期水文情势，分析长江枯水期水文情势的演变规律与特征。构建长江干流一维水动力学模型，模拟梯级水库影响下中下游的径流过程。针对现有方法的不足，提出一种新的水文情势改变程度评价方法，将其应用于评价梯级水库影响下枯水期水文情势的改变程度。考虑已建与在建、规划水库全部建成运行的情景，研究梯级水库对长江中下游枯水期水文特征的累积效应。通过对比分析不同历时水文指标特征值变化及改变程度的差异，研究梯级水库影响的时间尺度效应；通过对比分析不同位置控制站点水文情势的变化特征，研究梯级水库影响的空间尺度效应。构建生态流量、生态水位满足度指标，研究梯级水库影响的生态效应。研究成果将有助于明确水库对枯水期水文情势的影响机理，为长江流域水生态文明建设提供有益参考。

河湖水文情势是水生态系统重要的驱动因子，梯级水库群在带来巨大社会经济效益的同时，对水文情势也造成了一定程度的影响。项目针对梯级水库群对长江枯水期生态水文情势影响开展研究：选取长江中下游干流及鄱阳湖湖区主要水文控制站，采用Mann-Kendall非参数统计检验、多时间尺度扫描t检验、Morlet小波分析等方法分析了长江中下游水文情势变化规律及特征；构建了长江干流一维水动力学模型，分析了江湖流量—水位关系，通过情境模拟分析了长江干流流量过程及鄱阳湖水位过程，揭示了长江上游流域及鄱阳湖流域水库群对长江中下游水文特征的累积影响；对比分析了现有主要水文情势改变程度评价方法的优缺点，针对目前主要方法的不足，提出了一种新的水文情势改变程度评价方法直方图比对法（Histogram Comparison Approach），并在评价不同气候区、不同调节能力水库影响下水文情势改变程度中进行了应用研究；分析了枯水期鄱阳湖生态水位及长江干流生态流量，构造了生态水位满足度及生态流量满足度指标，基于情境模拟分析成果，评估了水库群对枯水期生态水位、生态流量的累积影响。研究结果表明：各水文指标在不同的时间尺度下表现出不同的变化特征，且各水文站水文指标的变化特征也有所不同，梯级水库群可能是导致枯水期水文指标变化的主要原因；水库群蓄水使长江干流流量有所降低，其中10月份流量降低幅度最大，水库群枯水期供水使长江干流流量有所上升，其中2月份流量上升幅度最大，而受水库群径流调节、河道冲刷等作用的综合影响，鄱阳湖枯水期各月份平均水位都有所降低，其中10月水位降低幅度最大；水库群蓄水期长江干流生态流量满足度有所降低，鄱阳湖枯水期生态水位满足度均不同程度地有所降低。项目研究成果有助于阐明梯级水库群对长江中下游枯水期生态水文情势的影响机理，完善水文情势改变程度的评价方法，丰富河湖生态需水理论研究，为长江流域水库群优化生态调度提供科学依据，为长江流域水生态系统保护及水生态文明建设提供有益参考。