Hydrodynamics and Water Wenewal in Nador Lagoon (Morocco)

Nador Lagoon, a semi-enclosed basin in northeast Morocco, has recently experienced significant anthropogenic changes, including the creation of a new, wider, and deeper inlet with extended lateral jetties. This lagoon is a vital transitional zone on the North African coast, playing a crucial role both economically and environmentally. Located on Morocco's Mediterranean coast between Cape Three Forks and Cape de l'Eau, it has been the subject of limited research regarding its physical processes. This work is structured around two main objectives: first, to evaluate the performance of the hydrodynamic model using in situ data, and second, to use the model to understand the lagoon’s hydrodynamic processes. Specifically, the study aims to assess the impact of wind and tide on hydrodynamics and water renewal in the Nador Lagoon, which was simulated using a three-dimensional hydrodynamic model. Water renewal was calculated through a passive tracer released inside the lagoon with an initial concentration of 1, allowing the investigation of the lagoon’s renewal capacity under tidal and wind forcing. The results of the hydrodynamic model performance evaluation, based on data from four measurement stations, were presented. The comparison between simulated tides and measured data shows good agreement, with the square of the correlation coefficient (R²) values ranging from 0.97 to 0.99 and Root Mean Square Error (RMSE) values between 0.005 and 0.01m. At a station near the inlet, tidal currents observed at different depths also exhibit a strong correspondence with the simulations (R²=0.92-0.99; RMSE=0.05-0.11m/s). Furthermore, the validation of sea surface temperature Sea Surface Temperature (SST) confirms the model’s ability to reproduce seasonal variability, with R² ≥0.94 and RMSE ≤0.94°C. A distinct monthly variation in currents from January to December has been observed, particularly in shallow coastal areas, which are mainly characterized by southeasterly and northwesterly currents. These circulation patterns have an important influence on the lagoon’s water renewal dynamics. The shortest water renewal time occurs under the influence of west winds, with values ranging from 6 to 16 days from the center to the extremities, and from 6 to 26 days under the influence of east winds. Additionally, during northeasterly winds, the water renewal time can reach up to 60 days, particularly in the southeastern part of the lagoon. In contrast, the extremities of the lagoon experience significantly reduce renewal throughout the year, with times ranging between 6 and 31 days.