A new approach for urban flood risk assessment using coupled SWMM-HEC-RAS-2D model

Urban stormwater management is crucial for mitigating the impacts of flooding in urban areas, as it plays a vital role in protecting infrastructures, ensuring public safety, and preserving environmental quality. In this study, we develop a new method to quantify urban flood risk (UFR) by integrating the components of hazard magnitude and vulnerability. The hazard is assessed using a coupled SWMM-HEC-RAS 2D model, where the flooding rate calculated by SWMM at each node is automatically fed into HEC-RAS-2D. This integration enables the calculation of the temporal and spatial variations of flood velocity and depth across the urban landscape, allowing for a more accurate representation of flood dynamics. Conversely, vulnerability is evaluated by considering several indicators, including building use, number of floors, construction quality, building age, and materials used in construction. Finally, the UFR as a multi-dimensional factor is calculated by multiplying the standardized hazard and vulnerability components. We successfully examined our proposed method in a part of Karaj City in the north of Iran. According to the findings, although the majority of southern regions of the study area with more deteriorated and aging-drainage-network are experiencing higher hazard magnitudes, the western areas have higher UFR than the others. Our proposed methodology provides a comparative UFR throughout the urban area and can help the managers to take the most effective decisions for flood management. Additionally, the method has the ability to weighting the priorities of hazard and vulnerability components in UFR assessment.