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WELCOME
Green roofs are one aspect of sustainable design that can be implemented and have an on-going positive effect on the community from increasing the amount of useable green space in urban areas to increasing the rate at which the air is purified of harmful toxins.
For
Winnipeg
specifically, developing a green roof strategy has the potential to augment the City's combined sewer overflow management plan including aiding in pollution control and basement flooding prevention.
Winnipeg
has a combined sewer system for a large percent of its area and during spring thaw and heavy rain the capacity of the system is surpassed. The excess rainwater and sewage overflows into the Red and
Assiniboine
Rivers
, a direct result of the fact that our combined sewer system is unable to deal with the amount of runoff at those times. Green roofs are able to hold an incredible amount of water and thereby delay runoff, reduce the runoff rate and reduce the runoff volume. A study cited by Peck (2000) for the City of
Portland
found that if half of the buildings in the downtown area had green roofs, the equivalent of two hundred and nineteen acres, an estimated sixty-six million gallons of water would be retained annually. This would eliminate combined sewer overflows in their city by seventeen million gallons. The study concluded that storm water discharges would be reduced by 11-15%. Most city centers are primarily constructed of impermeable surfaces and when it rains, eighty to eighty-five percent of that is directed to stormwater drains while the remainder evaporates. None is absorbed by the surfaces themselves. A green roof has the ability to retain forty to seventy percent of the rainwater that falls upon it and release it over time. This would result in lower combined sewer overflows in the City of
Winnipeg
and enhance the quality of our rivers and streams. Neil Cunningham (2001) states that "the widespread application of green roofs could also serve to decrease our dependence on costly infrastructure such as sewage treatment plants" (94), which with the mishap at The City of Winnipeg's North End Sewage Treatment Plant we are in great need of.
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