Evaluating Nature-Based Solutions for Urban Flood Resilience in Ottawa, Canada

Increasing trends in impervious surfaces, coupled with intensification of precipitation extremes due to future climate change, can potentially exacerbate flooding risks in metropolitan areas. As traditional grey infrastructure struggle to adapt to these challenges, nature-based solutions (NBS) are gaining attraction as adaptation strategies to complement traditional solutions. This study investigated NBS efficacy, focusing on bioretention cells as adaptive measures for flood mitigation in Ottawa's west end neighborhoods. Two coupled 1D-2D PCSWMM models, developed by The City of Ottawa, were evaluated for two flood-prone areas, generally matching in size, land use, and key attributes such as soil layer characteristics, flow routing and simulation settings, and the general approach to modeling. The effectiveness of bioretention cells in mitigating surface flooding was assessed for each neighborhood, considering various precipitation events, ranging from 2- to 100-year return periods. While highly effective in one area with up to 85% runoff volume reduction, bioretention cells exhibited comparatively limited efficacy in the other neighborhood, reaching no higher than 35%.

The findings of this study regarding effectiveness disparity highlight limitations of NBS, emphasizing the need to consider factors such as area characteristics, and land use when designing NBS. The study also investigated NBS design complexities, raising questions about their universal applicability and effectiveness. By examining NBS interplay with each area's attributes, this research contributes towards improving understanding of nature-based approaches for flood mitigation in urban regions.