Simulation of the flood process in urban surface-underground space under extreme rainfall

Urban waterlogging due to extreme precipitation presents an increasingly serious challenge. Pooling of large volumes of surface water can result in flooding of underground spaces. However, there remains limited studies on flooding of underground spaces through the application of hydrological and hydrodynamic models. This study examined flooding in an urban district of Zhengzhou City, China during an extreme rainstorm event on 20th July, 2021. An integrated simulation model of regional surface and underground spaces was established based on InfoWorks Integrated Catchment Model (ICM) software. The generalized reservoir and hydraulic connectivity methods were used to simulate underground spaces. Factors contributing to the initiation and development of flooding of underground spaces were analyzed. The results showed that underground waterlogging was less conducive to alleviation of surface water ponding. The advantages of the generalized reservoir method were shown to be its relative simplicity and feasibility, whereas that of the hydraulic connection method was its detailed representation of underground flooding. Both the cumulative quantity of rainfall and rainfall intensity were shown to have important effects on underground inundation. The results of this study can help to improve urban stormwater forecasting and warning systems, and provide a theoretical basis for regional disaster prevention and reduction.