An Edo-Period Dam in a Side Valley
Uchihiro Sunadome (内広砂留, also written Uchihiro-sunadome), a dry-stone check dam in Nishinakajō, Kannabe-chō, Fukuyama City, Hiroshima Prefecture, was built in the late Edo period and registered as a Registered Tangible Cultural Property of Japan on 3 August 2006.
A sunadome is a sand-retaining dam. The word is older than the modern engineering term sabō, and in the Bingo region it refers specifically to the stone barriers that the Fukuyama domain threw across its eroding mountain streams. They are not reservoirs. Water passes through and over them freely; what they hold back is the granite grit that the hillsides shed after every heavy rain.
Uchihiro stands 3.8 metres high and runs 21 metres across. By the standards of the Dōdōgawa system it is modest. The sixth dam downstream from it, Dōdōgawa Rokuban Sunadome, is 13 metres high and 56 metres long and is often described as the largest stone check dam in Japan. Uchihiro sits above that giant, on a tributary entering the Dōdō River from the right bank, in a narrow side valley that carries the place name Tōtō-dani.
The Agency for Cultural Affairs registered eight of the Dōdōgawa dams together in 2006. Six carry numbers along the main stream. Two, Uchihiro and Tobigasako, guard the tributaries. Around fifty stone dams survive along the four kilometres of the valley in total, and roughly fifteen are still doing structural work.
Reading the Stonework
The registration criterion applied here covers structures contributing to the historic character of the landscape, but the technical interest is what makes Uchihiro worth the climb.
Everything is dry-laid. No mortar, no concrete core, nothing binding the granite blocks except their own weight and the friction of their faces. Engineers call this a gravity dam, and it is a fair description: the structure resists the push of accumulated sand by being heavy and by being shaped so that the load presses the stones together rather than apart.
Three distinct masonry techniques appear in one small structure, which is unusual and is why specialists come here.
The wing walls on either side use ranzumi, random coursing, in which stones of differing sizes are fitted where they best fit rather than laid in level beds. Look along a wing and no continuous horizontal joint runs through it. The corners use sangizumi, the technique in which long and short faces alternate as they rise, interlocking at right angles the way the ends of a log cabin do. Japanese castle builders used the same method on the angles of their stone bases, and for the same reason: corners fail first.
The upper portion is built in tanizumi, laid in stepped tiers with the stones set on the diagonal so that each presents a point downward. Rainwater running over a diagonal face sheds sideways instead of driving straight into a horizontal joint.
One more detail repays attention. The wing walls project forward from the spillway notch rather than sitting flush with it. Water leaving the notch is thrown clear of the stonework at the sides, which is precisely where an unprotected dry-stone wall would be undercut. Nobody wrote this down as a design principle in the eighteenth century; it was learned by watching dams fail.
The dating reflects that long process. The Agency for Cultural Affairs assigns the original construction to the late Edo period, somewhere in the span between 1751 and 1829, with additional building in the Meiji era between 1868 and 1911. Almost every dam in the valley shows the same pattern of repair and heightening. They were maintained because they were needed, not because anyone considered them historic.
Visiting the Valley
The whole Dōdōgawa system is open ground, freely accessible at any hour, with no admission charge and no restriction on photography. It is also, in the upper reaches, genuinely rough country.
Dōdō Park is the sensible base. The park occupies the sediment flat impounded behind Rokuban Sunadome, laid out with clipped shrubs, mature trees and a stone-lined watercourse running some 344 metres, and it is the one part of the valley with car parking, level paths and signposting. Reach it by car in about 20 minutes from the Fukuyama-Higashi interchange on the Sanyō Expressway, or roughly 15 minutes by taxi from Kannabe Station on the JR Fukuen Line. Public transport beyond that point is thin.
Walk up from the park and Rokuban rises in front of you, a stepped granite wall on a slope of about one in ten. Most visitors stop here, and it is a fine place to stop.
Continuing to Uchihiro means leaving the main stream for the right-bank tributary above Rokuban and following a much narrower path. Footing is uneven, the route is not consistently marked, and after rain the stream bed is slippery. Boots rather than trainers. Going alone is not advisable, and the local volunteer group Dōdōgawa Hotaru Dōkōkai, which maintains the valley, can be a useful first contact for anyone wanting to see the upper dams properly.
Two seasons stand out. Fireflies appear along the stream in June, the result of years of habitat work by that same volunteer group. In late September the banks turn red with cluster amaryllis, and white and yellow varieties grow here as well. Summer brings families to the shallow water below the park; the upper valley stays quiet year-round.
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Q&A
- What exactly is Uchihiro Sunadome, and how does it differ from a normal dam?
- It is a check dam built to trap sediment rather than store water. Water flows through and over it; the granite grit washing off the hillsides is what it holds. It is 3.8 metres high and 21 metres long, built of dry-laid granite with no mortar, and it still functions as part of Fukuyama's erosion control system.
- Can Uchihiro Sunadome be visited, and is there an admission fee?
- The site is open country with no gate, no opening hours and no charge, and photography is unrestricted. Reaching it requires walking up a rough tributary path above Rokuban Sunadome, which is not consistently signposted. Sturdy footwear is needed, and going after heavy rain is unwise.
- How do I get to the Dōdōgawa sunadome area where Uchihiro Sunadome stands?
- Dōdō Park is the access point. It is about 20 minutes by car from the Fukuyama-Higashi interchange on the Sanyō Expressway, or about 15 minutes by taxi from Kannabe Station on the JR Fukuen Line. Parking at the park is free. Buses do not run close to the upper valley.
- When was Uchihiro Sunadome built, and who built it?
- The Agency for Cultural Affairs dates the original structure to the late Edo period, within the range 1751 to 1829, with Meiji-era additions between 1868 and 1911. The Dōdōgawa dams were built under the Bingo-Fukuyama domain, which faced repeated sediment disasters from the weathered granite slopes above Kannabe.
- What is the best time of year to see Uchihiro Sunadome and the Dōdō valley?
- June for fireflies along the stream and late September for cluster amaryllis on the banks. Winter gives the clearest view of the stonework itself, since fallen leaves and low vegetation expose the courses. Avoid the days immediately after heavy rain.
Basic Information
| Name | Uchihiro Sunadome / 内広砂留 |
|---|---|
| Location | Tōtō-dani, Nishinakajō, Kannabe-chō, Fukuyama City, Hiroshima Prefecture |
| Designation | Registered Tangible Cultural Property (Structure), registration number 34-0082 |
| Year Designated | Registered 3 August 2006 (gazetted 24 August 2006) |
| Quantity | 1 structure |
| Dimensions | Gravity-type stone check dam; 21 m long, 3.8 m high |
| Owner | The State (Ministry of Land, Infrastructure, Transport and Tourism) |
| Public Access | Open land, accessible at all times without charge; upper valley paths are unimproved |
References
- National Designated Cultural Properties Database, Agency for Cultural Affairs — Uchihiro Sunadome
- https://kunishitei.bunka.go.jp/heritage/detail/101/00005667
- Cultural Heritage Online — Uchihiro Sunadome
- https://bunka.nii.ac.jp/heritages/detail/152275
- Fukuyama City — Index of Designated and Registered Cultural Properties
- https://www.city.fukuyama.hiroshima.jp/soshiki/bunka/63787.html
- Fukuyama City — Fukuyama Cultural Properties Map
- https://www.city.fukuyama.hiroshima.jp/soshiki/bunka/179333.html
- Dive! Hiroshima, Hiroshima Prefecture Tourism Association — The Dōdōgawa Sunadome and Dōdō Park
- https://dive-hiroshima.com/explore/1622/
Last verified: 2026.08.08