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Abstract
Green roofs provide an opportunity to mitigate the negative impact of stormwater runoff. However, scientific research quantifying these character-istics is limited, particularly in the United States. Therefore, our bjective was to quantify the differences in water retention among combinations of various green roof slopes, substrate (media) depths, and vegetation types. Fifteen simulated rooftop platforms measuring 2.4 m x 2.4 m (8 ft x 8 ft) were utilized each containing substrate and a Xeroflor drainage system. Vegetation was a mixture of seven species and cultivars of Sedum. The first study compared slope (2% and 6.5%) and substrate depth (2.5, 4.0, and 6.0 cm), while the second compared vegetation types (Sedum, substrate only, and gravel). The quantity of rainfall retained in the slope/depth study ranged from 74% (2% slope, 4 cm substrate) to 69% (6.5% slope, 4 cm substrate). The effect of vegetation was significantly greater as platforms containing 100% sedum cover retained 66% of the rainfall compared to 63% for substrate without plants and only 25% for a typical commercial roof with gravel ballast. Results indicate that roof slope, substrate depth, and the presence of vegetation all influence retention. One must also consider the intensity and duration of the rainfall as well as substrate moisture content immediately prior to the rainfall event.
Green roofs provide an opportunity to mitigate the negative impact of stormwater runoff. However, scientific research quantifying these character-istics is limited, particularly in the United States. Therefore, our bjective was to quantify the differences in water retention among combinations of various green roof slopes, substrate (media) depths, and vegetation types. Fifteen simulated rooftop platforms measuring 2.4 m x 2.4 m (8 ft x 8 ft) were utilized each containing substrate and a Xeroflor drainage system. Vegetation was a mixture of seven species and cultivars of Sedum. The first study compared slope (2% and 6.5%) and substrate depth (2.5, 4.0, and 6.0 cm), while the second compared vegetation types (Sedum, substrate only, and gravel). The quantity of rainfall retained in the slope/depth study ranged from 74% (2% slope, 4 cm substrate) to 69% (6.5% slope, 4 cm substrate). The effect of vegetation was significantly greater as platforms containing 100% sedum cover retained 66% of the rainfall compared to 63% for substrate without plants and only 25% for a typical commercial roof with gravel ballast. Results indicate that roof slope, substrate depth, and the presence of vegetation all influence retention. One must also consider the intensity and duration of the rainfall as well as substrate moisture content immediately prior to the rainfall event.
Date
5/2003
5/2003
Author(s)
D Rowe, C Rugh, N VanWoert, M Monterusso, D Russell
D Rowe, C Rugh, N VanWoert, M Monterusso, D Russell
Page(s)
Keyword(s)
green roof; runoff; slope; vegetation
green roof; runoff; slope; vegetation