Evaluation of a sediment trap system created in the Oualidia lagoon (Moroccan Atlantic coast) to remedy the silting up of its channel: numerical modeling investigation

The Oualidia lagoon (Morocco) is a RAMSAR site due to its importance as an essential paralic ecosystem for migratory birds. In the late 2000s, this environment suffered from a silting up of its channel which caused a confinement and a total or partial suspension of some ecosystem services. In 2011, after a study of the hydrodynamics of the lagoon, a sediment trap system was created to remedy the silting of the lagoon.

In this study, we investigate the actual hydrodynamic behavior of the lagoon after 10 years of the creation of the sediment trap, using a 2D hydrodynamic model to analyze and monitor the lagoon hydrodynamic. We created a numerical grid using updated bathymetric data that was collected in April 2021 and covers the entire lagoon and a large part of the open ocean. Using this grid, we ran the model over a period of one month, from 1^st to 30^th April 2021, to cover all tidal frequencies, using a time step of 10 minutes. This period was chosen to correspond to the period of in situ measurements (using ADCP equipment) in order to be able to compare the measured and simulated outputs. The hydrodynamic circulation of the lagoon was simulated taking into account different forces such as tides and winds. As a result, the final model outputs are in agreement with the measured data. The simulation with water level and winds produced current values closest to those measured at three different stations inside the lagoon. The comparison of a state of progress from 2011 to 2021 showed a slow but successful role of the sediment trap.