Numerical modeling of hydrodynamic and water quality impacts of wastewater discharges in coastal Lagoons: A case study of Ria Formosa

This study investigates the effect of wastewater treatment plant (WWTP) outlet locations on water quality in Ria Formosa lagoon, Portugal. Circulation occurs through six tidal inlets exchanging water with the Atlantic Ocean. A high-resolution 2D hydrodynamic model simulates the lagoon’s circulation and assesses the impact of WWTP. The model is calibrated and validated using field data, achieving RMSE of 0.2 m for water depths using manning value of 0.018 s/m 1/3 . Results identify three hydraulically distinct regions, enabling a smaller domain. A 3D model comparison validates the depth-averaged assumption, confirming the accuracy of the 2D simulations. The 2D model simulates lagoon flushing, showing 90 % tracer reduction within two weeks and 50 % within one week, and examines WWTP discharges, revealing high circulation in most areas, but low-tide challenges in one outlet due to shallow bathymetry. Future work focuses on coupling near-shore and far-shore models with higher-resolution bathymetry to optimize WWTP configurations.