Wave transmission and dissipation coefficients of a modified artifical mangrove root system

Abstract

A modified Artificial Mangrove Root System (ArMS) has been proposed to improve the earlier model presented by Eldina (2007). The system may act as an alternative protection structure during the replanting of the young mangrove seedlings while enhancing to protect the marine life and shoreline. ArMS is designed to be porous enough so that it facilitates the exchange of water around it and allows sedimentation. Technically, ArMS acts as a partially or fully submerged breakwater which dissipates the incoming wave energy by the process of breaking, friction and transmission. Laboratory studies with a series of regular waves were conducted for 1row, 2-row, 3-row, 4-row, and 5-row ArMS to determine the hydraulic performance in terms of its efficiency in reducing the incident wave and local velocities in various geometry and wave conditions. Wave attenuation coefficient was investigated by determining the transmission, reflection, and energy loss coefficients. The parameters that affect the wave attenuation are wave length, wave height, water depth, water velocity, and wave period. Funke and Mansard method was adopted to separate the incident and reflected wave. Transmitted waves were measured behind the model structure. Empirical equations to predict transmission, reflection and loss coefficients were derived using multiple linear regression analysis. The analytical predictive equations were developed using H/L, B/L, d/L, and did as the predictive variables. Experimental results showed that wave attenuation depends strongly on the structure geometrical factors. It increases as the width of the structure increase, or exposed to long wave length or period, or when the water depth is relatively large. On the other hand, line configuration of ARMS was found to have lower wave transmission compared to staggered configuration. ArMS gap effect is not significant in affecting wave attenuation performance. In general, the predicted data from derived analytical equations agreed well with the observed data. The comparison between the present and previous ArMS model found that the present model (0.63 porosity) produced lower wave transmission coefficient compared to the previous models (0.94 and 0.95 porosity).