Effectiveness Analysis of Urban Water Circulation Improvement Facility: A Case Study of Flood-Prone Areas in Sejong City

This study quantitatively analyzed the flood-reduction effects of Water Circulation Improvement Facilities (WIFs) under climate crisis conditions in the Yongpo Drainage Basin, a flood-prone area in Sejong City. As part of the low-impact development strategies, three types of WIFs—Permeable Pavement (PP), Green Roof (GR), and Infiltration Trench (IT)—were selected, and each facility was applied to 5%, 10%, and 15% of the total drainage area, respectively. The rainfall-runoff process was simulated using the EPA SWMM model. For the rainfall input data, both present (1981-2005) and future (2026-2050) precipitation datasets based on the SSP2-4.5 scenario were utilized, and their reliability was enhanced through the application of the Quantile Delta Mapping bias correction method. The results showed that the GR scenario achieved the highest runoff reduction, whereas PP and IT exhibited significant flood mitigation effects only when applied to more than 15% of the watershed area. Inland flooding in the Yongpo drainage basin was mainly attributed to elevated river stages and insufficient storm-sewer conveyance capacity. Theoretical analysis indicates that even when permeable pavement and infiltration trenches are applied to 15% of the total watershed area, they achieve only a 29.5% reduction in increased stormwater runoff. This means that the WIF alone is insufficient to overcome the fundamental limitations of inland drainage. Therefore, this study emphasizes the need for a hybrid water management strategy that combines distributed WIFs with medium- to large-scale detention facilities for effective urban flood control. These findings are expected to contribute to the establishment of an integrated urban water circulation management system that comprehensively considers hydrological, water quality, and landscape aspects during the urban planning stage.