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Stormwater Management

Calculated results show that existing impervious surfaces on the selected residential lot generate a total of 98m³ of runoff per year. The addition of a laneway house on the selected lot raises the amount of impervious roof surface by 12% and paved surface by 7%. Results show that this increase in impervious surfaces augments the annual runoff volume by 56m³, with 37m³ from roof (50m²). Using an extensive green roof on a laneway house can reduce the roof runoff by 8m³ (22%) per year. With additional water storage systems, such as polyethylene tanks, another 13m³ can be retained for irrigation.


Climatic Factors

Previous research from cities around the world has shown that extensive green roofs can significantly reduce the quantity of stormwater runoff. However, results also show that the total annual runoff reduction achieved by extensive green roof also could vary significantly, from 29% in Vancouver, BC, to 47% in Augustenborg, Sweden, and 74% in Washington, DC. The efficiency of green roof as stormwater a management tool is strongly related to local climatic conditions, and the climatic elements that most influence the eventual runoff reduction of green roofs are rainfall, evapotranpsiration and temperature. The intention of this study is to find out which climatic elements most influence the eventual runoff reduction of green roofs, and then to develop a ranking system of climatic factors which could be used in estimating the potential of green roof on reducing stormwater runoff.




Green Factor

Green- factor systems, rating the “ecological value” of a site and the green factors for landscape elements according to their positive effects on the ecosystem, are adaptable and applicable to many cities. The “positive effects” of landscape elements, however, vary with climatic and geographic conditions. One method of evaluating elements such as green roofs, permeable pavement, vegetated walls, rain gardens, and bio- swales considers their contribution to stormwater management. In this study, runoff depth, volume, peak- flow rate, and the mass loading of contaminants, determined through analysis of a typical Calgary residential site using climatic data and simulation tools (NRCS-CN, crop coefficient, and Rational Methods), are compared with those in two green- intervention scenarios with differing landscape elements achieving a Seattle Green Factor of 0.3.


Runoff Reduction Effects

This research focuses on the contribution of green roofs towards reducing stormwater runoff in the cities of Kelowna and Vancouver. The existing stormwater runoff and the potential runoff reduction of green roofs are calculated using local climatic data, such as rainfall, snowfall, evaporation and temperature. Two selected sites are analysed, including both commercial and residential buildings in Kelowna and downtown Vancouver, and are compared to show the particular effects of stormwater management in different climatic zones.