Laboratory Study of Wave Attenuation by Mangrove Forest

TL;DR

This study experimentally and analytically investigates how mangrove forests attenuate waves, considering various wave and plant parameters, and introduces a new model that improves prediction accuracy of wave decay and drag coefficient.

Contribution

It presents a novel analytical model for wave attenuation by mangroves that accounts for stem arrangement and improves upon previous models in predicting wave decay and drag coefficient.

Findings

Larger incident wave height and submergence ratio increase wave decay.

The new model better predicts drag coefficient and wave attenuation compared to previous models.

Predicted results align well with experimental data.

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.