Urban stormwater management systems, particularly storm sewers, are critical for managing runoff in urban areas. These systems are designed to function during wet weather events; however, field-based observations of these systems suggest that they may also be active flow pathways in dry weather conditions, ultimately contributing to streamflow. Unlike dry weather flow in wastewater systems, storm sewer dry weather flow has not been thoroughly explored. This research used stable isotopes of oxygen and hydrogen in water to examine the sources of dry weather flow from storm sewers in a highly urban catchment. A stable isotope mixing model was applied at the outfalls of two stormwater catchments and the receiving Black Creek, located in Toronto, Canada. Findings suggest that during dry periods, storm sewers receive non-stormwater inputs from tap water, wastewater, and groundwater, along with some precipitation, and that these sources may constitute up to 19 % of Black Creek's flow at the watershed scale. Seasonal patterns in flow and water sources were observed for the Black Creek and outfalls. At one outfall, dry weather flow was predominantly from the water distribution system (i.e., tap water and/or wastewater) throughout spring, summer, and fall. In contrast, at the second outfall, groundwater dominated in spring and summer, and groundwater and water distribution were equally proportioned in fall. Black Creek baseflow comprises a dynamic mix of water sources that at times are similar to the sources observed at the stormwater outfalls. Considering these findings, future work should incorporate strategic sampling of additional outfalls, and multiple years of data collection to explore inter-annual variability in these processes and focus on replicating a similar study in other urban watersheds with different climates and/or water infrastructure design. The study findings highlight that our understanding of dry weather flow from storm sewers is relatively limited, emphasizing the need for further exploration of this phenomenon to inform urban hydrological modelling, water quality studies, and urban water management.

中文翻译：

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在干旱天气期间，对从雨水管系统流向接收河流的水进行基于同位素的源评估


城市雨水管理系统，尤其是雨水管，对于管理城市地区的径流至关重要。这些系统设计用于在潮湿天气事件期间运行;然而，对这些系统的实地观察表明，在干燥天气条件下，它们也可能是活跃的水流路径，最终导致径流。与废水系统中的干燥天气流不同，雨水道干燥天气流尚未得到彻底探索。这项研究使用水中氧和氢的稳定同位素来检查高度城市化集水区雨水管的干燥天气流量来源。在位于加拿大多伦多的两个雨水集水区和接收 Black Creek 的排放口应用了稳定同位素混合模型。研究结果表明，在干旱时期，雨水管从自来水、废水和地下水以及一些降水中接收非雨水输入，并且在流域规模上，这些来源可能占 Black Creek 流量的 19%。观察到 Black Creek 和排污口的流量和水源的季节性模式。在一个排污口，整个春季、夏季和秋季的旱季流量主要来自配水系统（即自来水和/或废水）。相比之下，在第二个出水口，地下水在春季和夏季占主导地位，而地下水和水的分配在秋季比例相等。Black Creek 基流由水源的动态组合组成，有时与在雨水排放口观察到的水源相似。 考虑到这些发现，未来的工作应包括对额外排放口的战略采样和多年的数据收集，以探索这些过程中的年际变化，并专注于在具有不同气候和/或水基础设施设计的其他城市流域中复制类似的研究。研究结果强调，我们对雨水管道干燥天气流量的了解相对有限，这强调了进一步探索这一现象的必要性，以便为城市水文建模、水质研究和城市水资源管理提供信息。