A Hydrological–hydraulic Modeling Framework for 2d Simulation of Street-level Urban Flooding

The reduction of permeable areas due to urban expansion, coupled with inadequate maintenance and the undersizing of drainage systems, has exacerbated urban flooding by increasing surface runoff. This study proposes an integrated framework that combines a VBA-based hydrological model with HEC-RAS 2D simulations supported by a highresolution digital terrain model explicitly representing curbs and gutters. Using a design storm, the model generated lot- and catchment-scale hydrographs and simulated flood dynamics at 1-s resolution. Results indicate that enforcing a ≥20% permeable-area quota in highly impervious lots produced negligible reductions in flood extent and depth. In contrast, strategically placed stormwater inlets, especially upstream and on both sides of streets, substantially reduced water depths and curbed overtopping. The findings demonstrate that permeability policies alone cannot mitigate flooding in consolidated urban fabrics, but that the proposed framework provides a reliable tool to diagnose critical hotspots and evaluate structural interventions.