针对2024年8月9日强降雨期间莲花桥积水事件，基于MIKE+平台构建了排水管网与河道耦合模型，对积水过程进行模拟分析，并对排水系统运行特征及积水成因进行了诊断。结果显示：①模型模拟结果较好地重现了积水过程。桥区雨水管网未出现节点溢流，溢流发生在污水干管上的检查井；河道流量与水位与实测数据相吻合，RMSE、RE等指标处于合理范围内。②基于模型核算节点冒溢时段累计来水量为3.11×10⁴ m³，最大溢流水深为0.41 m。③4个排口截流设施最大截流量达到2.41 m³/s，同时河水沿着入河排口e倒灌至截流干管，加剧了污水干线压力，最大倒灌量达到1.80 m³/s，两类因素共同作用导致检查井冒溢。分析表明，上游截流设施高负荷运行与下游河道水位顶托的共同作用造成污水检查井冒溢进而引发了桥区积水，从而解释了降雨强度未超过雨水排水系统设计标准时仍发生积水现象的原因，可为类似城市片区内涝诊断与排水系统优化提供参考。

[Objective] The aim of this study is to clarify the mechanism of waterlogging under heavy rainfall in the Lianhua Bridge area，analyze the operational characteristics of the drainage system and the causes of water accumulation，and develop a hindcast simulation model providing a quantitative basis for addressing drainage issues in the bridge area and other similar sunken bridge areas. [Methods] A coupled drainage network-river model was constructed using the MIKE+ platform，including the combined sewer network，stormwater system，and downstream river channels. The model was validated against measured river discharge and water depth data. Key hydraulic indicators，such as pipe fullness，node overflow，and river water levels，were analyzed. The influence of river backwater and backflow on network operation was assessed by combining river outfall discharges with river water level hydrographs. The formation mechanism of waterlogging was examined using node overflow hydrographs. [Results] （1） Simulated river discharge and water depth matched the measured data，with key evaluation indicators within reasonable ranges. Pipe fullness in the combined sewer system generally exceeded 0.8 during peak rainfall，with some sections under full-pipe or surcharged conditions. （2） No node overflow occurred in the stormwater system； overflow was confined to manholes of the DN1800 combined main pipe. （3） Upstream interception facilities diverted large volumes of rainwater into the combined main pipe，increasing hydraulic load，while rising downstream river levels caused reverse flow at the outfalls. The superposition of these factors triggered manhole overflow. （4） Maximum intercepted discharge of the four outfall interception facilities reached 2.41 m³/s； river backflow through Outfall E reached 1.80 m³/s. （5） Total inflow during node overflow was 3.11×10⁴ m³，with a maximum overflow depth of 0.41 m； 91.37% of inflow came from upstream interception，and 8.63% from river backflow. [Conclusions] This study identifies a coupled hazard mechanism where high-load upstream interception and downstream river backwater jointly trigger manhole surcharge. By quantifying the contribution proportions of these key factors，this research explains the phenomenon where waterlogging occurs even when rainfall intensity remains below the design standards of the stormwater system. The findings reveal that water accumulation is primarily triggered by manhole surcharge on the combined main pipe rather than insufficient capacity of the stormwater system. This study provides a scientific basis for outfall regulation，interception pipe optimization，and drainage retrofitting in similar concave overpasses.