Department of Earth Sciences, University of Toronto, 27 King's College Circle, Toronto, ON M5S 1A1, Canada; Department of Geography and Environmental Studies, Toronto Metropolitan University, 350 Victoria St, Toronto, ON M5B 2K3, Canada.
Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Scarborough, ON M1C 1A4, Canada.
Water Res. 2024 Nov 15;266:122333. doi: 10.1016/j.watres.2024.122333. Epub 2024 Aug 24.
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.
城市雨水管理系统，特别是雨水下水道，对于管理城市地区的径流至关重要。这些系统旨在潮湿天气事件期间运行；然而，对这些系统的现场观测表明，它们在干燥天气条件下也可能是活跃的水流路径，最终导致水流。与废水系统中的干季流不同，雨水下水道干季流尚未得到充分探讨。本研究使用水中的氧和氢稳定同位素来检查高度城市化流域中雨水下水道干季流的来源。稳定同位素混合模型应用于两个雨水集水区的出水口和位于加拿大多伦多的接收黑溪。研究结果表明，在干旱时期，雨水下水道从自来水、废水和地下水以及一些降水接收非雨水输入，这些来源在流域尺度上可能构成黑溪流量的 19%。对黑溪和出水口的流量和水源进行了季节性模式观察。在一个出水口，整个春季、夏季和秋季，雨水下水道的干季流主要来自供水系统（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，而地下水和供水系统在秋季的比例相等。黑溪基流是水源的动态混合，有时与雨水下水道出水口观察到的水源相似。考虑到这些发现，未来的工作应该包括对其他出水口进行战略采样，并收集多年数据，以探索这些过程的年际变化，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复制类似的研究。研究结果强调，我们对雨水下水道干季流的理解相对有限，这强调了需要进一步探索这一现象，以为城市水文模型、水质研究和城市水资源管理提供信息。
