The Long, Low Third Dam
The Ashizawa No. 3 Stone Masonry Dam (芦澤第三号石積堰堤, Ashizawa dai-sangō ishizumi entei) is a dry-laid stone sabo dam built in 1887 across the Ashizawa stream in Asa, Omi Village, Higashichikuma District, Nagano Prefecture, and it was entered on the national register as a Registered Tangible Cultural Property on October 7, 2014. Its registration number is 20-0457, and the dam belongs to Nagano Prefecture.
It is the third of the four Meiji-era stone dams counting from the bottom, 190 metres upstream of No. 2 and 300 metres below No. 4.
The Ashizawa No. 3 Stone Masonry Dam is 16 metres long at the crest and 4.0 metres high, the longest crest of the four. Nagano Prefecture's Saigawa Sabo Office gives the length as 15.8 metres. Its downstream face is laid back at a batter of 1 to 1.3, receding 1.3 units horizontally for every unit of height, so the stonework reads as a sloping bank rather than an upright wall.
Why It Was Registered
The dam was registered for contributing to the historic landscape of the country. The Agency for Cultural Affairs, in its note on No. 3, praises not size but strategy: low dams with gentle faces, set one after another along the stream, steadied the channel bed and helped vegetation return to the eroded slopes above. Ashizawa No. 3 is one link in that chain, and it is still doing the job it was built for.
The stones are undressed andesite and other fieldstones about 50 to 120 centimetres across, laid without mortar in the dry-stone technique known as mutsumaki, in which each boulder is wedged so the mass stands by itself. The Saigawa Sabo Office says the method took a high level of skill and would be hard to reproduce today. That a mortarless structure has stayed in service for more than 130 years is the heart of its value.
What to Look For
Standing below the Ashizawa No. 3 Stone Masonry Dam, follow the line of the crest first. The lower spillway in the middle and the raised wings on either side meet at crisp, straight breaks, so the outline stays sharp even though the dam is made of irregular boulders. This is the modern elevation the Agency describes.
Then look at the slope of the face. Laid back at 1 to 1.3, the boulders interlock as they climb at an angle, and at 4.0 metres the dam feels less like a wall to look up at than a ramp of stone stretched across the full width of the stream.
At 16 metres, the crest is noticeably longer than the 12 metres of No. 2 just downstream. Long, low and gently sloped, No. 3 is the clearest expression of the Ashizawa approach: calm the streambed with a series of modest barriers instead of catching everything behind one tall one.
Visiting No. 3
The Ashizawa No. 3 Stone Masonry Dam is an open-air structure with no fee and no booking. Walking up the streamside path, it is the third stone dam you reach, after No. 1 and No. 2. Nagano Prefecture lists no visiting conditions and recommends spring through autumn.
Between No. 3 and No. 4 stands a concrete sabo dam from the Showa era, rebuilt from fiscal 2019 into a barrier 4.65 metres high and 22.0 metres long. Its face is clad in local stone, and it sits where you can compare it directly with the Meiji dry-stone work.
View the dam from the path rather than climbing onto the face or into the spillway. The prefectural materials state no restrictions on photography. Directions to the valley, parking and the layout of the full walk are covered on the Ashizawa Stone Masonry Dams page.
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- Find tours, activities & transport passes near Ashizawa No. 3 Stone Masonry Dam
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Q&A
- When was the Ashizawa No. 3 Stone Masonry Dam built and registered?
- It was built in 1887 and registered as a Registered Tangible Cultural Property on October 7, 2014, under registration number 20-0457.
- How big is the Ashizawa No. 3 Stone Masonry Dam?
- The Agency for Cultural Affairs records it as 16 metres long and 4.0 metres high, with a downstream face laid back at a gentle batter of 1 to 1.3.
- Why is the Ashizawa No. 3 Stone Masonry Dam built so low?
- According to the Agency for Cultural Affairs, setting low, gently sloped stone dams one after another along the stream steadied the channel and helped vegetation return to the slopes.
- Do I need a reservation or ticket to see the Ashizawa No. 3 Stone Masonry Dam?
- No. It is an open-air sabo structure, Nagano Prefecture lists no visiting conditions, and spring to autumn is the recommended season. For safety, view it from the path.
- What is the newer dam just upstream of the Ashizawa No. 3 Stone Masonry Dam?
- It is a Showa-era concrete sabo dam between No. 3 and No. 4, rebuilt from fiscal 2019 into a barrier 4.65 metres high and 22.0 metres long and clad in local stone.
Basic Information
| Name | Ashizawa No. 3 Stone Masonry Dam (芦澤第三号石積堰堤) |
|---|---|
| Location | Aza Ashizawa, Asa, Omi Village, Higashichikuma District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | Registered 2014/10/7 (Heisei 26), registration no. 20-0457 |
| Quantity | 1 structure |
| Dimensions | Crest length 16 metres, height 4.0 metres |
| Owner | Nagano Prefecture |
| Public Access | Open-air sabo structure; free access; recommended season spring to autumn (Nagano Prefecture sabo division) |
References
- Ashizawa No. 3 Stone Masonry Dam (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00010147
- Ashizawa No. 3 Stone Masonry Dam (Cultural Heritage Online)
- https://online.bunka.go.jp/heritages/detail/281720
- Ashizawa No. 2 Stone Masonry Dam (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00010146
- Ashizawa No. 4 Stone Masonry Dam (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00010148
- Ashizawa stone masonry dams, Omi Village (Nagano Prefecture Saigawa Sabo Office)
- https://www.pref.nagano.lg.jp/saisabo/jigyo/ashizawa201403.html
- Sai Sabo Dayori, July 2021 (Nagano Prefecture Saigawa Sabo Office)
- https://www.pref.nagano.lg.jp/saisabo/jigyo/documents/saisabodayorir3-2-1.pdf
- Sabo planning for the conservation and use of historic stone masonry dams (Hokuriku Regional Development Bureau, MLIT)
- https://www.hrr.mlit.go.jp/library/happyoukai/R8/d/d-15.pdf
Last verified: 2026.10.06
