Model-based Assessments of Smart Blue Roof

Smart blue roofs (SBR) offer potential to relieve downstream infrastructure of wet weather flows by holding a few cm of rainfall, which can be released strategically and/or retained on-site for reuse. Their application and modelling haven’t received much attention to date, and a project to better understand their performance through monitoring is currently underway, in collaboration with the Credit Valley Conservation. This paper presents several modelling approaches that have been developed and tested in an effort to better understand both the individual operation and performance, and the potential cumulative impacts of SBRs as a retrofit option in an urban drainage system. On a neighbourhood and street-scale, SWMM modelling and the Rational Model were developed to understand the impacts of SBRs on the sizing and longevity of downstream infrastructure, respectively, accounting for future climate projections. The modelling results indicate a significant potential of SBR implementation to reduce the sizing of downstream stormwater management ponds, resulting in the recovery of developable land. On the conveyance systems side, SBRs show the potential to extend the acceptable service life of storm sewers, even for systems that were undersized in their original design. These models, however, were event-based, and the current research is focused on detailed, mass-balance modelling of SBR deployment in combination with rainwater harvesting on individual buildings. Since modelling the evaporation process at small spatial and temporal scales is important for SBRs, development and calibration of an hourly evaporation model is underway that will be integrated into a high-resolution water balance framework and linked to SWMM for continuous simulation and exploration of control strategies.