Numerical simulations of wave propagation over a vegetated platform

• Quantify the contributions of platform and vegetation to wave height reduction by a vegetated platform using a CFD model.
• Vegetation stems on a vegetated surface breakwater tend to reduce more wave energy than do the roots with the same height.
• Vegetation may increase wave transmission when the platform width is in the range of 37.5–62.5% of the incident wavelength.
• An empirical formula has been developed for predicting the wave transmission over a vegetated free-surface breakwater.

Vegetated platforms have been constructed in recent years for the purpose of shore protection. This paper addresses some fundamental questions concerning the vegetated platform: (1) What is the difference in wave attenuation between a vegetated platform and a simple platform, and how much can vegetation increase the efficiency of reducing wave transmission? (2) Are there any differences between the effects of stems and roots on wave attenuation? (3) Does vegetation always reduce wave transmission? (4) Is it possible to develop an empirical formula for estimating the wave transmission of a vegetated platform? To answer the above questions, a numerical model solving the Navier–Stokes equations for wave propagation over a vegetated platform is established and validated by several existing laboratory experiments. A total of 244 numerical experiments based on this model have been carried out. The simulated results suggest that the platform plays a major role and the vegetation plays a supporting role in reducing wave transmission except for some special cases. Stems tend to have a larger influence than roots in reducing wave transmission with the same height. The roots always help reduce wave transmission, while the stems may increase wave transmission when the platform width is in the range of 37.5–62.5% of the incident wavelength. Based on our numerical experiments and existing laboratory data, the paper proposes a simple formula for predicting the wave transmission coefficient of a vegetated platform for engineering applications.