Response of coastal vegetation and the need for green belts along the Tamil Nadu coast, India: The December 2004 tsunami experience
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The Indian Ocean tsunami of December 2004 transmitted multiple lessons: whereas certain strips were destroyed in totality, others remained unaffected or practically intact. Detailed post-tsunami field surveys conducted along the coast of Tamil Nadu, south India, in April 2005 and January 2006, confirmed that coastal landforms and vegetation played a significant role in neutralizing the force of virulent waves. Impact on casuarina forests was restricted to a maximum of 25 meters from the dune line. Only frontal casuarina strips were attacked, bent and stripped of their leaves by wave up-rush. Whereas dune creepers and herbs were uprooted, coconut and palm trees remained in position. This phenomenon was verified along the entire Tamil Nadu and Pondicherry coasts. Evidence of minimal damage to casuarina plantations and coconut groves supports the view that biological buffers can serve as efficient energy dissipaters during powerful oceanographic events. Villages located behind dense plantations remained safe. In 2006, natural restoration was identified in the form of rejuvenated and healthy vegetal species. Dune vegetation had bounced back and bent casuarinas had sprouted. The need for a protective coastal buffer zone is proposed. Its levels of effectiveness will depend on a progression of species landward from the shore. Casuarinas should not be located on dunes, but planted further backshore. Herbs – shrubs – bushes - trees form a gradation of species and a natural slope that is inferred to offer protection as natural shelter belt against any eventual extreme event. Future plantation strategies will have to consider natural bio-zonalion rather than haphazard patterns that are observed at present. Green belts are beneficial for several reasons: control of erosion, stabilization of shores, alleviation of wind energy, effective buffer against the force of waves, preservation of biodiversity and advantage in terms of food, shelter and income. It is established that physical and geological processes are intense along the open ocean. Manmade structures thus experience extreme processes as such sites become vulnerable to natural hazards. In comparison, the forested hinterland is sufficiently protected from physical forces as vegetation attenuates energy from onrushing waters. Therefore, elevated coastal stretches with protective vegetation are the only environments where risks due to extreme oceanographic events are modest.
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