大型水利工程影响下下游交汇河道演变响应及规律研究

The large-scale water conservancy project can regulate the natural runoff processes, control hydrology and fluvial processes of the downstream rivers, affect processes of flow and sediment encountering at the downstream river confluences, and further influence flow and sediment transport and morphological processes of the tributaries. Previous studies have paid much attention to the influence of the large-scale water conservancy project on the downstream main river, but the knowledge of response of unsteady flow and sediment encountering and fluvial processes of the tributaries to the operation of the water conservancy project is sparse. The discussions on the mechanisms and the reveal of universal theories are desired. This proposal intends to focus on the river confluences downstream a large-scale water conservancy project, and the response of their flow-sediment-morphological processes to the project's operation. Based on field observations, laboratory experiments, numerical simulations and theoretical analysis, we attempt to study the temporal and spatial evolution of flow and sediment and fluvial processes of the main river downstream the large-scale project, the flow and sediment fluxes and response of bed morphology at river confluences with unsteady flow and sediment discharges, and the mechanism of the main river's blocking effect on the tributary and its controlling factors, aiming to reveal the response of fluvial processes of river confluences to the upstream large-scale project. The results can provide theoretical and technological supports for treatment of the tributaries of the Yangtze River downstream the Three Gorges Project, such as the regulation of Poyang Lake and Dongting Lake and the construction of the Poyang Lake Control Project. They shall have a good application prospect.

大型水利工程的运行是对天然径流过程的控制，决定着下游干流的水文情势和河道演变，影响沿线各交汇口水沙遭遇过程，从而影响入汇支流的水沙运动及河床变化。国内外研究更多地关注大型水利工程对下游干流的影响，工程调蓄影响下下游非恒定水沙交汇及支流水-沙-河床变形响应方面的研究比较局限，缺乏机理层面的探讨和普适性规律的揭示。本项目拟以大型水利工程下游交汇河道为研究对象，以工程调蓄和河道水-沙-河床冲淤响应为主线，利用现场观测、室内试验、数值模拟和理论分析等多种手段和方法，开展大型水利工程下游河道水沙时空演变机制及河床变化特征、干支流非恒定交汇的水沙通量过程及河床变形响应机制、干支流顶托机理及其驱动机制等方面研究，最终揭示大型水利工程影响下下游交汇河道演变响应及规律。研究成果为进一步开展三峡水利枢纽工程下游长江各大支流治理（如两湖调控与湖控工程的建设）方面的研究提供理论和技术支撑，具有很好的应用前景。

大型水利工程的运行是对天然径流过程的控制，决定着下游干流的水文情势和河道演变，影响沿线各交汇口水沙遭遇过程，从而影响入汇支流的水沙运动及河床变化。国内外研究更多地关注大型水利工程对下游干流的影响，工程调蓄影响下下游非恒定水沙交汇及支流水-沙-河床变形响应方面的研究比较局限，缺乏机理层面的探讨和普适性规律的揭示。本项目采用现场实验、室内实验和数值计算，选择三峡工程下游长江与鄱阳湖交汇处为研究对象，研究大型水利工程影响下下游交汇河道演变响应及规律。主要结果如下：（1）通过分析资料和现场观测，发现三峡运行后江湖交汇处长江一侧河床发生明显下切，而对鄱阳湖一侧河床则影响较小；（2）提出了大尺度交汇中流线弯曲和主流侵入支流共同作用下的二次流形成机制，推翻了传统观点认为大尺度河道交汇无法产生二次流的传统认知；（3）揭示了二次流加速/阻碍对泥沙掺混的作用机理，阐明了交汇处河床局部地形在不同二次流模式影响下的演变过程；（4）利用现场实验，发现交汇处来流的泥沙输移模式是影响江河交汇处河道地形演变的重要控制因素；（5）利用精细水槽实验，对复式河道交汇区的水流结构进行了研究，提出主汊对支汊的入侵是导致剪切层倾斜、二次流强度增强以及分离区宽度增加的主要原因；（6）使用分离涡数值模拟方法，建立了长江-鄱阳湖交汇口三维数值模型，发现影响两汊掺混的主要水流结构为大尺度二次流单元，而非在小型交汇流中发现的流向涡，揭示了温差引起的密度差效应对大型现场交汇流掺混特征的影响。