On the effects of flood reduction for green and grey sponge city measures and their synergistic relationship—Case study in Jinan sponge city pilot area

Abstract

Flooding is a globally common natural hazard that poses increasingly adverse effects to humankinds and society with the increased impact of climate change and rapid urbanization during the past decades, especially those in developing countries. New concepts for stormwater management, such as LID (low impact developments) and BMPs (best management practices), and the SCP (Sponge City Program) of China become important means to reduce flooding disasters. Specifically, the SCP has gained much attention from scholars and engineers worldwide, and has come into practice across China. How the SCP measures work is a realistic issue, and the relationship between green and grey SCP measures remains to be understood. Therefore, in this study, simulations of the flood response under different sponge measure combinations and rainfall scenarios were carried out, and the synergistic effect of different sponge city measures was determined. The results show that the current LID measures in the study area can effectively control light and high-frequency rainfall but show limited effects with respect to extreme and low-frequency rainfall. The combination of LID measures and drainage system upgrading has a better control effect and should be properly employed to avoid harming the downstream area. Both measures fail when confronting extreme rainfall events, and emergency measures are indispensable. The two measures cooperate better to address rainfall with long recurrence intervals and great peak ratios, and show different effects on the alleviation of different flood indicators, which indicates SCP planning according to local conditions. A global angle should be adopted, and localized SCP measures are preferred. This pattern is advisable for cities facing flood problems.