Green roof as a potential Sustainable structure for runoff reduction

Urbanisation has changed the vegetated pervious areas into impervious urban roof areas and increase water production and urban heat island effects. In attempt to solve excessive water problems in urban area, green roof or vegetated roof structure as a part of Sustainable Urban Drainage System (SUDS) structure; has been introduced to replicate the pervious vegetated area on vacant urban roofs with role to control water quantity at source. This study examined the potential of green roof at retaining rainfall with less storage available than its maximum water capacity based on the antecedent dry weather period (ADWP) of less than 24 hours. The soil composition has permeability of 0.00011 cm/s with porosity of 55.1% that is equivalent to 44.1 mm available maximum storage from its total substrate depth of 80 mm. Result shows that events with ADWP more than 19 hours were 100% retained while events with ADWP less than 15 hours has shown various retention from 50-100% retention depends on total rainfall. Therefore this study has shown that one of the main factors that affected the retention percentage was the available storage within the green roof itself due to loss activities during dry days.