Granite Along the Riverbank at Okutsugawanishi
The Okutsu Power Station Main Building Retaining Wall is a stone and reinforced concrete structure of 1932 at Okutsugawanishi in Kagamino, Okayama Prefecture, and it was added to the national register of Registered Tangible Cultural Properties on 18 October 2006 under number 33-0126.
The registration covers two walls rather than one. Behind the powerhouse, on its western side, a retaining wall holds back the slope. Along the boundary with the Yoshii River, a second wall armours the bank. Together they extend about 185 metres, and the Agency for Cultural Affairs records the whole as a single site rather than as separate items.
The stone is granite, squared and set diamond-wise in the bond that Japanese masons call tanizumi. Turning each block through forty-five degrees puts the joints on the diagonal, which lets a wall follow a changing slope without the horizontal courses stepping awkwardly at every break. Mortar binds the blocks, so this is not dry stone: it is masonry built to stay watertight against a river that rises fast after mountain rain.
A Handrail and a Tunnel Mouth
Two details break up the length of the riverside wall.
The first runs along its top. A reinforced concrete balustrade 0.85 metres high finishes the revetment, a low parapet that reads as a handrail from a distance. Concrete used decoratively above granite masonry is a period marker in itself, the newer material sitting on the older craft.
The second is set roughly at the centre of the wall: the portal of the spillway tunnel. When the canal delivers more water than the turbines can take, the surplus has to go somewhere, and it goes through this opening back into the Yoshii. The tunnel mouth is the only point where the wall admits anything at all, and it is a reminder that the Okutsu Power Station Main Building Retaining Wall is not decoration. It is the edge where an engineered water system meets a natural river, and both directions of flow had to be accounted for.
Why a Wall Is on the Register
The register of Registered Tangible Cultural Property was established in 1996 for structures more than fifty years old that remain in service, and Okayama Prefecture's cultural properties division sets out three criteria for entry. The Okutsu components were taken up under the first, contribution to the historic character of the national landscape, and were listed together in October 2006.
The Agency for Cultural Affairs is direct about the reason in this case: the walls form the historic scene of a modern power station together with the main building. That is a judgement about setting rather than about the wall as an isolated object. A powerhouse standing on a bare cut slope would look like any twentieth-century industrial shed. The granite terraces and the concrete parapet give the site its 1930s character, and the description of the group ties the two together.
Okutsu is a canal-type station on the upper Yoshii, rated by Chugoku Electric Power at 7,500 kilowatts, and its registered components run from intake weirs high in the mountains down to this point. The wall is where that sequence ends.
The Most Approachable of the Group
Most of the registered Okutsu structures sit deep in forest with no road frontage. This one is different. The Okutsu Power Station Main Building Retaining Wall stands at the plant itself in the Okutsugawanishi district, close to the Okutsu Onsen area on Route 179, and the stonework is legible from public ground beside the river.
Driving is straightforward: roughly 25 minutes north from the Innosho interchange of the Chugoku Expressway along Route 179 toward Kurayoshi. From JR Tsuyama Station, a Chutetsu Hokubu bus reaches the Okutsu Onsen area in about an hour, though services are few, so check departure times before relying on them.
There is no entry to the power station and no visitor facility of any kind, and the land inside the walls is operational. Photography from public roads and the riverbank is unrestricted, and low winter light across the diagonal joints shows the masonry pattern better than summer sun does. Access details were confirmed in September 2026.
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Q&A
- What exactly does the Okutsu Power Station Main Building Retaining Wall consist of?
- Two walls registered as one site: a retaining wall on the western side of the powerhouse, and a revetment wall along the boundary with the Yoshii River. Their combined length is about 185 metres.
- How was the Okutsu Power Station Main Building Retaining Wall built?
- In mortared granite masonry laid in the diagonal tanizumi bond, combined with reinforced concrete. A concrete balustrade 0.85 metres high runs along the top of the riverside wall.
- What is the opening in the middle of the Okutsu Power Station Main Building Retaining Wall?
- It is the portal of the spillway tunnel, which returns surplus water from the canal system to the Yoshii River when the flow exceeds what the turbines can use.
- When was the Okutsu Power Station Main Building Retaining Wall registered?
- On 18 October 2006, as a Registered Tangible Cultural Property (Structure) under number 33-0126. The walls themselves date from 1932.
- Can the Okutsu Power Station Main Building Retaining Wall be seen without special permission?
- Yes, from outside. The walls are visible from public roads and the riverbank near Route 179 in the Okutsugawanishi district. There is no entry to the power station grounds, but viewing and photography from public ground are unrestricted.
Basic Information
| Name | Okutsu Power Station Main Building Retaining Wall (奥津発電所本館擁壁) |
|---|---|
| Location | 560 Kanda, Okutsugawanishi, Kagamino, Tomata District, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure), register no. 33-0126 |
| Year Designated | Registered 18 October 2006 (Heisei 18) |
| Quantity | 1 site |
| Dimensions | Total length approx. 185 m; reinforced concrete balustrade 0.85 m high on the riverside wall |
| Owner | The Chugoku Electric Power Co., Inc. |
| Public Access | Operating hydroelectric infrastructure. No entry to the grounds. Visible from public roads and the riverbank. |
References
- National Database of Cultural Properties, Agency for Cultural Affairs: Okutsu Power Station Main Building Retaining Wall
- https://kunishitei.bunka.go.jp/heritage/detail/101/00005916
- Okayama Prefecture, Cultural Properties Division: the cultural property registration system
- https://www.pref.okayama.jp/page/505223.html
- The Chugoku Electric Power Co., Inc.: list of hydroelectric stations
- https://www.energia.co.jp/energy/general/water/water_all.html
- Kagamino Town official website
- https://www.town.kagamino.lg.jp/
Last verified: 2026.09.09