2,124
edits
Changes
Jump to navigation
Jump to search
Line 169:
Line 169: − Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and [[Evapotranspiration| evapotranspiration]] of precipitation. Line 181:
Line 180: + + − + + + + + − The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through evapotranspiration. + − *In Southern Ontario rainwater retention of extensive green roofs without irrigation is between 60% and 70%<ref>Liu, M. Minor, J. 2005. Performance evaluation of an extensive green roof. National Research Council of Canada. NRCC-48204 https://sustainabletechnologies.ca/app/uploads/2013/03/NRC_EastviewGRrept.pdf</ref> <ref name=VS>Van Seters, T., Rocha, L., Smith, D., MacMillan, G. 2009. Evaluation of Green Roofs for Runoff Retention, Runoff Quality, and Leachability, Vol. 44 (1): 33 - 47 (2009). Innovative Approaches to Stormwater Management in Canada</ref> <ref name=Hill>Hill J, Drake J, Sleep B, Margolis L. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. doi:10.1061/(ASCE)HE.1943-5584.0001534</ref>. + − *Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around 50% <ref name=VS/><ref name=Hill/>. − *Using a compost based planting medium improves retention by around 10% i.e. 60 % for compost compared to 50% for granular. − *Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation. i.e. 40% for irrigated compared to 60% without irrigation<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modeled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone. − An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>Curve Number and Runoff Coefficients for Extensive Living Roofs+ − Elizabeth Fassman-Beck, Ph.D., A.M.ASCE; William Hunt, Ph.D., P.E., M.ASCE; Robert Berghage, Ph.D.; Donald Carpenter, Ph.D., P.E., M.ASCE; Timothy Kurtz, P.E., M.ASCE; Virginia Stovin, Ph.D.; and Bridget Wadzuk, Ph.D., A.M.ASCE</ref><ref name=Hill/>. − + − + Line 227:
Line 228: +
→Proprietary systems
[[File:YorkU2.jpg|thumb|Detail showing the early root development through the mat to the granular planting medium.]]
[[File:YorkU2.jpg|thumb|Detail showing the early root development through the mat to the granular planting medium.]]
{| class="wikitable"
{| class="wikitable"
|+ Ability of green roofs to meet SWM objectives
|+ Ability of green roofs to meet SWM objectives
|Partial: Through interception and evapotranspiration
|Partial: Through interception and evapotranspiration
|}
|}
===Water Balance===
Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and [[Evapotranspiration| evapotranspiration]] of precipitation that falls on the roof. The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through [[Evapotranspiration| evapotranspiration]]. Considerable research has been conducted in recent years to define the runoff reduction or water retention capacity of extensive green roofs in climates similar to those that occur in Ontario and Canada.
Controlled studies have indicated that maturing green roofs may have improved water retention properties <ref>Simon De-Ville, Manoj Menon, Xiaodong Jia, George Reed, Virginia Stovin. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance, In Journal of Hydrology, Volume 547, Pages 332-344, ISSN 0022-1694, https://doi.org/10.1016/j.jhydrol.2017.02.006.</ref>.
* Controlled studies have indicated that maturing green roofs may have improved water retention properties <ref>De-Ville, S., Menon, M., Jia, X., Reed, G., Stovin, V. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance. Journal of Hydrology. Volume 547. pp 332-344. https://doi.org/10.1016/j.jhydrol.2017.02.006.</ref>.
* In Southern Ontario rainwater retention of extensive green roofs without irrigation is between 57% and 70%<ref>Liu, M. Minor, J. 2005. Performance evaluation of an extensive green roof. National Research Council of Canada. NRCC-48204 https://sustainabletechnologies.ca/app/uploads/2013/03/NRC_EastviewGRrept.pdf</ref> <ref name=VS>Van Seters, T., Rocha, L., Smith, D., MacMillan, G. 2009. Evaluation of Green Roofs for Runoff Retention, Runoff Quality, and Leachability, Vol. 44 (1): 33 - 47 (2009). Innovative Approaches to Stormwater Management in Canada https://sustainabletechnologies.ca/app/uploads/2013/03/WaterQualResearchJournalCanada_YorkU-Greenroof.pdf</ref> <ref name=Hill>Hill J, Drake J, Sleep B, Margolis L. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. doi:10.1061/(ASCE)HE.1943-5584.0001534</ref>.
* Including winter periods with snow accumulation and thaw, the annual retention of extensive green roofs is around 50% <ref name=VS/><ref name=Hill/>.
* Using a compost based planting medium improves retention by around 10% (i.e., 60% for compost compared to 50% for granular).
* Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.
An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>
Fassman-Beck, E., Hunt, W., P.E. Robert Berghage, R., Donald Carpenter, D., Kurtz, T., Stovin, V., Wadzuk, B. 2016. Curve Number and Runoff Coefficients for Extensive Living Roofs. Journal of Hydrologic Engineering. Vol.21. Issue 3. ASCE. https://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001318</ref> <ref name=Hill/>.
In a study to investigate how green roof runoff reduction performance is affected by climate, Talebi et al. (2019) used water balance and evapotranspiration models to simulate runoff produced by green roofs in six Canadian cities (Vancouver, Calgary, Regina, Toronto, London and Halifax). Results showed that predicted runoff reduction performance varied from 17% to 50% for low water use plants. The best performance was predicted to occur in Regina and Calgary (drier climates), while the poorest performance was predicted for Halifax and Vancouver (wetter climates). Average annual runoff reduction was highest in Toronto and London and lowest in Vancouver.<ref>Talebi, A., Bagg, S., Sleep, B.S., O'Carroll, D.M. 2019. Water retention performance of green roof technology: A comparison of Canadian climates. Ecological Engineering, 126, (2019), 1-15. https://www.sciencedirect.com/science/article/abs/pii/S0925857418303835?via%3Dihub</ref>
===Water quality===
===Water Quality===
Many green roofs receive only rainwater, which is relatively free of contaminants like nutrients and heavy metals, but can contribute contaminants to roof runoff, most notably through leaching of [[Nutrients]] from the growing medium substrate during early establishment.<ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref> Concentrations of Total [[Phosphorus]] in green roof runoff have been observed to vary from 0.4 mg/L to over 10 mg/L.<ref>Hill J., Drake J., Sleep B., Margolis L. 2017. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. doi:10.1061/(ASCE)HE.1943-5584.0001534</ref>. Such concentrations are well above the Ontario Provincial Water Quality Objective of 0.03 mg/L for Total Phosphorus (OMOEE, 1994<ref>Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.</ref>). To improve the quality of runoff from green roofs, Vijayaraghavan et al. (2018) recommend considering the sorption capacity of the growing medium substrate, the phytoremediation potential of plants and incorporation of sorbent [[Additives]] to growing medium substrates.<ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref>
Many green roofs receive only rainwater, which is relatively free of contaminants like nutrients and heavy metals, but can contribute contaminants to roof runoff, most notably through leaching of dissolved [[Nutrients]] and [[Heavy metals]] from the growing medium substrate during early establishment.<ref>Hathaway, A.M., Hunt, W.F., Jennings, G.D. 2008. A field study of green roof hydrologic and water quality performance. Transactions of the ASABE. Vol. 51 (1) pp. 1-8. https://elibrary.asabe.org/abstract.asp?aid=24225</ref> <ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref> Concentrations of Total [[Phosphorus]] in green roof runoff have been observed to vary from 0.4 mg/L to over 10 mg/L.<ref>Hill J., Drake J., Sleep B., Margolis L. 2017. Influences of Four Extensive Green Roof Design Variables on Stormwater Hydrology. J Hydrol Eng. 2017;22(8):04017019. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29HE.1943-5584.0001534</ref>. Such concentrations are well above the Ontario Provincial Water Quality Objective of 0.03 mg/L for Total Phosphorus (OMOEE, 1994<ref>Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.</ref>) to control excessive plant growth in rivers and streams. To improve the quality of runoff from green roofs, Vijayaraghavan et al. (2018) recommend considering the sorption capacity of the growing medium substrate, the phytoremediation potential of plants, and incorporation of sorbent [[Additives]] to growing medium substrates.<ref>Vijayaraghavan, K., Harkishore Kumar Reddy, D., Yun, Y. 2018. Improving the quality of runoff from green roofs through synergistic biosorption and phytoremediation techniques: A review. Sustainable Cities and Society. 46 (2019) 101381. https://www.sciencedirect.com/science/article/abs/pii/S2210670718319383?via%3Dihub</ref>
In dense urban centres, green roofs are increasingly being used to receive irrigation from harvested rainwater. Current Ontario Building Code permits the use of rooftop runoff for landscape irrigation purposes, so long as it is 'free of solids'.
In dense urban centres, green roofs are increasingly being used to receive irrigation from harvested rainwater. Current Ontario Building Code permits the use of rooftop runoff for landscape irrigation purposes, so long as it is 'free of solids'.
*[http://www.vitaroofs.com/ VitaRoofs]
*[http://www.vitaroofs.com/ VitaRoofs]
*[https://www.zinco.ca/ Zinco]
*[https://www.zinco.ca/ Zinco]
*[https://www.soprema.ca/en/sopranature-vegetated-systems/ Soprema]
==Green roofs gallery==
==Green roofs gallery==