Abstract
We investigated a 20 m-wide mangrove forest that was said to have mitigated damage from the 2004 Indian Ocean Tsunami in Godawaya on the southern coast of Sri Lanka. The narrow mangrove forest along a lagoon, which was located on the landward-side of a sand dune, was observed to weaken the tsunami wave that came over the sand dune area between the sea and the lagoon. A family living inland on the opposite side of the lagoon from the mangrove forest said that the forest appeared to reduce the force of the tsunami that came over the lagoon and hit their house. We investigated the characteristics of the mangrove forest which mitigated the tsunami damage and determined whether the mangrove trees that were uprooted or broken by the tsunami were swept inland had caused extensive damage. To determine whether the mangrove diminished the strength of the tsunami at the time the tsunami hit, we attempted to compare inundation height and/or the damage caused by the tsunami between two areas along the lagoon: one with mangroves, and another without. Despite not being able to locate a site without mangrove forest, we identified one case in which the tsunami swept across an area of sand dunes and a mangrove forest before hitting a house. Based on this evidence we propose that mangroves are important for reducing the force of tsunamis and should be maintained as barriers against tsunamis, even in instances where the mangroves are not facing the open sea, particularly in areas where the original coastal vegetation has been lost due to anthropogenic pressure.
https://ror.org/044bma518 
