Shohoji River Minamizawa No. 9 Isseki Dam

Shobojigawa Minamisawa Dam No. 9-1

The south wing of Dam No. 9-1 curves rather than runs straight as it joins the bank, a deliberate move for strength, letting the wall shed the load of sediment pressing against it.

The Shobojigawa is a mountain tributary of the Kuratsugawa in the Mogami river system, running past Shimo-Oginoto in Tendo City. Following the flood of 1913, the prefecture placed stone dams and current-control works through the north, Tanuki and south branches of the valley between 1922 and 1927, this dam among them.

Roughly sixty-five metres below No. 8. Its downstream face carries a stone-paved apron. The body is thickened, and the south wing is curved where it meets the bank, giving the whole a solid, braced form.

Why It Matters

In all, the works comprise sixteen dams on the north branch, three on the Tanuki, and ten on the south, joined by gabion structures that steer the current. The idea was not one great wall but many modest ones in series, easing the gradient of a scoured torrent little by little.

The stonework is tanizumi, laid on the diagonal to spread the load, and nerizumi, mortared at the joints so the wall acts as one. Diagonal coursing of this kind resists water and earth pressure and suits a dam set in a fast mountain stream. Both faces are given a 3-bu batter, a nearly upright lean of about one in 3.3.

The dams were entered on the register of tangible cultural properties in 2005, valued as a record of early modern sabo engineering and as part of the fabric of the ravine landscape.

Seeing It Today

This is rough country on the edge of Tendo City, with no paved walkways. Visit only after checking the weather and the flow, and keep within safe bounds. Up close you can read the worked faces of the masonry, still holding water after a century, and the moss on the stone.

The dam measures 15 metres along its crest and stands 3.0 metres high. It belongs to the Minamisawa branch and was completed in 1926.