Three-dimensional hydrodynamic modelling of the Moroccan Atlantic coast: A case study of Agadir bay

Coastal areas are a noteworthy source of commercial and economic fortunes for surrounding municipalities throughout the Moroccan Atlantic coast. Thus, a deep knowledge of local hydrodynamics and environmental processes associated is integral to effective coastal management. 3D hydrodynamic model that includes a Lagrangian particle simulation can participate to this understanding of dynamics. The model was calibrated and validated against meteorological conditions, sea surface level, harmonic tidal constituents, water temperature and salinity using a combination of available in-situ measurements, satellite, and ARGO floats data. Subsequently, it was used to determine the pathway of passive tracers and estimate the local residence time (RT). Despite some discrepancies, the findings revealed a good match between simulations and observations, which underlines the feasibility of the model in predicting the main dynamic features of the Agadir bay. Overall, the hydrodynamics of the area is tidal dominated by semidiurnal tides (M2) and governed by westerly and northwesterly winds. Passive tracer simulations showed strong seasonal and spatial variability, conditioning the obtained RTs, with mean values much shorter during summer (3 to 9 days) than winter (5 to 15 days). The tracers look to be trapped inside a coastal cyclonic eddy that increases the RTs in the southern bay, making it an area with highest likelihood of accumulation of pollutants while favoring the northward transport and decrease RTs in the northern bay.