* Corresponding author: mstone@uwaterloo.ca 26 Treatment Performance of an Extensive Vegetated Roof in Waterloo, Ontario Kyle Vander Linden 1 and Micheal Stone 2 * 1 School of Planning, University of Waterloo, Waterloo, ON N2L 5G1 2 School of Planning and Department of Geography, University of Waterloo, Waterloo, ON N2L 5G1 Vegetated roof technologies are used as treatment measures to mitigate the effects of urban stormwater. A mass balance approach was used to assess the treatment performance of a vegetated roof located on the City Hall in Waterloo, Ontario. The vegetated and control roof sections were instrumented to measure precipitation, storage, and outfow for 18 storm events from June to October, 2006. Concentrations of suspended solids, total phosphorus (TP), and SRP (SRP) in precipitation and roof (vegetated and control) runoff were measured. A total of 155.6 mm of rain fell during the study period. The vegetated roof retained 64.5 mm (43.9%) of the total rainfall while the control roof retained approximately 5.1 mm (4.0%). For individual rain events, the vegetated roof retained an average of 3.5 mm (47.6%), while the control roof retained approximately 0.3 mm (4.7%). Water retention varied with storm size, season, and frequency of storm events. The vegetated roof retained 80.1% of precipitation for storm events ≤3.5 mm, and 34.9% for storm events >3.5 mm. TP and SRP concentrations from the vegetated roof were signifcantly higher than either the precipitation or runoff from the control roof. Key words: green roof, source control, treatment performance, water quality, suspended solids, phosphorus Introduction The effects of stormwater runoff on the health of aquatic ecosystems (Novotony and Olem 1994), fooding (U.S. EPA 1999; Paul and Meyer 2001), and drinking water supplies (Marsalek et al. 2006) are well documented. Accordingly, there is increasing interest globally to implement sustainable urban drainage systems (SUDS) which employ a variety of source, conveyance, and end of pipe controls designed to reduce the volume of stormwater runoff (Marsalek and Chocat 2002; Graham et al. 2004). Vegetated roofs are increasingly being recognized as one source control measure that could be effectively implemented in both new and retroft buildings to reduce runoff volume (TRCA 2006). Much of the innovation in vegetated roof technology, policy, and research (Ngan 2004; GRHC 2005; Cannata 2005; Getter and Rowe 2006) was initially developed in Germany and has subsequently been used to develop regulations in Europe that promote the application of vegetated roofs for stormwater management (Ngan 2004; GRHC 2006). In North America, however, several barriers (fnancial constraints, public awareness, quantifable research, technical expertise, and industry standardization) limit broad application of vegetated roof technology as a viable source control measure (Getter and Rowe 2006). The application and treatment performance of various vegetated roof technologies vary due to a range of climatic conditions which limit broader adoption of the technology (VanWoert et al. 2005). The implementation and effectiveness of vegetated roofs can vary at the city and regional scale and especially between localities that have fnancial incentives for vegetated roof construction, i.e., Toronto, Chicago, and Portland (Peck and Goucher 2005; Getter and Rowe 2006). Consequently, there is a need to assess the treatment performance of vegetated roofs across varying geographical locations, and to develop and implement relevant policies for their use as source control measures. Such information is required to create vegetated roof building and performance standards, and to lower cost by adopting fnancial incentives or stormwater fee rebates that may encourage green roof industry growth. Given the need to increase knowledge of the utility of vegetated roofs as a viable source control measure, the objective of this paper was to evaluate the treatment performance of an extensive vegetated roof located on a municipal building in the City of Waterloo, Ontario. The vegetated roof and a control roof were instrumented to measure precipitation inputs, storage, and runoff during 18 storm events that occurred between June 2 and October 22, 2006. The rates and magnitude of water storage and loss from the vegetated roof and a control roof are reported. Event mean concentrations and temporal variability of suspended solids (SS), total phosphorus (TP) and SRP (SRP) in precipitation and roof runoff are presented. Methods Description of Study Site The vegetated and control roof are located on the Waterloo City Hall building in Waterloo, Ontario Water Qual. Res. J. Can. 2009 · Volume 44, No. 1, 26-32 Copyright © 2009, CAWQ Downloaded from http://iwaponline.com/wqrj/article-pdf/44/1/26/229531/wqrjc0440026.pdf by guest on 20 January 2022