Strategic emplacement of BMPs in an urban drainage system: A case study in the Montreal area

The need to provide adequate water-quality control using Best Management Practices (BMPs) requires accurate modeling in order to determine their ideal emplacement within the watershed. A case study in the Montreal area using PCSWMM software analyzed the implementation of green roofs, rain gardens, pervious pavement and vegetative swales, as well as their possible combinations by comparing both outfall hydrographs and pollutant removal rates to asses the performance of each alternative. From the individual practices, rain gardens provided the highest levels of runoff control, with slight improvements when coupling them in series with green roofs, but lower performance when adding pervious pavements. Removal rates appear to be more dependent on the infiltration achieved than the actual removal rates. The overland flow-path could significantly impact which pollutants are picked up by runoff, but accurately modeling complex build-up/washoff processes requires information that might not be readily available for all watersheds. Even tough results could be highly case-specific, the results obtained highlight the limitations still faced by water-resources professionals, and raise important points that challenge common conceptions regarding BMP implementations. More data on real-life performances over long periods of time is still needed to better analyze BMPcombinations.