ABSTRACT Workflow combining ArcHydro preprocessing and HEC-RAS 2D modelling to assess urban flood risk in Tetouan using DEM, hydrological inputs and hazard mapping. Urban flooding represents a significant environmental challenge in northern Morocco, particularly in the city of Tetouan, where recurrent flood events are associated with rapid runoff within the Martil River basin. Accelerated urban expansion into natural floodplains and the obstruction of traditional drainage pathways have increased vulnerability to intense rainfall, while the surrounding steep slopes concentrate runoff towards the low-lying Martil plain, frequently exceeding the capacity of existing drainage infrastructure. This study assesses urban flood risk using a two-dimensional hydraulic modelling approach implemented in HEC-RAS and integrated with ArcHydro for terrain and drainage preprocessing. A 30 m digital elevation model was used to simulate flood propagation under 50- and 100-year return-period scenarios. The modelling results reveal significant spatial variability in flood dynamics, with critical urban zones experiencing water depths approaching 2 m and flow velocities exceeding 2 m/s during extreme events. The analysis highlights the combined influence of topography, urban encroachment and drainage limitations on flood behaviour. The resulting flood hazard indicators (including water depth, velocity and hazard index maps) provide spatially explicit information that can support flood-risk zoning, urban planning strategies and the design of climate-resilient infrastructure in rapidly expanding Mediterranean cities.
Saleh Eddine ZAHLI (Fri,) studied this question.