Hydrologic performance of grass swales in cold maritime climates: Impacts of frost, rain-on-snow and snow cover on flow and volume reduction

Autor: Hrund Ólöf Andradóttir, Tarek Zaqout
Rok vydání: 2021
Předmět:
Zdroj: Journal of Hydrology. 597:126159
ISSN: 0022-1694
DOI: 10.1016/j.jhydrol.2021.126159
Popis: Sustainable urban drainage solutions (SuDS) are a diverse set of design options that mitigate floods and improve water quality. Grass swales are the sole component of SuDS that transports runoff over long distances to downstream recipients. A deeper understanding of the performance of grass swales in different winter conditions is important in order for cities to achieve a greater climate resiliency. The goal of this study was to assess the impacts of frequent rain-on-snow, and freeze–thaw cycles on the hydrologic performance of grass swales. A total of 63 field synthetic runoff experiments were performed in a 5.8 m long section of a grass swale in the Urriðaholt neighborhood, Gardabaer, Iceland over 18 months. A three-fold reduction in peak flow attenuation was observed in winter (avg. 13%) compared to summer (avg. 38%) for hydraulic loadings ranging between 19 and 131 cm/h. The reduction in the performance of the swale was primarily due to frost formation and secondarily due to snow. The frequent rainfall, snowmelt, and rain-on-snow events elevated the soil water content and rendered the swale media susceptible to frost formation. The formation of pore ice within the 5 cm soil horizon led to a considerable reduction in soil porosity, which negatively affected the infiltration capacity, and shortened runoff lag times. Snow affected the performance by concentrating the flow in narrow channels, which reduced the effective area of infiltration, but also led to longer lag times and stored a portion of the runoff water within its pack. Despite the deterioration in the swale’s efficiency in winter, infiltration was observed in all synthetic runoff experiments, indicating that frost was either porous/granular, or heterogeneous in nature. The swale served its purpose to moderately reduce runoff peaks and volumes, especially for small and medium events. This research highlights the importance of effectively draining infiltration-based systems in cold climates to avoid the adverse effects of low temperatures.
Databáze: OpenAIRE
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