Abstract The treatment efficiency of constructed wetlands is strongly related to hydraulic conditions. The occurrences of a dead zone and short-circuiting flow decrease flow uniformity and might decrease hydraulic performance. This study aims to investigate the relationship between spatial flow characteristics and wetland treatment performance. A hydrodynamic and contaminant transport model conducted ten sets of simulations with different water depths and five sets of simulations with varying numbers of emergent obstructions. Each experiment had a variant number, dimension, and allocation of obstructions. A metric of flow uniformity was proposed and discussed. We demonstrated how the dead zone and short-circuiting alter flow conditions and affect the hydraulic performance and pollutant treatment efficiency by examining the flow characteristics. The order-of-magnitude of time scales between the advective transport rate and diffusive transport rate was analyzed by calculating the Peclet number. The first-order model was used to calculate the pollutant removal ratio. The results revealed that the values of advection were approximately tens to hundreds of times those of diffusion, indicating that the flow velocity dominated the dispersion behavior. The significant improvement in flow uniformity was found when emergent obstructions were installed. The index value of the dead zone was 2 to 69 times that of the short-circuiting flow, which shows that the dead zone significantly affected the uniformity of the flow. In addition, we discovered that when the coverage ratio of the dead zone was less than 50%, the hydraulic efficiency increased from 0.55 to 1.00. Nevertheless, the short-circuiting flow was found to have minor effects on the hydraulic efficiency. The new methodology for distinguishing dead zones and short-circuiting flow areas is useful for evaluating hydraulic performance directly instead of executing water quality modeling or tracer experiments.

中文翻译：

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用于量化人工湿地水力和处理性能的流量均匀性指标

摘要 人工湿地的处理效率与水力条件密切相关。死区和短路流的出现降低了流动的均匀性，并可能降低水力性能。本研究旨在探讨空间流动特征与湿地处理性能之间的关系。水动力和污染物传输模型进行了十组不同水深的模拟和五组不同数量紧急障碍物的模拟。每个实验都有一个变体编号、维度和障碍物的分配。提出并讨论了流动均匀性的度量。我们通过检查流动特性展示了死区和短路如何改变流动条件并影响水力性能和污染物处理效率。通过计算 Peclet 数，分析了平流输运率和扩散输运率之间时间尺度的数量级。采用一阶模型计算污染物去除率。结果表明，平流值大约是扩散值的几十到几百倍，表明流速主导了弥散行为。当安装紧急障碍物时，发现流动均匀性有显着改善。死区的指标值为短路流的2～69倍，说明死区对流的均匀性有显着影响。此外，我们发现当死区覆盖率小于50%时，水力效率从0.55提高到1.00。尽管如此，发现短路流量对水力效率的影响很小。用于区分死区和短路流动区域的新方法可用于直接评估水力性能，而不是执行水质建模或示踪实验。