Three Spans Carrying a Trough of Water
Further along the headrace of the Okutsu Power Station, where the canal meets the Yu-no-tani-gawa, the water crosses on the No. 3 Aqueduct (Sango Suirokyo). Unlike the plant's single-span No. 1 Aqueduct upstream, this one is a three-span reinforced-concrete rigid-frame bridge, its length of about 18 metres broken into bays of roughly 6.1 metres each. It carries not a road but a concrete flume, a channel with a nearly trapezoidal cross-section that measures about 3.0 metres across the top and 2.7 metres at the bottom.
The Yu-no-tani-gawa is another right-bank tributary of the Yoshii River, and the aqueduct sits roughly 690 metres downstream of the plant's No. 1 Covered Conduit. By this point the canal has already crossed one stream, run through a long covered channel, and gathered water from side intakes; the No. 3 Aqueduct is the next step in that steady progress toward the powerhouse. It was built in 1932 by Chugoku Godo Denki as part of the same scheme.
A Variation on a Repeated Problem
The bridge was registered as a Tangible Cultural Property in October 2006 under No. 33-0120, listed together with the other Okutsu structures for contributing to the historic character of the national landscape. Seen beside the No. 1 Aqueduct, it shows how the same engineers solved the same basic problem, carrying water over a stream, in more than one way. Where the first crossing used a single span, the wider or more awkward gap here called for three, joined into one continuous rigid frame.
That repetition with variation is part of what gives the Okutsu group its value. A designer crossing several streams in succession does not simply copy one bridge; the span count and proportions are tuned to each site. The trapezoidal flume, wider at the top than the bottom, is shaped to carry the required volume of water while keeping the structure as light as the reinforced concrete of the day allowed. The result is a family of related crossings, each slightly different, strung along a single canal.
Seeing It in Sequence
The No. 3 Aqueduct is best understood as one stop on a walk that follows the water. Trace the canal from the intake weirs, through the covered conduit, past the earlier crossing, and you arrive here, at a three-bay frame lifting the flume over the Yu-no-tani-gawa. Look at the underside: the rhythm of three openings and the shape of the trough overhead read clearly from the streambed. The trapezoidal section is subtle but visible once you know to look for the narrowing toward the base.
This is forested country in the upper Yoshii valley, part of the Kamisaihara district of Kagamino, upstream of the Okutsu Onsen hot springs. The aqueduct has no visitor parking or signboard and belongs to a working power plant, often standing on operational land. As with every structure in the group, the way to appreciate it is from public ground, at a respectful distance, as one link in a continuous 1930s watercourse that still carries water today.
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Q&A
- How does the No. 3 Aqueduct differ from the No. 1?
- The No. 1 Aqueduct is a single span, while the No. 3 is a three-span rigid-frame bridge of similar overall length. They show the same engineers adapting one design to different stream crossings.
- What does it carry?
- It carries a concrete water channel, or flume, not a road. The flume has a nearly trapezoidal cross-section, about 3.0 metres wide at the top and 2.7 metres at the bottom.
- How big is it, and when was it built?
- It is about 18 metres long, divided into three spans of roughly 6.1 metres, built in 1932. It was registered under No. 33-0120 in 2006.
- Which stream does it cross?
- It crosses the Yu-no-tani-gawa, a right-bank tributary of the Yoshii River, about 690 metres downstream of the No. 1 Covered Conduit.
- Can I walk across it?
- No. It carries flowing water rather than a footway and stands on operational land. It should be viewed from public ground along with the rest of the Okutsu group.
Basic Information
| Name | Okutsu Power Station No. 3 Aqueduct (Okutsu Hatsudensho Sango Suirokyo) |
|---|---|
| Location | Kamisaihara, Kagamino, Tomata District, Okayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure), No. 33-0120 |
| Registered | 18 October 2006 |
| Built | 1932 (Showa 7) |
| Quantity / Scale | 1 structure; reinforced-concrete three-span rigid-frame bridge, length approx. 18 m (span approx. 6.1 m) |
| Owner | The Chugoku Electric Power Co., Inc. |
| Access | Working infrastructure; no public crossing. View from public ground only. |
References
- National Database of Cultural Properties (ACA) — Okutsu Power Station No. 3 Aqueduct
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00005910
- 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