There were many offshoots of old Kiso River in the Nobi plain. Most of the areas along the offshoots of old Kiso River have been developed as farmland, industrial land, housing land, etc. Those developed lands will have the possibility of potential risks of flood due to the lower ground and liquefaction due to the existences of loose sandy layer as well as shallow underground water. The findings are shown from the historical viewpoint in this paper.
This paper presents a qualitative study from historical viewpoint about the present status and potential risks of the ground along the old river alignments and their hinterland of old Kiso River in the Nobi plain. The substantiation and other information of this study has been drawn from the field reconnaissance and the search for old books rather than the technical data obtained from laboratory tests or engineering analysis.
It was mentioned in some literatures that old Kiso River had many offshoots in the 16th century as shown in Figure 1, namely Ishimakura River, Hannya River, Azai River, Kuroda River, Sakai River, Ryounai River, Ajika River, Saya River, etc. The 1st offshoot, 2nd offshoot, 3rd offshoot and 4th offshoot of old Kiso River was identified as Ishimakura River, Hannya River, Azai River and Kuroda River, respectively. Furthermore, Ajika River, Ryonai River and Sakasa River were also the offshoots of old Kiso River. It was known that Sakai River was a main flow of old Kiso River up to the middle of 16th century, which was also the border line between Owari Clan and Mino Clan. However, the alignment of old Kiso River has been changed from the flowing alignment of Sakai River to the present alignment due to a mega-flood occurred in 1586.
