Investigation of the effect of green roof on rainwater drainage system in urban areas

Contemporary cities face major water-related problems, made worse by people moving from rural areas to cities. As more people crowd into urban areas, more buildings and roads are needed. These hard surfaces, like concrete and asphalt, stop rainwater from soaking into the ground naturally. This disrupts the natural water cycle, increasing the risk of floods. Flooding can cause serious harm, including deaths and widespread damage to property. To address these critical issues, a comprehensive rainwater management model was developed for the Bağcılar district of Istanbul. Considering all the information, a total of 487 water collection basins (sub-basins) were created. This model was constructed using the EPA-SWMM (Environmental Protection Agency - Storm Water Management Model), an internationally recognized software for urban stormwater analysis. The model used carefully collected data, including precipitation records from the Florya station, provided by the General Directorate of Meteorology, and detailed infrastructure specifications from the General Directorate of İSKİ (Istanbul Water and Sewerage Administration). This study integrated green roof data into the EPA-SWMM model to evaluate their effectiveness as a Low Impact Development (LID) strategy. The main goal was to determine how well green roofs reduce surface runoff in urban areas and improve rainwater management. The study specifically focused on green roofs as a representative LID application. To thoroughly evaluate their impact, 36 distinct scenarios were formulated. These scenarios systematically varied two key parameters: precipitation return intervals (2, 5, 10, 25, 50, and 100 years) and the percentage of green roof coverage (20%, 40%, 60%, 80%, and 100%). This comprehensive approach allowed for a deep investigation into how green roofs would perform under diverse rainfall magnitudes and frequencies. The model enabled the interpretation of peak water flow at the study area's outlet points, directly correlating these values with various rainfall events. A particularly significant finding emerged from scenarios incorporating a two-year return interval rainfall event and an 80% green roof LID application. In these conditions, a remarkable 85.57% reduction in the total flow rate at the outlet point was observed. but when we apply 50-year series and 60% Green Roof DEK application; the most minimum speed of maximum flow of the outlet point was observed, a decrease of 94.24% occurred. The study conclusively establishes the substantial role of green infrastructure, specifically green roofs, in controlling, managing and reducing stormwater runoff in urban environments.