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Green Roof Stormwater Retention

Effects of Roof Surface, Slope, and Media Depth

^a Department of Horticulture, Michigan State University, East Lansing, MI 48824
^b Department of Geography, Michigan State University, East Lansing, MI 48824
^c Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824
^d College of Agriculture and Natural Resources Statistical Consulting Center, Michigan State University, East Lansing, MI 48824

View larger version (122K): [in a new window]   Fig. 1. Graphic representation of the model-scale roof platforms used to evaluate stormwater retention in the roof surface comparison study.

View larger version (92K): [in a new window]   Fig. 2. Cross-section of a representative extensive green roof system including typically used layers.

View larger version (21K): [in a new window]   Fig. 3. Daily precipitation (mm) during the experimental study (28 Aug. 2002 through 31 Oct. 2003). Values are averages of measurements taken using three tipping bucket rain gauges mounted at the research site.

View larger version (37K): [in a new window]   Fig. 4. Runoff hydrographs of selected representative (A) light (1.27 mm), (B) medium (4.06 mm), and (C) heavy (10.08 mm) rain events recorded at 5-min intervals. Lines represent either rainfall (mm) or runoff (mm) from conventional roofs with a gravel ballast (gravel), nonvegetated green roofs with media only (media), or vegetated green roof treatments (vegetated). Values are averages of measurements taken using three tipping bucket rain gauges.

View larger version (33K): [in a new window]   Fig. 5. Cumulative runoff hydrographs of selected representative (A) light (1.27 mm), (B) medium (4.06 mm), and (C) heavy (10.08 mm) rain events recorded at 5-min intervals. Lines represent either rainfall (mm) or runoff (mm) from conventional roofs with a gravel ballast (gravel), nonvegetated green roofs with media only (media), or vegetated green roof treatments (vegetated). Values are averages of measurements taken using three tipping bucket rain gauges.

View larger version (40K): [in a new window]   Fig. 6. Retention percentage (%) averaged for all measured rain events in respective categories (light, n = 26; medium, n = 30; heavy, n = 27; overall, n = 83) for each roof treatment. Letters above bars represent mean separation among treatments within each rainfall category by Tukey's Studentized Range (HSD) test, P 0.05, n = 3. Error bars represent standard error symmetrical around the mean, but only the positive side is shown on the graph.

View larger version (39K): [in a new window]   Fig. 7. Runoff hydrographs of selected representative (A) light (1.27 mm), (B) medium (4.06 mm), and (C) heavy (10.08 mm) rain events recorded at 5-min intervals. Lines represent either rainfall (mm) or runoff (mm) from vegetated green roof platforms set at a 2% roof slope with 2.5 cm of media (2%–2.5 cm), 2% roof slope with 4 cm of media (2%–4 cm), 6.5% roof slope with 4 cm of media (6.5%–4 cm), or 6.5% roof slope with 6 cm of media (6.5%–6 cm). Values are averages of three replications measured using tipping bucket rain gauges mounted at the research site.

View larger version (43K): [in a new window]   Fig. 8. Cumulative runoff hydrographs of selected representative (A) light (1.27 mm), (B) medium (4.06 mm), and (C) heavy (10.08 mm) rain events recorded at 5-min intervals. Lines represent either rainfall (mm) or runoff (mm) from vegetated green roof platforms set at a 2% roof slope with 2.5 cm of media (2%–2.5 cm), 2% roof slope with 4 cm of media (2%–4 cm), 6.5% roof slope with 4 cm of media (6.5%–4 cm), or 6.5% roof slope with 6 cm of media (6.5%–6 cm). Values are averages of three replications measured using tipping bucket rain gauges mounted at the research site.

View larger version (52K): [in a new window]   Fig. 9. Retention percentage (%) for all measured rain events in respective categories (light, n = 26; medium, n = 30; heavy, n = 27; overall, n = 83) for each roof slope and media depth treatment. Treatments were as follows: 2% roof slope with 2.5 cm of media (2%–2.5 cm), 2% roof slope with 4 cm of media (2%–4 cm), 6.5% roof slope with 4 cm of media (6.5%–4 cm), and 6.5% roof slope with 6 cm of media (6.5%–6 cm). Letters above bars represent mean separation among treatments within each rainfall category by Tukey's Studentized Range (HSD) test, P 0.05, n = 3. Error bars represent standard error symmetrical around the mean, but only the positive side is shown on the graph.