The last pause before the drop
The Kamisaibara Power Station Head Tank is a concrete water structure of 1930 in the Taruhara district of Kamisaibara, Kagamino, Okayama Prefecture, and it was listed as a Registered Tangible Cultural Property on 29 November 2006. It marks the end of the main channel, about 2.8 kilometres below the confluence basin, and it regulates the quantity of water flowing on to the powerhouse.
Up to this point the water has been travelling nearly level. Below it, the water falls down a penstock to the turbines. That change is why a head tank exists. A turbine's demand rises and falls with the load on the grid, while a channel 2.8 kilometres long cannot speed up or slow down quickly, and the tank absorbs the difference between the two.
The layout runs a curved open channel into a pond of roughly triangular plan, and the pond doubles as a final settling basin. An overflow weir occupies the south side, with a sand flush gate in the middle of the south wall. Together the structure covers 497 square metres, which makes it the second largest of the nine registered structures here after the confluence basin.
Why the head tank was registered
The Kamisaibara Power Station Head Tank carries registration number 33-0146. Nine structures of the station were accepted on 29 November 2006, all under the criterion that they contribute to the historic landscape of the country.
Registration was introduced in 1996 for buildings and works that continue in service. It asks an owner to notify the authorities before major alteration rather than to hold a structure unchanged, so a Registered Tangible Cultural Property usually keeps its original function. Okayama Prefecture records every one of these nine as a facility in current use.
The triangular plan is worth registering because it is a solution to a problem of ground rather than a standard type. On level land a head tank is generally a rectangle. Here the shelf available on the hillside was neither wide nor square, and the pond was shaped to fit what the slope allowed while still giving the water enough surface area to shed its remaining sand. That kind of adaptation is what makes a survey of these upper Yoshii structures rewarding: the same engineering problem is solved differently at each site.
What to look at
Stand where the curved channel opens into the pond and watch the surface. The current visibly loses its edge as the section widens, and fine material begins to drop. The whole settling function of the tank is legible in about ten metres of water.
Look next at the overflow weir on the south side. When the powerhouse reduces its load, the water that is no longer wanted has to go somewhere immediately, and it goes over this crest. The sand flush gate set in the middle of the same wall serves a different purpose, clearing the deposit that has collected on the floor.
Then look downhill. About 250 metres below the Kamisaibara Power Station Head Tank stands the powerhouse, and the penstock connecting them runs straight down the slope between a pair of stone retaining walls that are registered in their own right. Seen from the tank, the whole lower half of the scheme is laid out at once.
Visiting
The head tank is part of a generating station in operation. There is no admission charge, no ticket office and no published opening time, and the structure lies inside the operator's fence.
Okayama Prefecture asks anyone wishing to view the facilities to arrange it in advance with the Tsuyama Power Office of Chugoku Electric Power, on 0868-27-0275. It is worth asking about photography at the same time.
Taruhara is in Kamisaibara, the northernmost district of Kagamino, close to the Tottori border and on the line of National Route 179 between Tsuyama and Ningyo Pass. Travelling by public transport, take the JR Kishin Line to Tsuyama Station or Inno-sho Station and change to the Chutetsu Hokubu Bus service running towards Okutsu Onsen and Ishigoshi; Kagamino town publishes the timetables. The slope between the tank and the powerhouse is steep and wooded, with no path, so view it from the road.
- 📍 Plan Your Visit to Okayama
- Find tours, activities & transport passes near Kamisaibara Power Station Head Tank
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Q&A
- What does the Kamisaibara Power Station Head Tank do?
- It sits at the end of the main channel and regulates how much water flows on to the powerhouse, absorbing the difference between the steady supply in the channel and the changing demand of the turbines. It also settles out remaining sand.
- How large is the Kamisaibara Power Station Head Tank?
- It covers 497 square metres and is built of concrete, comprising a curved open channel leading into a pond of roughly triangular plan.
- How far is it from the powerhouse?
- About 250 metres, with the penstock running down the slope between them. The head tank itself lies about 2.8 kilometres below the station's confluence basin.
- Why is the pond triangular?
- The shape follows the shelf of ground available on the hillside while still providing enough water surface for sand to settle before the flow enters the penstock.
- Can I go and look at it?
- Not without prior arrangement, since it stands inside the operator's fence. Okayama Prefecture gives 0868-27-0275, the Tsuyama Power Office of Chugoku Electric Power, as the contact for viewing the facilities.
Basic Information
| Name | Kamisaibara Power Station Head Tank |
|---|---|
| Location | Taruhara, Kamisaibara, Kagamino-cho, Tomata-gun, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (structure) |
| Year Designated | Registered 1930 structure on 2006-11-29 |
| Quantity | 1 site |
| Dimensions | Concrete, area 497 square metres; curved open channel and pond of roughly triangular plan, overflow weir on the south side, sand flush gate in the south wall |
| Owner | Chugoku Electric Power Co., Inc. |
| Public Access | Operating facility. No public entry; 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 Head Tank
- https://kunishitei.bunka.go.jp/heritage/detail/101/00006057
- Cultural Heritage Online, Agency for Cultural Affairs: Kamisaibara Power Station Head Tank
- https://online.bunka.go.jp/heritages/detail/171362
- 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