Effects of slopes on the stormwater attenuation performance in extensive green roof

This study is aimed to determine the effects of slope on stormwater retention and peak flow attenuation performances in extensive green roof in Malaysia. One green roof test bed with dimensions of 2.0 m (length) x 1 m (width) x 0.2 m (height) was constructed in Universiti Tenaga Nasional. The substrate layer was fixed as 130 mm depth and placed on top of the filter fabric and drainage layers. The green roof test bed was planted with Portulaca Grandiflora (sedum species) as the native plant in Malaysia. Different slopes (0 °, 2 °, 5 ° and 7 °) of green roof test bed were tested in this study for its stormwater retention and peak flow attenuation performances. The results show that stormwater retention percentages are ranged from 56.9% to 52.3%. The stormwater retention percentages are decreased as slope increased in this study. Flat slope showed the longest observed time of peak flow while the 7 ° slope has the shortest observed time of peak flow. This finding suggests that slope has a significant impact to the stormwater retention and peak flow attenuation performances in extensive green roof.