Mitigation Effects of Integrated Green-Grey-Blue-Control Systems on Urban Flooding in Plain Regions

Urban flooding poses a significant challenge in highly urbanized areas, necessitating effective solutions to enhance sustainable urban stormwater management. This study proposes an Integrated Green-Gray-Blue-Control (IGGBC) system as a comprehensive strategy for urban flood risk mitigation. Through systematic scenario analysis, twelve distinct strategies were examined, including individual green, blue, and gray measures; combined green–blue, green-gray, blue-gray, and gray-green–blue (IGGB) approaches; and five integrated gray-green–blue-control (IGGBC3.2, IGGBC3.0, IGGBC2.8, IGGBC2.6, IGGBC2.4) systems. A 1D- 2D coupled hydrological-hydrodynamic model was employed to simulate urban flood inundation and evaluate the performance of various mitigation strategies. The results indicate that individual measures yielded limited improvements in mitigating urban flooding, as reflected in poor effectiveness index (EI) values. Among combined measures, the green–blue and green-gray combinations demonstrated negligible effectiveness, and the blue-gray combination slightly mitigated urban flooding but still showed insufficient EI values. Additionally, the IGGB measure provided moderate mitigation with a reasonable EI value. In contrast, the IGGBC3.2 measure significantly outperformed IGGB, increasing the inundation reduction ratio from 38.49% to 53.16% and enhancing the EI from 0.52 (good) to 1.00 (excellent), demonstrating its control measures’ effectiveness in alleviating mutual constraints between stormwater drainage systems and flood discharge channels. Notably, the IGGBC system also demonstrated excellent performance in mitigating flood inundation during high-return-period rainfall events. However, a diminishing marginal effect was observed among the different integrated IGGBC systems (IGGBC3.2, IGGBC3.0, IGGBC2.8, IGGBC2.6, IGGBC2.4). This study provides valuable insights for developing effective urban flood management strategies and makes a significant contribution to enhancing urban resilience.