An Intake That Survives Complete
What makes the Kirotani-gawa Intake Weir (Kirotanigawa Shusui Entei) unusual within the Okutsu Power Station group is how much of it remains. This is not just a weir but a whole intake ensemble: a gravity weir of mortared stone about 12 metres long and 2.7 metres high, a reinforced-concrete sediment-flushing gate on the right bank, stone revetment protecting the banks, and a single-arched intake opening through which water enters the canal. The parts that let a stream be tapped for power all stand together, in good condition, as one working unit.
The weir is built across the Kirotani-gawa, a right-bank tributary of the Yoshii River, and it feeds a branch canal that joins the main headrace of the Okutsu scheme just west of the plant's No. 1 Covered Conduit. The same small stream is crossed elsewhere by the No. 1 Aqueduct, so the Kirotani-gawa appears twice in this system, once as an obstacle to be bridged and once as a source to be drawn from. The weir dates to 1932 and was built by Chugoku Godo Denki, the utility behind the whole plant.
Why Completeness Counts
The intake was registered as a Tangible Cultural Property in October 2006 under No. 33-0118, one of the many Okutsu components listed together under the criterion of contributing to the historic character of the national landscape. Among the group's several intake weirs, this one is valued for its integrity. When a structure keeps its sediment gate, its revetment and its arched intake all in place, it lets a visitor read the full sequence of how water was captured, cleaned of debris, and admitted into the canal.
Each element has a job. The mortared-stone gravity weir holds back and raises the water; the reinforced-concrete flush gate on the right bank clears out gravel so the intake stays open; the stone revetment guards the banks against scour; and the single-arch opening is the doorway through which the diverted water begins its journey to the powerhouse. Seeing them in one place is a compact lesson in early-Showa waterworks, which is exactly the historic value the registration recognises.
What to Watch for on the Ground
Approach the weir and let your eye move through the sequence: the stone crest with water spilling over it, the arched mouth of the intake to one side, and the concrete gate that can be opened to sluice sediment away. The arch is the detail to linger on, a small, deliberate piece of masonry framing the point where the stream is turned to human use. The mix of hand-set stone and cast concrete tells you this is a structure from the moment when the two building traditions overlapped.
The Kirotani-gawa runs through forested slopes in the upper Yoshii valley, in the Kamisaihara district of Kagamino, north of the Okutsu Onsen hot springs. As with the rest of the scheme, there is no visitor car park or interpretive board here, and the intake stands on land tied to a working power plant. View it from public ground, treat it as live equipment, and appreciate it alongside the other Okutsu structures rather than in isolation.
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Q&A
- What makes this intake worth noting among the others?
- The whole intake apparatus survives together, the weir, the sediment gate, the revetment and the arched intake, in good condition. That completeness lets you read the full process of diverting a stream into the canal.
- What is the arched opening?
- It is the single-arch intake, the mouth through which water drawn from the Kirotani-gawa enters the branch canal on its way to join the main headrace.
- How big is the weir, and when was it built?
- It is about 12 metres long and 2.7 metres high, a mortared-stone gravity weir with a reinforced-concrete flush gate, built in 1932 and registered under No. 33-0118 in 2006.
- Is this the same stream the No. 1 Aqueduct crosses?
- Yes. The Kirotani-gawa is both bridged by the No. 1 Aqueduct and tapped by this weir, so the same tributary serves the system in two different ways.
- Can visitors get close to it?
- It sits on operational land with no visitor facilities and should be viewed from public ground, as part of the wider Okutsu group along the valley.
Basic Information
| Name | Okutsu Power Station Kirotani-gawa Intake Weir (Okutsu Hatsudensho Kirotanigawa Shusui Entei) |
|---|---|
| Location | Kamisaihara, Kagamino, Tomata District, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure), No. 33-0118 |
| Registered | 18 October 2006 |
| Built | 1932 (Showa 7) |
| Quantity / Scale | 1 structure; gravity concrete weir, length approx. 12 m, height approx. 2.7 m, with sediment gate and revetment |
| Owner | The Chugoku Electric Power Co., Inc. |
| Access | Working infrastructure; no public entry. View from public ground only. |
References
- National Database of Cultural Properties (ACA) — Okutsu Power Station Kirotani-gawa Intake Weir
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00005908
- Cultural Heritage Online — Okutsu Power Station Kirotani-gawa Intake Weir
- https://bunka.nii.ac.jp/heritages/detail/185813
- Chugoku Electric Power — Hydroelectric Stations
- https://www.energia.co.jp/energy/general/water/water_all.html
- Kagamino Town official site
- https://www.town.kagamino.lg.jp/
Last verified: 2026.07.04