Endurance of the Casuarina coastal forest in southern Sri Lanka against the Indian Ocean tsunami

Abstract

In Hambantota, southern Sri Lanka, we implemented a survey of the damage-mitigating effect and the endurance of the Casuarina coastal forest against the Indian Ocean tsunami that occurred in December 2004. The tsunami struck by passing over the Casuarina forest on the front dune (height of 5.5 m above sea level), but it was unable to pass over the next dune (height of 5 m); therefore, private houses on the inland side of that dune were not damaged. In contrast, in the shallow trough produced by excavation of part of the dune, the tsunami passed over the front dune (height of 3.5 m) and through the Casuarina forest; it destroyed private houses 250m from the shoreline. Although the Casuarina trees growing on the high dune were not damaged, 57% of the Casuarina trees that were directly hit by the tsunami on the trough withered after it passed. However, few tree trunks were broken during the tsunami, so it was suggested that the Casuarina forests had been able to withstand the physical impact of the tsunami.