Comparison of Green Roof Performance in Stormwater Mitigation

Ting Fong May Chui, Albert Chun Wai Wong

Monday 29 june 2015

14:50 - 15:05h at North America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Adaptation measures

Parallel session: 2I. Floodrisk - Adaptation

The impervious surfaces in urban areas often increase overland flow and river discharge leading to flooding issues. Green roof, being one low impact development technique, can potentially facilitate stormwater management and advert flooding problems. Although there are a number of studies examining the hydrologic behaviour of green roof, they are often limited to the monitoring periods which may not involve extreme rainfall events. They are also specific to the rainfall conditions of the study areas, making it difficult to transfer the knowledge to other countries. This study uses numerical models to quantify the hydrological behaviour of green roof and to examine the effectiveness of green roof in stormwater management. In particularly, it compares its performance in extreme rainfall events of different countries. A one-dimensional variably-saturated flow model is used. The calibrated model is subjected to the rainfall conditions of a few cities (i.e., Hong Kong, Singapore, Nagoya and London) of two-year return period. The reduction and the delay of the peak discharge, and the fraction of water retained are compared. The green roof performances (e.g., peak reduction, rainfall retained) vary due to the differences in rainfall characteristics (e.g., temporal pattern, total rainfall volume). The modeling results from different countries allow a consistent comparison, generating insights that might facilitate the transfer of results across countries. Overall, this study improves our understanding of hydrological behaviour of green roofs for stormwater management, in particularly benefiting the interpretation of green roof hydrological studies performed at rainfall conditions different from the area of interests.