水库下泄低温水对潜流带及临近包气带水温环境影响机理及模型研究

Assessing the temperature changes occurring in both hyporheic zone and bank vadose zone is critical although it is likely to be more important than other factors. As metabolic activity within streambed may be strongly affected by the thermal regime of the stream water, and also plenty of literatures have already showed that the surface water temperature may be changed greatly by the low temperature water (LTW) discharged from the lower part of a deep reservoir; especially the elevation of water-intakes of electronic station is within the mid-lower layer of deep reservoirs. In China, it is still lack of effect on the analysis of the impacts of temperature variations and water environment changes in the riverbed. This may be not conducive to the ecosystem assessment of the downstream under full range scale. Herein, we intend to select a typical reservoir and its downstream as our field research object, and also flume experiments will be carried out for further investigation on the mechanism of thermal dispersion in both hyporheic zone and river bank vadose zone. Our purpose is trying to make clear on the eco-driving factors and driving force of hydrothermal process, and fully reveal the mechanism of water and heat conversion in the surface-hyporheic-subsurface structure, the hydrothermal dispersion discipline in bank vadose zone on various spatial and temporal scales. Then, based on the former works, we intend to establish the corresponding temperature environment assessment models, develop the theoretical analysis methods and experiment research technologies. And finally, put forward the key assessment indicators that can be used for evaluate the impacts on riverbed ecosystem due to the LTW discharged from up reservoir. The results not only can be used for quantitative assessment of the ecological environment around the riverbed zones, but also can be of great significance for the river ecosystem reconstruction and restoration.

河道水温环境变化影响下的温度环境变化和生态结构效应是当今水环境科学的前沿课题。受大型水库下泄低温水影响所带来的河道水力条件改变和温度变异形成了对河床区（潜流带及临近包气带）生境结构和温度环境的强烈冲击。在我国尚缺乏针对大型水库下泄低温水影响下的河床区温度变异和水环境效应评估模型。本项目拟选择典型水库及下游河流，通过室内外试验、理论研究和数值分析等综合方法，开展下泄低温水对潜流带及临近包气带内水温环境影响机理及评估模型研究。分析影响生态水热过程的驱动因子和驱动力，全面揭示地表-潜流带-地下三元结构水热迁移转化机制及受侧向潜流交换影响的包气带内水热时空分布规律，建立和发展复合时空尺度的河床区水温环境评估模型、理论分析方法及试验研究技术，并提出相应的环境评估指标。研究成果不仅可用于定量评估下泄低温水对河床区水温生态环境影响效应，对恢复和重建正遭受破坏和已退化的河流生态格局也具有重要的意义。

低温水泄入下游河道沿程流动并与河床潜流带及临近植被覆盖区进行热量及潜流水交换，使得河床周边一定范围内岩土体形成与天然状态相异的温度分布格局，导致潜流带和临近包气带中水分场及温度场发生改变，并直接对依存其中的底栖动物、水生植物、微生物群等生存环境（尤其是温度环境）产生影响。本课题通过现场试验、室内试验和数值分析等综合方法，开展了水库下泄低温水对潜流带及临近包气带内水温环境影响机理及评估模型研究。研究成果揭示了水库下泄低温水在不同季节对河岸带地下水流场和温度场的影响规律，对在太阳辐射和低温河水双向作用下河岸潜流水流动及温度分布具有的特殊性有了更深入的认识；探明了受外界多向温度影响，土体中水温维持、扩散、恢复等规律，建立了水位、流量与潜流交换速率、交换深度的关系；定量分析了床面几何形态对潜流交换的影响，发现河床形态起伏、强非均质性及强渗透性能很好地促进潜流交换速率，并使得地表溶质颗粒相应获得较长的交换路径和较短的平均残留时间，提出了用于判断河床地形与河床区非均质性对潜流交换贡献比重的相对关系无量纲参数N等；研究了不同水动力和沙坡地形形状条件下的潜流交换规律和沙坡附近紊流结构特点，分析了二维、三维模型对水沙界面潜流交换过程影响的差异性，提出了动床阻力与沙波三维交错特征参数之间的经验公式等。本课题取得的研究成果已得到国内外同行的关注。目前课题组正积极准备将研究成果对接实际工程应用，近期拟结合扬州市北城河（叶桥大沟）综合整治工程，开展基于地表水-地下水交换水动力理论的生态河道构建技术研究与应用。