Multi-criteria decision analysis and hydrodynamic modeling for flood-safe urban planning: case study of Oued Merzeg, Casablanca (NW Morocco)

Proactive flood hazard mapping and identification is a crucial preliminary step to economic and urban development, as it plays a key role in sustainable development by improving risk management and supporting the design of appropriate solutions to prevent potentially significant damages. This study aims to map flood hazard in the flood-prone area of Oued Merzeg, Morocco, using two approaches: The Analytical Hierarchy Process (AHP) and hydrodynamic modeling. Nine key factors, i.e., elevation, slope, drainage density, Stream Power Index, Topographic Wetness Index, Land Use Land Cover, Normalized Difference Vegetation Index, distance from the river, and rainfall, were selected for AHP-related multi-criteria evaluation. AHP was used to factor weighting and producing a flood susceptibility map, while the hydrodynamic model simulated flood hazard for a 100-year return period event at three different mesh sizes with resolutions of 4m, 8m, and 12m. Validation using observed flood points from January 2021 shows that the AHP map captured a higher proportion of flooded locations (significant: 56.38%; extreme: 0.49%), whereas the hydrodynamic model identified fewer points due to event-specific constraints (significant: 0.25%; extreme: 0.36%). Moreover, the results indicate a high flood hazard in a the populated near coastal area. Incorporating these results into the proposed development plan, this study identifies high-hazard zones that require immediate attention. Some residential and industrial areas, currently outside designated protected zones, are highly susceptible to inundation. Additionally, recommendations and future prospects on flood reduction in the study area are discussed.