The Effects of Substrate Types on Rainwater Control on a Container Green Roof

Green roofs have been recognized as a valuable approach to adjust for urban microclimate, purifying rainwater and increasing biodiversity in urban spaces. Besides, it can be used to control rainwater runoff effectively. The adsorption function of green roofs on rainwater runoff mainly depends on the interception effect of the vegetation layer and the absorption and storage effect of the substrate layer. The effects of rainwater runoff are impacted by varying substrate types. In this study, the formation time of runoff for silicate mixed matrix (grass soil: pumice = 3:1) and high-temperature combustion oxide mixed matrix (grass soil: slag = 3:1) were measured and compared in a rainfall simulation experiment. The different responses between their runoff intensity and time were analyzed. The results showed that the runoff formation time was 255 min for the silicate mixed matrix and the runoff peak time was 310 min when the rainfall intensity was 0.3 mm/min and the substrate thickness was 300 mm. The runoff formation time was 230 min for the high temperature combustion oxide mixed matrix and the runoff peak time was 290 min in the same conditions. Both the runoff formation time (over 9.8%) and the peak runoff time (over 6.5%) for the silicate mixed matrix were longer than the time for the high temperature combustion oxide mixed matrix. Based on the results from this study, the silicate mixed matrix is more effective than the high temperature combustion oxide mixed matrix in control rainwater runoff on green roofs.