Experiment on solitary wave passing through coastal vegetation in waterlogged condition

Abstract

Large scale experiments were conducted to assess the energy dissipation of Tsunami waves passing through the coastal vegetation. In order to simulate the arrival of a large Tsunami wave (hereafter the second tsunami wave) before recedence of the previous small wave (hereafter the first tsunami wave), as observed in certain parts of Sri Lanka during the 2004 Indian Ocean Tsunami, experiments were conducted under waterlogged vegetation conditions. The first part of the study was to substantiate the experimental results with the theories available for solitary wave characteristics. The second part discussed the energy dissipation of solitary waves through coastal vegetation in waterlogged conditions. The experiments carried out in a 20 m (L) x 0.8 m (W) x 2 m (D) flume equipped with a programmable wave synthesizer. The model scale was taken as 1:12.5. Two types of vegetation that are found in Sri Lankan coastal belt were modeled. The difference between the two types is the stem height, branch and leaf configuration. Type I plants are taller than type II plants. Therefore the resistance of branches and leaves to the second tsunami wave passing over the inundation by the first tsunami wave would be possible in type II vegetation. The results indicated that there was a good agreement between experimentally generated solitary waves with the theory for traveling of solitary waves at constant water depth. Depending on the location of prominent wave breaking, the amount of energy dissipation by the vegetation model varied. The vegetation model dissipated higher amount of wave energy of non breaking solitary waves than the solitary wave breaking before or within the vegetation model. Irrespective of the wave input and the location of prominent wave breaking, when the water depth was just below the height of branches and leaves, the model of branches together with leaves reduced more solitary wave energy than the model of stems.