Impacts of rainstorm characteristics on flood inundation mitigation performance of LID measures throughout an urban catchment

The hydrological benefits of sponge city construction have sparked a variety of academic studies and discussions. However, the effectiveness of sponge city construction in mitigating flood inundation at the urban catchment scale remains rarely investigated. Therefore, the Jiaodong catchment in Zhenjiang City, which is a national sponge pilot city and has extensively implemented various LID measures, was selected as a study site. The SWMM-2DCA model was established and validated using measured rainfall and drainage pipe flow processes, as well as historical inundation-prone location records, and then applied to evaluate the accumulative effectiveness of LID measures in flood mitigation under different 2-hour design rainstorms with changing return periods (2, 5, 10, 20, and 30 years) and peak position coefficients (0.2, 0.5, and 0.8). The results revealed that nearly 90% of the inundated area had an inundation depth of less than 0.15 m, and the impact of rainstorm characteristics on the maximum inundation depth was very limited. Both the maximum inundation volume and area were positively related to the return period and the peak position coefficient of rainstorms. The increase in the rainstorm return period could advance the start of inundation and retard the occurrence of peak inundation. The maximum inundation volume and area could be significantly reduced by 63 ∼ 98% and 41 ∼ 96% respectively after the implementation of LID measures, but the average reduction rate for maximum inundation depth was only 3.7% for rainstorms with a return period longer than 10 years. This indicates that LID controls inundation better for volume and area than for depth. The changing patterns of absolute and relative reductions in maximum inundation volume and area with rainstorm characteristics exhibited reverse trends, while the absolute and relative reductions of maximum inundation depth demonstrated similar variations. The absolute reductions in both maximum inundation area and depth almost reached their extreme values at the 10-year rainstorm return period. The effects of LID on the timing of peak inundation depended largely on the peak position of rainstorms. These findings could contribute to a better understanding of the flood inundation mitigation performance of sponge city construction.