FLOOD AND TSUNAMI FLOW IN RELATION TO THE LANDFORMS OF COASTAL AND ALLUVIAL LOWLANDS-CASE STUDY IN HAT YAI AND BANDA ACEH PLAINS

Abstract

Flood control is a very important issue of the environmental management in the alluvial and coastal plains. For the detail management, it is necessary to know the behavior of the flooding on the plains. Micro landforms of these plains are closely related to the flow and inundation depth of floods. Landforms of an alluvial plain are roughly classified into three units. alluvial fan, floodplain and delta. Landforms of these units are further classified into micro landforms as natural levee, flood basin, paleo-river channel, beach ridges and so on. The places on a higher micro landforms are generally flood free places or the places where the flood depth is shallow. On the contrary, flood water concentrate on the place of the lower micro-landforms as flood basin or back swamp and inundation depth is deep in the areas. Coastal areas as coastal plain or delta plain are subjected to the inundation by tidal surge or tsunami. Regional differences of the landforms of the coastal plain are also related to the difference of flood condition in a plain. Hazard map or risk map for the flood disasters should be taken the characteristics of micro landforms into consideration.