Reevaluation of Shingen-tsutsumi based on inundation flow simulations with special focus on the flood control facilities along the Midai River

Abstract

In the western part of the Kofu Basin, embankments often called Shingen-tsutsumi are distributed around the confluence of the Kamanashi River and the Midai River. Although there has been a great deal of historial research on Shingen-tsutsumi, few attempts have been made to clarify their concrete roles based on natural sciences. Therefore, this paper reevaluates the flood control system of Shingen-tsutsumi based on inundation flow simulations. We arranged each embankment (Ishitsumidashi, Shirane-Shogigashira, Tatsuoka-Shogigashira, Horikiri, Ryuo banks, and Kasumi embankments) on an old digital elevation model (DEM) produced by smoothing the present DEM. Then, we performed inundation flow simulations using a dynamic wave model to calculate the expanse of the Midai River using each old DEM. In these simulations, we reproduced the previous flows of the Midai River, and evaluated the flood control ability of each Shingen-tsutsumi embankment. We concluded that the flood control system of Shingen-tsutsumi would not have been effective if the Ishitsumidashi, Shirane-Shogigashira, Horikiri, Takaiwa, and Ryuo embankments had not been arranged in this order. We therefore speculated that these embankments were constructed before the modern age within a short period. This finding differs from historical studies of Shingen-tsutsumi.