A Hydrological–hydraulic Modeling Framework for 2D Simulations of Street-level Urban Flooding

Abstract The reduction of permeable areas due to from 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 two-dimensional HEC-RAS simulations supported by a high-resolution digital terrain model explicitly representing curbs and gutters. Using a 2 h design storm with a 5- year return period, the model generated lot- and catchment-scale hydrographs and simulated flood dynamics at 1-s resolution. Results showed 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 indicate that permeability-based policies alone are insufficient to mitigate flooding in consolidated urban areas, whereas the proposed framework provides a reliable tool to diagnoses of critical hotspots and evaluations structural interventions.