Low impact development (LID) is generally regarded as a more sustainable solution for urban stormwater management than conventional urban drainage systems. This study used watershed modelling to evaluate the capability of LID techniques to mitigate the impact of urbanization on hydrology using a catchment area in the city of Toronto, Ontario as a case study. Two rainfall events, with the depths of 60 mm and 101 mm respectively associated with 5 and 100 year storm events, were developed to determine action flood and major flood. The performance of LID elements such as rain barrel/cistern, bioretantion areas, and rain garden on flood attenuation was assessed as retrofitting technologies in the study watershed. Scenarios consisting of the watershed existing condition and different percentages of implementation of rain barrel/cistern, bioretantion areas, and rain garden were evaluated using a proposed LID modeling framework. Results are consistent with those reported in published papers and demonstrate that LID practices have the potential to minimize the undesirable hydrologic effects of urbanization not only in new developments but also in a retrofit application. The study provides an insight into flood management with LID practices in existing urban areas.
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