Coastal protection against perennial erosion and to combat extreme events like storm surges and tsunamis is vital. The 2004 tsunami is one of the deadliest tsunamis, the severe impact of which on human lives and to the structures was most unexpected. Later from the field investigation, the role of coastal vegetation in minimizing the inundation height and distance along the coast had gained special attention. The post tsunami studies have provided enough evidence that mangroves had behaved as natural wave attenuators. The projected climate change impacts have forced researchers to focus on the effectiveness of vegetation, termed also as green belt as an eco-friendly protection measure to combat flows inland and also facilitate sustainable coastal development.
The objective of the present study is to understand the energy dissipation characteristics of the vegetation exposed to extreme events like storm surges and tsunamis through experimental and numerical investigations. Slender polyethylene cylinders representing rigid vegetation models with a scale ratio of 1:40 were adopted for the experimental investigation. Different flow characteristics, viz., monochromatic waves, bi-chromatic waves, solitary waves, elongated solitary waves and tsunami like bores are considered in the present study to investigate in detail the flow interaction with the different widths of vegetation belt. One of the important conclusion drawn from experimental study till date is that for the solitary and elongated solitary wave interacting with vegetation has shown an energy reduction of about 25% for a 40m (Prototype scale) vegetation belt. The wave height attenuation was found to be higher for the near submergence condition.
The New Rummy-RANS3D (open source) has been used to carry out the detailed numerical investigation. The microscopic numerical approach has been considered to obtain an insight of the wave – vegetation interaction phenomenon. The validation of the numerical with experimental results has been done and the agreement is found good. Further, the numerical investigation with spacing variation along shoreward (SSV) and alongshore (ASV) has shown that the closer the spacing more efficient is the flow attenuation for both cases. The breakdown of shedding vortex was observed to be higher for closer spacing between the individual stems. Comparing SSV and ASV, the breakdown of shedding vortex is found to be higher for the closer spacing of SSV. In conclusion, this research will bring out different aspects of wave vegetation interaction and the important characteristics that need to be considered while setting up the costal vegetation as a protection measure to combat effects due to extreme coastal hazards.