Analyzing the hydrological behaviour of bioretention cells: insights from field data and SWMM modelling

Abstract

Bioretention cells (BRCs) are widely implemented in urban areas to manage stormwater runoff and reduce pressure on drainage systems. However, their actual performance often diverges from design expectations due to construction constraints and site-specific conditions. This study compares water retention in 31 BRCs located in Montreal, Canada, as simulated with the Storm Water Management Model (SWMM) and observed through field data collection. BRCs were selected for analysis based on their impervious-to-permeable (I/P) ratio and physical characteristics. The field data comprised water level measurements taken by pressure probes and rainfall data provided by the city, used to analyze the hydrological behaviour of the BRCs during the non-freezing season (May to November). Results for four randomly selected BRCs are presented herein. For one of them, the simulated and observed water retention were close, with a Nash-Sutcliffe efficiency value of 0.74 and a strong positive correlation. For the other three, differences were observed between modelled and observed data, attributed to deviations between design (modelled) and field-built conditions, as confirmed by field visits during rainfall events. These results highlight the need to consider the physical limitations of the BRCs in the field and their construction characteristics, such as elevated inlets or poorly directed street slopes, when assessing their performance.