Laboratory Study of Wave Attenuation by Mangrove Forest

Abstract

Coastal vegetation can dissipate the energy of storm surge and tsunami, which serves a natural barrier for coastal protection. The experimental study of waves-mangroves interaction was carried out to evaluate the efficiency of wave attenuation by vegetation (WDV). In particular, the model mangrove consisted of a flexible canopy and a rigid stem to imitate natural Rhizophora better. It considered the effect of various wave conditions including incident wave height (${H_i}$) and wave period ($T$) as well as plant characteristics including submergence ratio ($\alpha $) and stem density ($N$), respectively. Then, the exponential wave decay coefficient (${K_i}$) was applied to determine the performance of WDV. It showed that larger ${H_i}$, $\alpha $ and smaller $T$ induced greater wave decay. To quantify WDV, a new analytical model was proposed considering the change of stem arrangement and wave parameters along the vegetation. Further, the drag coefficient, ${C_D}$ of mangrove forest was analytical calibrated by this model, and made a comparison with the previous model. Based on this model, the relationships between ${C_D}$ and some non-dimensional parameters, e.g. Reynolds number, ${\mathop{\rm Re}\nolimits} $ , Keulegan-Carpenter number, $KC$ and Ursell number, ${U_r}$ were established to evaluate and predict the wave decay. Especially, it showed a better correlation relationship than the previous model, and the predicted results showed a good agreement with the experimental data.