Numerical simulation-based study on the response of urban drainage networks to flooding and road risk in typical...

In recent years, the increasing frequency of heavy rainfall events has intensified urban pluvial-flood risks, particularly in low-lying, infrastructure-deficient small and medium-sized cities. However, the spatiotemporal mitigation effects of drainage systems-especially within critical urban functional areas such as road networks-remain insufficiently explored. This study develops an integrated hydrodynamic framework combining the two-dimensional GAST model and the one-dimensional SWMM model to simulate 18 rainfall scenarios (return periods of 1a-100a) in Taocheng District, Hengshui, China. Two hydraulic conditions were assessed: with drainage (WN) and without drainage (NN), enabling a comparative analysis of surface inundation regulation, road inundation reduction, and flood-risk redistribution. Results show that under the WN scenario, the drainage system reduced peak surface and road inundation volumes by up to 50.92% and 69.81%, respectively, while advancing the road peak-inundation time by 24-36 min. This temporal decoupling from peak rainfall intensity lowers the likelihood of flow synchronization. In terms of road-flood risk, Level 4 (high-risk) grids decreased by over 65% during the 100a event, with reductions also observed across Levels 1-3-particularly at intersections, low-lying areas, and inlet-dense zones. These findings highlight the critical mitigation role of urban drainage systems during both moderate and extreme rainfall. They underscore the necessity of incorporating drainage infrastructure into urban flood models and risk assessments, supporting the development of climate-adaptive drainage strategies and resilient stormwater management for vulnerable cities.