The effect of the substrate depth on hydrological performance of a vegetation roof: Laboratory study

There are increasing demands in cities to reduce the amount of impermeable areas and mitigate water runoff from extreme rainfall.Vegetated roofs are a promising nature-based solution for stormwater management in urban areas.In this study, the retention of rainwater on a roof substrate with different depths and during different rainfall intensities was evaluated.An experiment was conducted in laboratory conditions using a small rainfall simulator.A commercial roof substrate was tested, where by 3 different depths of a substrate were chosen (7, 10, and 14 cm) then, a 15-minute rainfall with 3 intensities (1.3; 2.7, and 3.8 mm min -1 ) was applied.The study revealed variations in higher rainfall intensities of 2.7 mm and 3.8 mm min -1 .A comparison was made using substrate with a depth of 7-10 cm, indicating an 8-16% increase in water retention capacity.The roof substrate with a depth of 10-14 cm increased its retention capacity by 12%.The water retention results can be considered as the maximum limit of possible retention for a 15-minute duration of rainfall at specific 3 intensities.This experiment showed that a longer duration of rain is needed to determine the peak discharge attenuation rate.