The purpose of this study is to confirm the relationship between the coastal topography and the distribution of the extensive damage on the affected area caused by the 2004 Indian Ocean tsunami in the case of Tangalla DS Division, Southern Sri Lanka. By creating maps to depict the distribution of the degree of tsunami damage in Tangalla DS Division in a small area unit (GN Division unit), it is observed that the coasts that were severely damaged are located at the northern side of the cape and that they face the East. By conducting a field survey in the extensively damaged region of Medaketiya, which is one of the GN Divisions located at the northern side of the cape, it is discovered that the tsunami current approached from two different directions. One current that approached from the South might be the current that was reflected at the cape in the South, while the other one approached from the East directly from the ocean. The survey of the ground level and of the trace of the tsunami current in Medaketiya GN Division indicates that the flow of the current toward the northwest direction was blocked by a dune located in its path, and hence, the houses in that area were not severely damaged. Further, the current approaching from the southwest direction flowed toward a lagoon and caused extensive damage to the houses situated there.

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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.

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In this study, the authors examined the location and layout of a forest belt mainly consisting of Japanese black pine in Shonai Coastal Sand Dunes based on their effect of protection against wind erosion. Firstly, we collected data on topography, components and structures of the forest belt, and wind velocity in the area including shifting sand prevention forest, windbreak for cropland, and top of sand dunes where wind erosion is significant. We then organized the data based on their effect of wind protection and determined suitable location and layout of the forest belt. As a result, necessary conditions for the forest belt with adequate wind protection in this area were selected. Furthermore, we were able to confirm that tree height could be used as an indicator when deciding the width of a forest belt.

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To know whether strain gauge transducers can measure the dynamic behavior of tree stems subjected to any horizontal direction loading, we tested the original strain gauge transducer (Moore et al., 2005) and the improved strain transducer that we developed. The improved strain transducer differs from the original transducer mainly in symmetry. When a wooden pole was loaded to any right angle, the strain of the pole transduced by both the original and the improved transducer generally had a cosine relation to the angle between the front of the strain transducer and the loading. Therefore, the strain on a tree stem loaded to any horizontal direction can be estimated by composition of strains in two horizontal directions. Moreover, since the strains of the improved transducer are closer to a cosine curve than those of the original transducer, the improved transducer can estimate the strain on tree stems more accurately than the original.

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We studied the characteristics of slope failure and their temporal change by interpreting aerial photographs taken in May 1977, November 1990, and May 2004 of a granite basin on the island of Yakushima, in Kagoshima prefecture, Japan. Shallow landslides and deep-seated landslides were observed. The total areas of slope failures for the May 1977, November 1990, and May 2004 observations of the basin were about 0.075, 0.049, and 0.128 km² respectively. The aerial photographs taken in May 2004, for which the number of prior heavy rain days was the greatest of the three study periods, showed the highest total area of slope failure. The percentage area of slope failure was greatest for a slope inclination of 40 degrees or more.

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We examined the characteristics of slope failure and their temporal changes, as well as the effect of deforestation on the occurrence of slope failure, for a granite basin on the island of Yakushima in Kagoshima prefecture, Japan, by interpreting aerial photographs taken in May 1977, November 1990, and May 2004. Shallow landslides and deep-seated landslides were observed. The percentage areas of slope failure for May 1977, November 1990, and May 2004 were about 1.0%, 1.2%, and 1.6%, respectively. The aerial photographs taken in May 2004, for which the number of prior heavy rain days was the greatest of the three study periods, showed the highest total area of slope failure. Aerial photographs taken in November 1990, for which the period since deforestation was 16 to 20 years, showed the greatest percentage area of slope failure in the deforested areas.

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