Resumen
The existence of impervious areas is one of the most distinguishing characteristics of urban catchments. They decrease infiltration and increase direct runoff in urban catchments. The recent introduction of green infrastructure in urban catchments for the purpose of sustainable development has contributed to the decrease in directly connected impervious areas (DCIA) by isolating existing impervious areas, and consequently, has also contributed to flood risk mitigation. This study coupled the width function-based instantaneous hydrograph (WFIUH), which is able to handle the spatial distribution of the impervious areas, with the concept of the DCIA to assess the impact of decreasing DCIA on the shape of direct runoff hydrographs. Using several scenarios for typical green infrastructure and the corresponding changes of DCIA for a test catchment in Seoul, South Korea, this study evaluated the effect of green infrastructure on the shape of the resulting direct runoff hydrographs and reducing peak flows. The results showed that the changes in the DCIA immediately affect the shape of the direct runoff hydrograph, and decrease peak flows by up to 12% depending on spatial implementation scenarios in the test catchment. This study demonstrates the importance of the DCIA concept for the evaluation of green infrastructures in urban catchments, enabling quantitative assessment of the spatial distribution of impervious areas, and also changes to the DCIA by various types of green infrastructure. The results of this study also suggest that more effective and well-planned green infrastructures could be introduced in urban environments for the purpose of flood risk management.