Laboratory investigations on wave attenuation characteristics of Rhizophora Mucronata poir using physical models with bottom friction

Abstract

Species specific hydrodynamic characterization is essential for assessing the suitability of various types of mangroves in coastal protection as the dissipation of wave energy within the mangroves is governed primarily by various aspects which are specific to the species to which they belong. In the present study a specific mangrove species was selected and its wave attenuation characteristics were studied with the help of scaled physical models under controlled wave and vegetation conditions in a laboratory wave flume. The plant was initially identified as Rhizophora Mucronata and the scaled models prepared had the same biomechanical properties as that of the parent plant. Effect of root soil was incorporated in scaled models as bottom friction. Wave heights were measured after the forest models to evaluate the wave attenuation. It was found that wave heights were following the exponential decay equation of Kobayashi et al. (1993) except for the cases which have incorporated bottom friction. For such cases exponential decay equation was modified by incorporating a new parameter ‘d/D50’. Drag coefficients (CD), characteristic of the species were also determined without incorporating and with incorporating the effect of bottom friction of root soil. It is seen that drag coefficients are following an inverse relation with non-dimensional numbers (Re and KC). Empirical relations were developed between CD and a modified Keulegan Carpenter number (modified considering mangrove root submergence and mean particle size) for predicting the drag coefficients specific to Rhizophora Mucronata species for a variety of wave and water level conditions.