The effects of different materials of green roofing on the quantity and quality of stored and drainage water by using simulated rainfall setup

One of the methods to control the rain on the spot and reuse it is the green roof. This method uses a multi-layer system of vegetation on the roof and balcony of a building to absorb part of the rainwater; the volume and peak runoff are also reduced by evaporation, transpiration, and treatment processes. This research was conducted as a field experiment in the hydraulic laboratory of the Agriculture Faculty in the University of Zanjan, Iran. The factors of the study design included a green roof covered with shards of brick and cultivated soil (grass). The experiments were performed at rainfall intensities of 45, 55, and 65 mm/h with 5, 10, and 25 year return periods, respectively. Also, the volume of the water stored and drainage was measured in different conditions. The results of this study showed that regardless of the type of materials used in the green roof, with increasing time, the amount of water stored in the green roof decreased, and the amount of drained water increased. A comparison of the average performance of the brick and grass modifiers for green roofs showed that the volume of the stored water in the grass corrector was higher; if the shards of bricks were used, 69% of the rainfall would be stored, and 31% was drained. However, adding grass to the green roof increased the volume of stored water to 78% and reduced the volume of drainage water to 22%. Also, the presence of grass on the green roof reduced the electrical conductivity by 32% compared to the single brick.