Numerical investigation of coastal profile evolution under effect of submerged flexible vegetation by XBeach wave model

•A semi-empirical formula for the flexible vegetation CD is used in the XBeach model.•Wave flume experiments were used to validate the numerical model.•As wave height or period increases, evolution range shows more offshore and wider.•Evolution shows higher quantities with increasing wave height or period.•Longer periods and larger wave heights have more significant effects on evolution. Vegetation communities distributed in coastal zones and offshore wetlands are important compositions for sand stabilization and stability of the ecosystem. This paper studies the impact of flexible vegetation on beach profile evolution by constructing an XBeach numerical model. Firstly, the mathematical model of flexible vegetation beach is established based on the generalized vegetation parameters. The XBeach numerical model is validated by the wave flume experiment to prove that a semi-empirical equation of flexible vegetation drag coefficient is valid in beach profile evolution. Then, the numerical model is used to study the beach profile evolution with flexible vegetation under different wave parameters and summarize the corresponding laws. Finally, the differences between flexible and rigid vegetation on beach evolution are compared. Results show that the beach profile evolution roughly increased with the increase of wave parameters. The Starting Point of Evolution in beach shifts offshore and the evolution range gradually broadens as the wave height or period increases. In addition, the flexible vegetation beach shows greater evolution than rigid vegetation beach and the Starting Point of Evolution also tends to be more offshore, particularly under conditions of long periods and large wave heights. This study can provide references for beach protection and ecological restoration in coastal areas.