Water retention on the extensive green roof models

One of the main problems of urbanization is the continuous growth of sealed surfaces. Impermeable surfaces i.e. roofs, roads or pavements have dominated land cover, increasing surface runoff and limiting groundwater runoff, often contributing to increased flood risk. The practice of many countries has shown that green roofs are one of the solutions to the problem of rainwaters on the urban areas. The aim of the study was to assess the retention ability of three green roofs of extensive type with different substrate composition (two mineral-organic mixtures, one mineral mixture). The research was carried out at the Water Centre of the Warsaw University of Life Sciences in Warsaw (Ursynów district) in the period from June to November in 2016. The obtained results were compared with observation of the reference model – bituminous roof. Model studies have shown that green roofs retained water in the range from 9.5 mm to 67.1 mm. The average runoff coefficients for green roof types in the period from June to November in 2016 were from 0.31 to 0.33. The obtained results showed slight differences in outflows with different substrates. During high rainfall, the differences in the runoff between the green roofs and the reference roof were negligible.