This study presents high-resolution flow-through experiments investigating transport processes in a laboratory setup mimicking an aquifer affected by hydropeaking (i.e., abrupt fluctuations in the river stage by the release or storage of water in reservoirs). Highly transient flow conditions were experimentally generated by sudden changes of the water level in two rivers in hydraulic contact with an unconfined aquifer. High-resolution image analysis and depth-resolved, high-frequency sampling at the outlet allowed monitoring of the spatio-temporal evolution and the breakthrough of a dye tracer plume in the porous medium. The plume spreading and mixing were quantified by moment analysis and entropy-based metrics of the scalar field. We show that hydropeaking strongly enhances spreading and mixing in the subsurface (up to 249.5% and 41.8% in these experiments) and demonstrate the relevance of considering highly transient flow regimes to properly capture transport and mixing-controlled biogeochemical reactions at the surface water - groundwater interface.

中文翻译：

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受水峰影响的含水层中的混合增强机制：来自流通实验室实验的见解

本研究展示了在模拟受水峰影响的含水层（即，由于水库中水的释放或储存而导致河流水位突然波动）的实验室设置中研究运输过程的高分辨率流通实验。通过与非承压含水层水力接触的两条河流中水位的突然变化，实验产生了高度瞬态流动条件。出口处的高分辨率图像分析和深度分辨、高频采样允许监测多孔介质中的时空演变和染料示踪羽流的突破。羽流扩散和混合通过矩分析和标量场的基于熵的度量来量化。我们表明，水峰化极大地增强了地下的扩散和混合（高达 249.5% 和 41.