集水区丰水期河流-地下水相互作用机理研究

Frequent precipitation occurs in river catchments during wet seasons. Connected river-groundwater systems can redistribute water effectively, accelerate the mixing of solutes, and improve the functioning of ecosystems. Hence, it is critical to understand river-groundwater interactions during wet seasons thoroughly. This project chooses a typical river catchment of the Hailiutu River in the Ordos Basin as a study site. It will perform systematic and quantitative assessments of the effects of precipitation infiltration and river flood processes on river-groundwater interactions through field work and numerical modelling. In-situ river tracer tests and long-term monitoring will be conducted using multiple tracing techniques. Field-based river-groundwater models will be constructed using a fully coupled physically-based numerical modelling technique. The project will particularly focus on the propagation of groundwater pressure waves and river pressure waves generated from river infiltration and river floods, respectively, and the response times and mechanisms of river-groundwater exchange fluxes, water chemistry at the river-groundwater interface and groundwater percentages in river discharge to the propagation of different pressure waves. In addition, this project will identify key parameters for the river-groundwater exchange fluxes, water chemistry at the river-groundwater interface and groundwater percentages in river discharge through fully coupled river-groundwater models, and examine their similarities and differences. It is anticipated that this project will significantly improve our understanding of the water cycle between surface water and groundwater and provide more accurate hydrodynamic models for contaminant remediation and environmental planning.

河流上游集水区丰水期雨量充沛，连通的河流-地下水系统能够有效再分配水资源，加快物质混合，提高生态系统活力，因此认清集水区丰水期河流-地下水相互作用至关重要。本项目拟选择鄂尔多斯盆地海流兔河一典型集水区为研究对象，利用多种水流示踪技术开展野外原位示踪试验和长时间监测，利用基于物理过程的全耦合模拟技术构建数值模型，系统全面地研究降雨入渗补给和河流洪峰传播过程对河流-地下水相互作用的影响。重点研究降雨入渗引起的地下水压力波和河流洪水引起的地表水压力波传播过程，及河流-地下水界面通量、界面水化学及河流中地下水比例对不同压力波传播的响应时间和响应机制。本项目还将通过河流-地下水全耦合模型，识别河流-地下水界面通量、界面溶质浓度及河流中地下水比例的关键参数及相似与不同点。本研究将深刻提升我们对丰水期河流-地下水系统水文循环的认识，为污染修复、生态环境规划提供准确的水动力学模型。

集水区是流域水资源的重要来源，认清集水期地表水-地下水相互作用具有重要意义。项目构建了多尺度数值模型，揭示了短时强降雨引起的土壤和地下水压力波传播过程及界面通量变化过程，阐明了压力波能够传递到地下水中并最终导致河岸带地下水的快速排泄；开展了不同气候影响下的地表水-地下水相互作用研究，揭示了稳定气候条件下集水区的地表水-地下水相互作用兼具季节变化性和长期稳定性，并提出了变化气候条件下地表水-地下水相互作用变化迅速但是地下水年龄变化具有滞后性和持久性；开展了系列数值实验，分析了集水区河道洪水波引起的河道水化学相对河道水位变化过程，查明了水化学变化的滞后性与压力波的波高和波长成正相关关系，发现了摩擦阻力和坡度对水化学变化滞后时间的影响相反，阐明了土壤类型、含水层的渗透系数及补给等参数对滞后时间的影响较小；选取了位于鄂尔多斯高原的海流兔河流域为研究区，开展了多次原位水化学与同位素监测，构建了三维全耦合数值模型模拟地表水-地下水相互作用过程，认识了多物理过程耦合作用下河流-地下水交换过程，初步查清了地下水压力波及流域蒸散发是复杂条件下河流-地下水交换通量的关键影响因素。项目研究成果可为集水区环境修复、水资源管理提供技术支撑。

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