The Characteristics of the Floods and the Defense-Countermeasures from a Flood History Point of View on the Plains in the Lower Courses of the " Tokaigata-3 Rivers "

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In this study, 'Toukaigata-3 Rivers' mean the rivers of the Fuji River, the Ohi River and the Tenryu River in Shizuoka Prefecture which have experienced floods many times in the historic times. For the developments of the plains in the lower courses of these rivers, there were a lot of gory struggles between floods and inhabitants without a break. In this study, the writer made researches in the floods on the plains of these rivers from a flood history point of view, and intended to make clear the characteristics of the floods in these rivers.According to the investigation on the floods since the beginning of the 16th century, the plains in the lower course of the Fuji River, the Ohi River and the Tenryu River suffered floods over 60, 130 and 100 times respectively. In the Fuji River, among those floods over 60 times, it became clear that there were very important two years holding the key to the solution of the questions of the flood history.One of them is the year which the huge embankments, 'Kariganezutsumi' were constructed along the left-hand side, by three generations of the father and child of Furugouri-Sigetaka, -Sigemasa and -Shigetoshi in 1674. Before this year, most of the floods flowed on the left-hand side plain, but after that, the floods were shifted to overflow on the right-band side plain. The other one was the year which the big earthquake, the so-called 'Ansei-Tokai-Jisin' , occurred in 1854. On the occasion of this earthquake, the active fault happened to occur along the riverbed from north to south, and the ground of the western side uplifted along the fault relatively. After that, the floods shifted again to the left-hand side plain, On the floods of the Fuji River and 'Toukaigata-3 Rivers, the writer has contributed a paper.