Selection of substrate amendements improving hydrological properties of extensive green roofs in Japan

Abstract

Stormwater management constitutes a major problem in cities. The increase in impermeable surfaces due to urbanization reduces the absorption of this water and exacerbates the problem. Green roofs are one of the solutions that would lower these volumes of runoff water. Nevertheless, they can act as a source of pollutant. Therefore, this study is conducted to analyze the impact of several substrates on runoff water in order to reduce its volume and optimize its quality. Different mixtures composed of conventional substrate, coco peat and rice husk were tested. While the results showed that different substrates did not have significant impacts on the sum of drainage water collected during the entire period, some collections enable drawing conclusions. In these latter, the RH50 emerged as the most suitable to retain water. Quality analyses highlighted that the conventional substrate was a source of NO3 and absorbed Ca, Mg and Na. The increase in the percentage of coco peat leads to an elevation of the C and Fe concentration while decreasing the Cl concentration. At the same time, the rise in the percentage of rice husk induces a source of SO4, Ba, K and V while it absorbs Ca, Mg and Na.