Simulation of the Impact of Blue-Green Infrastructure Implementation on Surface Runoff Using the Storm Water Management Model in the University of North Sumatera

Abstract

Land use changes in urban areas have increased impervious surfaces, resulting in higher surface runoff and greater pressure on drainage systems. As an educational area dominated by buildings, roads, and parking facilities, the Universitas Sumatera Utara (USU) campus has the potential to generate significant runoff that may contribute to urban flooding. This study evaluates the effects of Green Roof, Permeable Pavement, and their combination on surface runoff in the Outlet 2 drainage catchment using the EPA Storm Water Management Model (SWMM). Rainfall data were obtained from the BBMKG Region I Medan, Tanjung Selamat, and Tuntungan stations. Hydrological analyses included frequency analysis, the Chi-Square goodness-of-fit test, the Mononobe method, and the Alternating Block Method (ABM). Four simulation scenarios were evaluated for 2-year and 5-year return periods: existing conditions, Green Roof, Permeable Pavement, and their combination. Under existing conditions, total surface runoff reached 18.570 × 10⁶ L and 21.360 × 10⁶ L, with average outfall flows of 1.142 m³/s and 1.208 m³/s for the 2-year and 5-year return periods, respectively. The combined implementation produced the greatest runoff reduction, decreasing total surface runoff by 28.76% and 25.00%, while Green Roof was more effective in reducing average outfall flow and Permeable Pavement achieved greater reductions in runoff and flooding volumes. These findings demonstrate that combining both BGI practices provides the most effective strategy for improving urban drainage performance.