Research on geoenvironmental dynamics of coastal and alluvial lowlands

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In this study, we discussed on the evolution and geo-environment of alluvial and coastal lowlands in relation to natural disasters and environmental change. The landforms of the alluvial lowlands have developed in response to sealevel and climate changes during the postglacial age.The Tsugaru, Noubi and Echigo plains were the target plains, and the sedimentation rate and the evolution process of the alluvial lowlands were discussed by 10^3 or 10^2 years.As a result, it was found that the eruption of Towada had a great influence on the geo-environmental change in the flood plain formed by the Iwaki river and its tributaties. The aggradation of flood plain sediments in the Nobi and Tenryu plains progressed after the culmination of the Holocene transgression. In the Echigo plain, the rate of the sedimentation is almost equivalent to the Holocene sealevel rise. The sedimentation rate of natural levees in the Nobi plain is about 10 times larger than that of the flood basin.Flood condition a … More nd micro-landforms of the flood plain were studied about in the plains of Thailand and Java. Flood level based on the images of RADARSAT was analyzed in relation to the topography. Based on the analysis, good relationship between flood condition and the seasonal variation of the paddy-rice planting pattern were clarified in the flood plain of central Thailand.Landform classification based on SRTM-DEM data and satellite images were done in the Thu Bon alluvial plain, central Vietnam. Good relationship between the flood condition and the topography of the plain were clarified and shown with GIS. Furthermore, formation of the acid sulfate acid soil in the Lower Central Plain, Thailand was discussed. And it was made clear that the distribution of acid sulfate soils is related to the distribution of mangrove forest which developed along the extended coastline during the middle Holocene embayment.As mentioned above, time and spatial dynamics in relation to the formation of alluvial lowland were clarified, and the relationship between the geo-environmental dynamics in alluvial and coastal plains and various issues as to natural disasters and human habitation in the lowlands were shown in this study. In addition, several researches for this study were done particularly in Southeastern Asian areas and the result may be able to contribute to the local people. Less