Stormwater Characteristics of Greenroof Trays and Bags

The research sought to determine the performance of green-roof bags and trays to reduce storm-water peak discharge. In addition, the green roof equipment’s ability to lag the peak discharge and drainage times were also assessed. A laboratory simulation of Johannesburg’s rainfall pattern, of short and intense storms, was conducted on a model scale roof. Results show that the green-roof installation of plants, soil, hessian jute bags, and geo-membrane performed the best in the most intense rainfall conditions by reducing the peak discharge by up to 44%. The hessian jute bags also consistently increased the peak lag time and drainage time. The plastic modular trays were ineffective in reducing discharge at high rainfall intensities. In fact the trays increased the rate of runoff of water from a roof due to the narrow flow channels formed by the tray’s geometry. The research proved that green roofs can be effective water retention and management devices and showed, unexpectedly, that green-roofs can be used to quickly channel water away from roofs. Therefore the research gave comprehensive and measurable information on the behavior of Storm water on green roofs using bags and trays.