Where the Water Leaves the River
The Okutsu Power Station Yoshii River Water Intake Weir is a low overflow dam built in 1932 across the upper Yoshii River in the Kamisaihara district of Kagamino, Okayama Prefecture, and it was placed on the national list of Registered Tangible Cultural Properties on 18 October 2006 as register number 33-0115.
Its crest runs about 34 metres from bank to bank and rises about 3.3 metres above the riverbed. The builders sank no deep foundation. They set the weir straight onto the granite bedrock that surfaces at this point in the valley and let the rock carry the load. Water is designed to pour over the top rather than be held back, so on an ordinary day the entire crest wears a thin, moving sheet.
This is where the whole scheme begins. Okutsu is a canal-type station: rather than impounding a reservoir behind a tall dam, it skims water off the river here and sends it south along an artificial channel, picking up more from side streams as it goes, until enough fall has accumulated to drop onto the turbines. Chugoku Electric Power lists the station's output at 7,500 kilowatts.
A Register Made for Working Things
Japan's register of Registered Tangible Cultural Property dates from 1996 and was designed for buildings and structures more than fifty years old that remain in service. Okayama Prefecture's cultural properties division sets out the three qualifying criteria, and the one applied here is the first of them: contribution to the historic character of the national landscape.
Components of the Okutsu scheme went onto the register together in October 2006, numbered upward from 33-0115. The Okutsu Power Station Yoshii River Water Intake Weir holds the lowest number in that run because it comes first in the water's journey, not because it is the biggest thing on the list. Read the numbers in sequence and you are effectively walking the canal downstream.
One detail deserves care. The Agency for Cultural Affairs records the structural type of this weir as gravity concrete, while the same agency's descriptive note calls it a gravity weir of mortared masonry. Both entries are official. The difference most likely reflects a concrete core behind a dressed stone face, but the database does not say so, and the wording is best treated as unsettled.
The Curved Stair on the Right Bank
Look toward the right bank and the weir stops being a plain wall. A fish ladder peels away from the crest as a run of stepped pools, and its side walls are laid in tanizumi, the diagonal coursing in which squared stones sit corner-up so that the joints read as a lattice instead of level beds. A straight ladder would have been simpler to set out. This one curves, following the shape of the bank and the line of the current, which is the kind of decision that shows the engineers reading the site rather than repeating a standard drawing.
From below, three things register at once: the sheet of water on the crest, the pools stepping down beside it, and the bare rock the whole assembly rests on.
Season changes what you see. In late autumn the flow drops and the stonework stands out sharply. After summer rain the crest vanishes under one continuous fall, and the fish ladder becomes the only place where separate steps can still be picked out.
Reaching the Weir
Kagamino sits in the mountains of northern Okayama and public transport is sparse. From JR Tsuyama Station, a Chutetsu Hokubu bus toward Okutsu Onsen takes roughly an hour to reach the hot spring village, with only a handful of departures each day; the weir lies further north again, in Kamisaihara, so nearly everyone drives. By car it is about 25 minutes from the Innosho interchange of the Chugoku Expressway, north on Route 179 toward Kurayoshi, and then on up the valley.
The Okutsu Power Station Yoshii River Water Intake Weir has no car park, no interpretive sign and no viewing platform. It is live infrastructure owned by Chugoku Electric Power, and the ground immediately around it is operational. Photography from public roads and riverbanks is not restricted, but there is no entry to the structure and no walking the crest. Treat a visit as roadside observation rather than a site tour, and check winter road conditions before setting out, because this valley takes snow. Access details were confirmed in September 2026.
- 📍 Plan Your Visit to Okayama
- Find tours, activities & transport passes near Okutsu Power Station Yoshii River Water Intake Weir
- [ Kurashiki Bikan District & Korakuen Garden Tours ]
Q&A
- What does the Okutsu Power Station Yoshii River Water Intake Weir actually do?
- It raises the level of the Yoshii River just enough to divert part of the flow into the main headrace canal of the Okutsu Power Station. It is the first structure in that canal system, not a storage dam, so water spills over its crest continuously.
- When was the Okutsu Power Station Yoshii River Water Intake Weir built and registered?
- It was completed in 1932, in the early Showa period, and registered as a Registered Tangible Cultural Property on 18 October 2006 under register number 33-0115.
- How large is the Okutsu Power Station Yoshii River Water Intake Weir?
- The crest measures about 34 metres across the river and the structure stands about 3.3 metres high. A stepped fish ladder is attached on the right bank, so the built width is greater than the weir alone.
- Can I go up to the Okutsu Power Station Yoshii River Water Intake Weir, and may I take photographs?
- There is no public entry. The weir belongs to a working power station and the surrounding land is operational. Photography from public roads and riverbanks is not restricted.
- How do I get to the Okutsu Power Station Yoshii River Water Intake Weir from Tsuyama?
- Driving is the practical option: about 25 minutes from the Innosho interchange on Route 179, then further up the valley into Kamisaihara. Buses from JR Tsuyama Station reach Okutsu Onsen in roughly an hour but run only a few times a day and stop short of the weir.
Basic Information
| Name | Okutsu Power Station Yoshii River Water Intake Weir (奥津発電所吉井川取水堰堤) |
|---|---|
| Location | Taruhara, Kamisaihara, Kagamino, Tomata District, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure), register no. 33-0115 |
| Year Designated | Registered 18 October 2006 (Heisei 18) |
| Quantity | 1 structure |
| Dimensions | Crest length approx. 34 m, height approx. 3.3 m, with a stepped fish ladder on the right bank |
| Owner | The Chugoku Electric Power Co., Inc. |
| Public Access | Operating hydroelectric infrastructure. No entry. View from public roads and riverbanks only. |
References
- National Database of Cultural Properties, Agency for Cultural Affairs: Okutsu Power Station Yoshii River Water Intake Weir
- https://kunishitei.bunka.go.jp/heritage/detail/101/00005904
- 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