Inundation mapping of urban areas in case of severe rainfall events using HEC-RAS

The current study investigates the potential of HEC-RAS (2D) in simulating urban inundation patterns in case of sever rainfall scenarios expected in the Ferrara and Rimini cities in Italy. HEC-RAS is one to most known and used hydraulic model for river application, however, its rainfall module is relatively new and sparsely investigated. Comparison of different mesh sizes (10, 25 and 50m) indicated no significant difference in model performance. However, a significant difference was observed in simulation time. Inundation maps were obtained for 5, 20 and 100-year rainfall events. HEC-RAS model outputs are compared against ground evidence and detailed outputs obtained with other modelling scheme: filling-and-spilling algorithm and a two-dimensional (2D) hydraulic numerical model (jn Rimini). For both Ferrara and Rimini case studies, overall index of agreement between HEC-RAS and filling-and-spilling models is up to 88%, while the similarity (i.e., flood area index) between HEC-RAS and 2D hydraulic model simulation at Rimini is equal to 0.64. In general, this study provides addition insights concerning HEC-RAS potential and limitations for identifying pluvial flood-hazard spots across large urban environments.