Flood Risks and Their Management in Urban Japan—Modeling Inner Flooding in Tsushima City, Tokai Region

Abstract

The topography of the Japanese archipelago is largely mountainous with only narrow strips of lowland. These lowland plains are exposed to various types of flooding such as river floods due to rapid runoff from steep highlands as well as inner (urban) flooding due to water retention. In this chapter we look at the issue of flood disasters, describing the causal structure of flood risk along with the concepts and processes of the phenomena of urban flooding. There already exists a range of infrastructural and software measures to attempt to mitigate the occurrence and resulting damage of urban flooding. In order to discuss the risks of floods in lowland urban areas, we review the processes of the Tokai flood of 2000 by conducting a series of inundation analyses of the downtown area of Tsushima city, where a combined sewerage system is in place. These results provide a better understanding of the process of urban flooding as well as effective mitigation measures.