Investigating the impacts of the regression of Posidonia oceanica on hydrodynamics and sediment transport in Giens Gulf

Posidonia oceanica plays a significant role in the stabilization and protection of the coast in Gulf of Giens. Unfortunately, its distribution has been declining remarkably due to both anthropogenic interventions and natural factors. The present study focuses on the numerical simulation of the presence of Posidonia as well as the influence of its disappearance on hydrodynamics and sediment transport along Alamanarre beach. The model results indicate that the regression of Posidonia leads to significant changes of the hydrodynamic parameters, sedimentation rates, and causes severe erosion along Almanarre beach. In the annual wind conditions, the mean current speed is increased by 50.38%-80.65%, the mean significant wave height increased by 14.03%-16.58%, and the total load of sediment increased by 252%-426%, in absence of Posidonia. Regarding the seasonal wind variation, the disappearance of Posidonia induces an increase of the mean current speed about 52.86%-58.34%, the mean significant wave height by 8.23%-11.27%, and sediment transport rate by 358.99%-394.53%. Under the impact of extreme events with the disappearance of Posidonia, the mean current speed, the mean significant wave height, and the sediment transport rate increase by 12.53%-58.48%, 23.91%-34.67%, and 65.15%-154.62%, respectively.