Research on the Influence of Underground Space on Urban Waterlogging in Extreme Rainfall

Extreme rainfall could induce urban waterlogging, threatening the life and property on the urban surface and underground space. However, the current hydrodynamic models involve less about underground spaces, and there remain limited studies on the response of urban waterlogging spatial-temporal features to underground defense height. This study reconducted the flooding in the main urban area of Erqi District of Zhengzhou City during the "7·20" extreme rainstorm event, proposing a model considering the flooding of underground space. Under different protective heights of underground spaces, the flood spread on the urban surface is simulated. The results show that:(1)The model, proposed in this study, has a physical mechanism, quantifiable parameters, simple calculation, and is suitable for large-scale simulation. (2)The risk level of the urban surface will be overestimated without considering the flooding of underground spaces. The sum of high-risk and super senior-risk areas will increase by 10.7%. (3)When the defense height of underground space increases by 10cm, the maximum water depth on the urban surface increases by 10.0%, the velocity increases by 2.3%, and the sum of high-risk and super senior-risk areas increases by 3.4%. This result explores the mechanism of the impact of underground space defense height on urban waterlogging providing novel perspectives on setting fortification heights and preventing the overall risk of urban surface underground waterlogging.