Electronic Thesis and Dissertation Repository


Master of Engineering Science


Civil and Environmental Engineering


Denis O'Carroll


Green roofs are gaining recognition in North America as effective tools for managing stormwater runoff in urban areas. A greater understanding of how green roofs perform with respect to fundamental stormwater management criteria, such as stormwater retention and peak flow attenuation is required. This study investigated the impact that changing climates have on the retention performance of three green roofs in London, Calgary, and Halifax. It was found that Calgary (67%) has significantly better retention performance then both London (48%) and Halifax (34%). However, London retained the greatest volume of stormwater (758 mm), followed by Halifax (517 mm) then Calgary (474 mm).

Further monitoring of the hydrologic response for a fourth green roof in London Ontario was conducted to identify and measure the fundamental processes of peak attenuation on a green roof. It was determined that field capacity is a quantifiable point, after which peak attenuation performance significantly decreases. Before field capacity peak attenuation is governed by capillary storage (72%) and routing (7%). After field capacity, gravity storage provides peak attenuation (22%) and drainage routing plays a larger role (11%). A predictive model was developed using Richards equation to simulate the outflow hydrographs of a green roof. Model results show that there is no significant difference from observed data for the performance metrics (ie., water storage, drainage, and peak flow rate).

For the first time in green roof literature the impact of climate on retention was assessed, the processes of peak attenuation were quantified, and an accurate predictive model was presented.