A small weir on a tributary, faced in granite
The Kamisaibara Power Station Akawase River Intake Weir is a concrete gravity weir of 1930 in the Ishigoshi district of Kamisaibara, Kagamino, Okayama Prefecture, and it was listed as a Registered Tangible Cultural Property on 29 November 2006. It stands about 1.5 kilometres west of the station's main weir on the Yoshii River, at the upper end of the Akawase channel, which later joins the Tenno channel.
At 12 metres long and 2.3 metres high it is one of the smallest structures in the group, and it was placed directly on bedrock. The face is granite laid in the diagonal coursing that Japanese masons call tanizumi, in which each block is set on point so that the joints run as a diamond grid rather than in level beds. On a curved weir crest that pattern absorbs the slight changes of plane far more easily than horizontal courses would.
At the intake on the left bank there is a housing for a screen that strains leaves, branches and other debris out of the water before it enters the channel. On a tributary that drains steep forested slopes, a screen is not an accessory. Without it the channel silts and the turbines suffer.
Why the weir was registered
The Kamisaibara Power Station Akawase River Intake Weir was registered under number 33-0142, one of nine structures of the station accepted on the same day under the criterion that they contribute to the historic landscape of the country.
The register was created in 1996 for works that remain in use. It requires an owner to notify the authorities before major alteration rather than to preserve a structure untouched, and a Registered Tangible Cultural Property therefore normally goes on doing its job. Okayama Prefecture lists every one of these nine as a facility in current service.
The reason a tributary weir merits attention is arithmetic. A run-of-river station has no reservoir to fall back on, so the output depends entirely on how much water can be gathered at any moment. Kamisaibara Power Station is rated at 2,700 kilowatts, and it reaches that figure by adding several small catchments to the main river. Three tributary intakes were built in 1930 for that purpose, and this is the westernmost of them.
What to look at
Granite is the point. The Chugoku Mountains are granite country, and the stone used on the face of this weir did not travel far. Compare the joints here with the stone facing on the station's Yoshii River weir and the difference in stone and in coursing shows how much the builders let local supply decide the detail.
Look also at how little the structure asserts itself. The weir is barely wider than the stream, and from a few metres downstream it reads as a low stone step rather than as a piece of industrial plant. That restraint is part of why the group was accepted on landscape grounds.
The channel leaving the Kamisaibara Power Station Akawase River Intake Weir runs on to a settling basin about 240 metres below the point where it joins the Tenno channel, and from there towards the station's head tank. Following the water on the map afterwards makes the layout of the whole scheme much easier to hold in mind.
Visiting
The weir belongs to an operating power scheme. There is no admission charge, no ticket office and no published opening time, and the intake and screen housing lie inside the operator's fence.
Okayama Prefecture asks visitors who want to see the facilities to arrange it beforehand with the Tsuyama Power Office of Chugoku Electric Power, on 0868-27-0275. Ask about photography during the same call.
Ishigoshi is the terminus of the Chutetsu Hokubu Bus route that runs from Tsuyama through Okutsu Onsen, which makes this the easiest of the station's outlying structures to reach without a car. Take the JR Kishin Line to Tsuyama Station or Inno-sho Station and change to that service; Kagamino town publishes the timetables. The approach lanes are narrow and unlit, and snow closes them in midwinter.
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Q&A
- Where exactly is the Kamisaibara Power Station Akawase River Intake Weir?
- In the Ishigoshi district of Kamisaibara in Kagamino, about 1.5 kilometres west of the station's Yoshii River intake weir, at the head of the Akawase channel.
- How big is the Kamisaibara Power Station Akawase River Intake Weir?
- It is 12 metres long and 2.3 metres high, a concrete gravity weir built on bedrock with a granite face laid in diagonal coursing, and it has a sluice gate structure.
- What is the screen at the left bank for?
- It strains leaves, branches and other debris out of the water before the flow enters the channel, which keeps the conduit clear and protects the machinery downstream.
- Can I see it without arranging a visit?
- The weir itself can be seen from the roadside, but the intake and screen housing are behind the operator's fence. For a closer look, contact the Tsuyama Power Office of Chugoku Electric Power on 0868-27-0275.
- Is there a bus to Ishigoshi?
- Yes. Chutetsu Hokubu Bus runs a service from Tsuyama through Okutsu Onsen to Ishigoshi, and Kagamino town lists the timetables on its public transport page. Departures are few, so check the return time before setting out.
Basic Information
| Name | Kamisaibara Power Station Akawase River Intake Weir |
|---|---|
| Location | Ishigoshi, Kamisaibara, Kagamino-cho, Tomata-gun, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (structure) |
| Year Designated | Registered 1930 structure on 2006-11-29 |
| Quantity | 1 weir |
| Dimensions | Concrete gravity weir, length 12 metres, height 2.3 metres, granite face in diagonal coursing; with sluice gate structure |
| Owner | Chugoku Electric Power Co., Inc. |
| Public Access | Operating facility. Visible from the roadside; viewing of the plant by prior arrangement with the Tsuyama Power Office, 0868-27-0275 |
References
- National Cultural Properties Database, Agency for Cultural Affairs: Kamisaibara Power Station Akawase River Intake Weir
- https://kunishitei.bunka.go.jp/heritage/detail/101/00006055
- Cultural Heritage Online, Agency for Cultural Affairs: Kamisaibara Power Station Akawase River Intake Weir
- https://online.bunka.go.jp/heritages/detail/190780
- Okayama Prefecture, Cultural Properties Division: Registered Cultural Properties in Okayama Prefecture
- https://www.pref.okayama.jp/page/detail-50777.html
- Okayama Prefecture: Kamisaibara Power Station Facilities (PDF)
- https://www.pref.okayama.jp/uploaded/attachment/260992.pdf
- Chugoku Electric Power Co., Inc.: List of hydroelectric power stations
- https://www.energia.co.jp/energy/general/water/water_all.html
- Kagamino Town: Route buses and public transport
- https://www.town.kagamino.lg.jp/soshiki/22/2132.html
Last verified: 2026.09.08