Intrabasinal Watershed between Mukogawa and Kakogawa River Systems in the Western Part of the Sanda Basin, Hyogo Prefecture, West Japan

Abstract

The Mukogawa River, one of major rivers in Hyogo Prefecture, west Japan, flows from the southwestern part of the Sasayama Basin to the Osaka Bay through the Sanda Basin and more downward mountaineous areas of the Rokko Uprift Zone. The intrabasinal watershed between river systems of the Mukogawa River and its westward Kakogawa River has been poorly known in the western part of the Sanda Basin. In the part, the 4.9 km long Ainogawa River flowing eastwards into the Mukogawa River is close to the 4.3 km long unnamed river, a tributary of the Tojyogawa River flowing southwards into the Kakogawa River. The exact boundary between these two river systems in the Sanda Basin has been traced through detailed field observation and the decipherment of topographic maps and an aerial photo. This intrabasinal watershed is described and discussed topographically in this paper. It is inferred to have migrated gradually eastwards mainly by a marked difference of the floor gradient between these two small rivers as well as between the Mukogawa River in the Sanda Basin and the Tojyogawa River. The degree and rate of the migration in the near future depend more largely on artifici aclontrols than on natural environmental factors including tectoni cmovements.