A weir set on the lip of a rock slope
The Kamisaibara Power Station Ikego River Intake Weir is a concrete gravity weir of 1930 in the Junigawa district of Kamisaibara, Kagamino, Okayama Prefecture, and it was listed as a Registered Tangible Cultural Property on 29 November 2006. It sits at the upper end of the Ikego channel, which carries water down to join the Tenno channel serving the station.
The weir is 12 metres long and 3.1 metres high, with a downstream face raked at a slope of one to about one tenth, close to vertical. Its surface is laid in diagonal stone coursing. What separates it from the station's other tributary weir is where it was put: on the crest of a steep rock slope, a position that gave the builders somewhere for construction water to drain away while the concrete was going in. Choosing a site for the convenience of the pour, and then living with that site for a century, is a very 1930 kind of decision.
An arch-shaped opening is cut through the body of the weir towards the left bank. This is a sand flush outlet. Open it and the accumulated gravel behind the weir goes downstream under its own weight instead of being dug out by hand.
Why the weir was registered
The Kamisaibara Power Station Ikego River Intake Weir holds registration number 33-0143. Nine structures of this station were accepted together on 29 November 2006, all of them under the criterion that they contribute to the historic landscape of the country.
Registration, which dates from 1996, applies to buildings and works still in service. It obliges an owner to give notice before substantial alteration rather than to keep a structure frozen, so a Registered Tangible Cultural Property normally carries on working. Okayama Prefecture records all nine of these as facilities in current use.
The Ikego rises in the high ground below Ningyo Pass on the Okayama side of the prefectural border, a plateau that also feeds the headwaters of the Yoshii. Capturing it meant taking the channel a long way north of the powerhouse, and the length of that detour is a measure of how badly a run-of-river scheme needs every litre it can find. Kamisaibara Power Station is rated at 2,700 kilowatts, gathered from the main river and three tributaries.
What to look at
The arch of the sand flush outlet is the detail to find. An arch is not the obvious shape to cut through a concrete weir, since a rectangular gate opening is simpler to form and simpler to close. The arch spreads the load around the opening and lets the section above it stay thin, which matters on a weir this short and this tall in proportion.
Then step back and look at the ground under it. The rock face falls away below the structure at a pitch that would make any modern contractor call for scaffolding. In 1930 that same pitch was read as an advantage, because water and spoil ran off it without help.
Compare the near vertical downstream face here with the gentler stone slope of the Akawase weir a few kilometres away. Both were built in the same year for the same station, and the difference is entirely a response to the ground. The Kamisaibara Power Station Ikego River Intake Weir is the tallest of the station's three tributary intakes, and the shape follows from that.
Visiting
This is part of an operating generating scheme. No admission is charged, no opening hours are published, and the intake structure stands 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. Photography is worth raising on the same call.
The site lies in the northern part of Kamisaibara, on the way towards Ningyo Pass and the Tottori border, in country served by National Route 179. By public transport, take the JR Kishin Line to Tsuyama Station or Inno-sho Station and change to the Chutetsu Hokubu Bus service towards Okutsu Onsen and Ishigoshi; Kagamino town publishes the timetables. The last stretch is on narrow forest lanes with no footway, and the ground beside the weir drops steeply, so keep well back from the edge.
- 📍 Plan Your Visit to Okayama
- Find tours, activities & transport passes near Kamisaibara Power Station Ikego River Intake Weir
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Q&A
- How tall is the Kamisaibara Power Station Ikego River Intake Weir?
- It is 3.1 metres high and 12 metres long, the tallest of the station's three tributary weirs, with a downstream face close to vertical and a diagonally coursed stone surface.
- What is the arched opening in the weir?
- A sand flush outlet, cut through the body of the weir towards the left bank. Opening it lets accumulated sand and gravel wash downstream instead of having to be removed by hand.
- Why was the Kamisaibara Power Station Ikego River Intake Weir built on a steep slope?
- The Agency for Cultural Affairs record notes that the position at the top of a steep rock slope also suited drainage during construction, which mattered when concrete was being placed in a remote valley.
- Where does the water go from here?
- Into the Ikego channel, which passes a settling basin about 40 metres downstream and then joins the Tenno channel feeding the station's head tank.
- Is the weir still working?
- Yes. Okayama Prefecture records all nine registered structures of this station as facilities in current service, and Chugoku Electric Power lists the station at 2,700 kilowatts.
Basic Information
| Name | Kamisaibara Power Station Ikego River Intake Weir |
|---|---|
| Location | Junigawa, 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 3.1 metres, diagonally coursed stone face, arched sand flush outlet; with sluice gate structure |
| 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 Ikego River Intake Weir
- https://kunishitei.bunka.go.jp/heritage/detail/101/00006056
- Cultural Heritage Online, Agency for Cultural Affairs: Kamisaibara Power Station Ikego River Intake Weir
- https://online.bunka.go.jp/heritages/detail/143321
- 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