Climate and geographical influence on the performance of infiltration-based facilities for managing runoff – Temporal and spatial variability

Sammanfattning: Climate change is expected to lead to more intense and severe rainfall events in the future, significantly increasing the risk of urban flooding. This change, characterized by spatial and temporal shifts in precipitation patterns, presents a challenge to the capacity of existing urban drainage systems, which may lead to higher runoff volumes than they were initially designed to handle. Relying solely on enlarging stormwater infrastructure to tackle this issue could be expensive and may transfer the flooding risk downstream, rather than effectively resolving it. Furthermore, climate change may also lead to prolonged dry spells, potentially resulting in soil compaction and diminished soil infiltration rates. Given these considerations, it is essential to ensure urban drainage systems are both adaptable and space-efficient, with an enhanced capacity to manage the heightened rainfall caused by climate change. As awareness of the hydrological and environmental impacts of urbanization on catchments grows, there has been a paradigm shift toward adopting green infrastructure solutions. These approaches diverge from traditional 'end-of-pipe' strategies, emphasizing more holistic and sustainable methods. The overall aim of this thesis is to investigate the implications of climatic conditions and geographic location on the retention and detention capacity of three types of infiltration-based facilities: a biofilter cell, a green roof, and a grass swale. A rainfall-runoff model of a biofilter cell and a green roof, combined with swale irrigation experiments, was used to evaluate the capacity of these facilities to reduce runoff volumes and attenuate peak flows. The analysis was conducted in four urban areas representing oceanic (Cfc), humid continental (Dfb), and subarctic (Dfc) climatic zones. The assessment also includes the effect of temporal and spatial variation of saturated hydraulic conductivities (ksat). Swale irrigation experiments were conducted to evaluate the effect of outflow controls on swale retention and detention capacities, under high soil moisture conditions. Results for biofilter cells and green roofs showed that retention capacities were influenced by the combined effect of antecedent wetness, the extent of winter periods, and the frequency and intensity of rainfall events. Conversely, green roofs were found to have a higher sensitivity to initial soil conditions and antecedent dry weather periods, which was observed through a spread distribution of runoff volume reductions. Grass swales exhibited a large spatial distribution of hydraulic conductivity (ksat) values, with lower values at the swale bottom and higher values at the slope on the right side. Results from a full-scale infiltration test showed that overall, grass swale infiltration capacities are representative of the measured ksat values at the swale bottom. Finally, the presence of outflow controls was observed to enhance the retention and detention capacities of grass swales, even under high levels of soil moisture content. This increase in swale hydrological functionality was influenced by swale outflow controls, leading to greater utilization of the grass swale surface area. Differences between swales with outflow controls and those without were noted due to the effect of the additional storage capacity provided by an outlet control weir. Conversely, it was shown that swales without outflow controls experienced limited retention under high soil moisture content, restricted by the finite capacity of surface depression storage.