GREEN ROOF WINNIPEG

Funded by the FCM grant, the City of Winnipeg explored the feasibility of developing a green roof strategy for flat-topped buildings in its downtown area. Such a strategy could help alleviate stormwater management problems in Winnipeg’s downtown. The City felt that a green roof strategy could be incorporated into the Combined Sewer Overflow (CSO) control model to reduce runoff effects and provide other environmental benefits.
The Assiniboine district was the focus of this study due to its high concentration of flattopped buildings. The area is also the most prone to overflows from the combined sewer system. Recent aerial photographs and visual inspections indicated that an area of 218,773 square metres (almost 20% of the total area of the district) could be used for green roof development.
Control-system models were created to simulate rainfall and runoff during a typical year. Various scenarios were examined to determine whether a green roof strategy could reduce not only the number of overflows in a year, but also their volume and the volume of wastewater going to the water pollution control center.
In this study plant species were also evaluated for their carbon-fixation and sequestering potential.
Data collected during the stormwater modeling process indicated that the number of overflows could be reduced by 16%, if 100% of the potential roof space in the district were used. The volume of the overflow could also be reduced by approximately 48%, which in turn would cut the volume of flow to the water pollution control centers. In terms of the carbon fixation it was found that if 100% of the potential green roof space were developed, 24.5 tonnes of carbon would be fixed (removed) annually.

--chris c.--