Where the water is taken out of the Yoshii
The Kamisaibara Power Station Yoshii River Intake Weir is a concrete gravity weir of 1930 built across the Yoshii River in the Heisakubara district of Kamisaibara, Kagamino, Okayama Prefecture, and it was listed as a Registered Tangible Cultural Property on 29 November 2006. It is the head of the whole scheme. Everything else the station owns exists because water is diverted here.
The structure is 30 metres long and 2.6 metres high, faced in stone. Those numbers sound modest until you notice what the builders did not have to do. Bedrock breaks the surface in the riverbed and along both banks at this point, and the weir was seated straight onto it. A run-of-river scheme lives or dies on foundation costs, and the site was chosen because the foundation was already there.
On the right bank sit two things that are usually the first parts of an old weir to disappear. One is a sluice gate structure with six openings, which is what actually admits water to the channel and lets the operator shut it off. The other is a fish ladder built at a gradient of six tenths. Both survive complete, which is unusual on a working weir approaching a century of service.
Why the weir was registered
Nine structures belonging to this station were entered on the register on the same day in 2006, and the Kamisaibara Power Station Yoshii River Intake Weir carries registration number 33-0140, the first of the run. The criterion applied to all nine was that they contribute to the historic landscape of the country.
Registration is a lighter instrument than designation. Introduced in 1996, it covers buildings and works that are still earning their keep, and it asks the owner to give notice before major alteration instead of freezing the fabric. A Registered Tangible Cultural Property can go on working, and Okayama Prefecture records every one of these nine as a facility in current service.
The weir also fixes a date in the history of the upper Yoshii. Chugoku Godo Denki, a predecessor of Chugoku Electric Power, worked its way down this valley between 1920 and 1932, building Iri in 1920, Heisakubara in February 1928, Kamisaibara in July 1930 and Okutsu in February 1932. This weir belongs to the third of those campaigns, and it stands only a short distance west of the Heisakubara powerhouse whose used water it collects again.
What to look at
The stone facing repays close attention. A gravity weir does not need a stone skin to stand up; the concrete behind it does the work. The facing was applied because a raw concrete face in 1930 weathered badly and because masons were cheaper than formwork carpenters in a valley this remote.
Follow the right bank and the logic of the layout unfolds in about 50 metres. Water passes the six sluice openings, turns out of the river, and immediately enters the confluence basin next door. The fish ladder runs alongside on its own gentle slope. Three quite different flows, one for generation, one for fish, one for surplus, are separated within a few steps of each other.
In low water the exposed bedrock that carries the Kamisaibara Power Station Yoshii River Intake Weir is visible on both banks, grey and jointed. It is the clearest explanation on site of why the engineers stopped at this particular bend.
Visiting
The weir is part of an operating power scheme. There is no admission charge, no ticket office and no published opening time, and the sluice gate structure is inside the operator's fence.
Okayama Prefecture asks anyone wanting to view the facilities to arrange it in advance with the Tsuyama Power Office of Chugoku Electric Power, on 0868-27-0275. Raise the question of photography on the same call.
Heisakubara lies in the northern part of Kagamino, close to the Tottori border, on National Route 179 between Tsuyama and Ningyo Pass. By public transport, take the JR Kishin Line to Tsuyama Station or Inno-sho Station, then the Chutetsu Hokubu Bus service running towards Okutsu Onsen and Ishigoshi; Kagamino town publishes the timetables. River levels rise fast after summer rain, and the banks here are steep, so stay on the road when the water is high.
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Q&A
- Can I visit the Kamisaibara Power Station Yoshii River Intake Weir?
- The weir can be seen from the valley road, but the sluice gates and the channel entrance stand inside the operator's fence. Okayama Prefecture gives 0868-27-0275, the Tsuyama Power Office of Chugoku Electric Power, as the contact for arranging a look at the facilities.
- How big is the Kamisaibara Power Station Yoshii River Intake Weir?
- It is 30 metres long and 2.6 metres high, a concrete gravity weir with a stone-faced surface, seated on bedrock exposed in the riverbed and the banks.
- Does the weir have a fish ladder?
- Yes. A fish ladder built at a gradient of six tenths survives on the right bank, alongside a sluice gate structure with six openings. Both date from the original work of 1930.
- Is the weir still in use?
- Yes. It still diverts water for Kamisaibara Power Station, which Chugoku Electric Power lists at an output of 2,700 kilowatts on the Yoshii River system.
- What else can I see nearby?
- The confluence basin of the same station sits immediately on the right bank, and the Heisakubara powerhouse of 1928 is a short distance upstream. Both are registered in their own right.
Basic Information
| Name | Kamisaibara Power Station Yoshii River Intake Weir |
|---|---|
| Location | Heisakubara, 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 30 metres, height 2.6 metres, stone-faced; with fish ladder and sluice gate structure of 6 openings |
| Owner | Chugoku Electric Power Co., Inc. |
| Public Access | Operating facility. Visible from the valley road; 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 Yoshii River Intake Weir
- https://kunishitei.bunka.go.jp/heritage/detail/101/00006053
- Cultural Heritage Online, Agency for Cultural Affairs: Kamisaibara Power Station Yoshii River Intake Weir
- https://online.bunka.go.jp/heritages/detail/141818
- 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