The Shidomae River, which originates in the Ou Mountains, Mount Ugo Asahi, and Mount Mocco, is the largest tributary of the Tatsu River, which is the source of the Shizukuishi River, and the Arasawa, Daichizawa, and Koshidomaezawa rivers all flow into the Tatsu River. In contrast to the Tatsu River, which has a steep drop in elevation, the Shidomae River is characterized by a generally gentle slope up to its upper reaches. 