The hydrological performance of a green roof in Sydney, Australia: A tale of two towers

This study describes the sister buildings Daramu house and International house in Barangaroo, Sydney (Australia's largest metropolitan city), with and without a green roof, respectively. Trace metal samples were collected from both roofs and analysed using ICP-MS to determine the bioretention potential of the green roof to remediate soluble and particulate stormwater trace metal contamination. Retention of ambient trace metal contamination by the green roof substrate was deemed significant for soluble copper and particulate zinc, chromium and copper. In addition, hydrological models (DRAINS and SWMM) were applied to predict the performance of the green roof to identify its ability to manage stormwater runoff and frequency, as well as to analyse the green roof's performance in complex surface flooding situations where storage or backwater effects occur in overflow routes and surface flows. Our results demonstrate a reduction in peak stormwater flow by 18.29 L/s (∼50%) for storms as infrequent as 1 in 5 years, and peak flow reductions up to 90% storms of lower intensities. These results are significant as it demonstrates that a green roof could remediating trace metals contamination, thus reducing the impact on aquatic environments through stormwater runoff. It also highlights their potential to reduce stormwater flow, and utilise this additional water for evapotranspiration, leading to cooler ambient temperatures. Future works should aim to quantify the remediation effect of various planted species on in-situ green roofs, as well as determine the specific retention capabilities of various substrate compositions