Modelisation de la dissipation de l'energie des vagues par la vegetation de marais littoral

Saltmarshes are ecosystems composed of halophyte plants, which influence significantly the sedimentary dynamic. Saltmarshes are modulated by local wave hydrodynamics. As waves progress in the marsh, they erode sediment. However, vegetation dissipates the wave energy and minimises erosion. Therefore, it is important to learn more about the interaction between vegetation and wave hydrodynamics. The purpose of this study was to build a numerical model to simulate the wave propagation through a vegetated intertidal zone. The existing SWAN model (Simulating WAves Nearshore) was used as base model, and a new routine was added to calculate the wave energy dissipation by the vegetation. This routine calculates the drag force caused by the movement of water in the vegetation over the entire canopy height. These calculations are repeated for each wave frequency and for each wave propagation direction.;Field measurements were recorded at the Isle-Verte marsh to calibrate the parameters of the new routine. When dissipation by the vegetation was ignored, the waves height generated by the SWAN model was generally three times higher than the actual measurements at the most landward station in the saltmarsh. When the new routine was added to the model, simulated wave heights were only 6% higher than the measured heights. The results showed a wave energy dissipation of 37% to 88%, and this dissipation was primarily due to wave attenuation by the vegetation over 566 metres. Several simulations of the SWAN model with the new routine were made to determine the influence of different parameters on the dissipation, such as water level, vegetation density and wave period. These model results confirmed preliminaries mathematics analyses. These results will be useful in future studies to better simulate the hydrodynamics in saltmarshes and to understand the sedimentary dynamic in these environments.