Ashiyasu Sabo Dam

Japan's First Cement Sabo Dam

The Ashiyasu Sabo Dam (芦安堰堤) is an erosion control (sabo) dam on the Midai River at Ashikura, Ashiyasu, Minami-Alps City, Yamanashi Prefecture, begun in 1916 and said to be the first sabo dam in Japan built with cement, and was registered as a Registered Tangible Cultural Property (structure) on September 3, 1997. It was raised between 1924 and 1926 (Agency for Cultural Affairs).

The Agency for Cultural Affairs records a dam with a gravity lower stage and an arch upper stage, 22.6 metres high and 66.6 metres long; registration number 19-0017, owned by Yamanashi Prefecture.

Taming the Midai River

The Japan Society of Civil Engineers explains that the Midai River, a right tributary of the Kamanashi in the Fuji River system, is a steep, eroding torrent with an average gradient of 7.2 per cent. Close to the Itoigawa-Shizuoka Tectonic Line, its landslides have built one of Japan's largest alluvial fans. Home Ministry sabo works began in 1883 on the advice of the Dutch engineer Mulder and others, but most of their dry-stone dams were destroyed by repeated debris flows.

Yamanashi Prefecture notes that, with the dry-stone works mostly broken or washed away and judged unreliable, a stronger dam using concrete seems to have been planned. Minami-Alps City records that it was built as a Home Ministry sabo project and has been managed by Yamanashi Prefecture since 1932.

Value as a Registered Cultural Property

The Ashiyasu Sabo Dam was registered as a structure that has become a model of design. The Agency for Cultural Affairs notes that it was built directly by the Home Ministry as Japan's first sabo dam using cement, that its arch-over-gravity form is rare, and that its mortared stone facing shows the character of its time. In 2003 it was recognised with others in the Midai River dams as a Civil Engineering Heritage site (Japan Society of Civil Engineers).

What to Look For

According to Yamanashi Prefecture, the gravity dam completed in 1918 was almost filled with sediment by that summer's floods. Because the foundation was firm and raising the dam would greatly increase its effect, the gravity dam was built up to the top of its wings and an arch dam set on it, with steel reinforcement where the arch footing extended beyond the old dam.

At the Ashiyasu Sabo Dam you can see the curving arch stage resting on the gravity stage below.

Visiting

The Ashiyasu Sabo Dam is a working sabo structure in the mountains of Ashiyasu, Minami-Alps City, about 12 kilometres from the Shirane interchange of the Chubu-Odan Expressway (Yamanashi Infrastructure Guide).

As it stands in a mountain stream, keep away after heavy rain and view it from a safe place. Enquiries go to Yamanashi Prefecture's Chuhoku Construction Office (055-224-1660).