The Largest and Highest Dam
The Ashizawa No. 4 Stone Masonry Dam (芦澤第四号石積堰堤, Ashizawa dai-yongō 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 20-0458, and the dam belongs to Nagano Prefecture.
It is the uppermost of the four Meiji-era stone dams on the stream, 300 metres above No. 3, and its registered site extends beyond the Ashizawa land parcel into neighbouring ground.
The Ashizawa No. 4 Stone Masonry Dam is 15 metres long at the crest and 6.8 metres high, which the Agency for Cultural Affairs identifies as the largest of the four. Nagano Prefecture's Saigawa Sabo Office gives the length as 15.3 metres. The other three are held to around 4 metres in height; only No. 4 reaches 6.8 metres.
Why It Was Registered
The dam was registered for contributing to the historic landscape of the country. The Agency's note points to its size and to its andesite stone, shared with the other three dams, and calls it a valuable survival from the very first public works carried out by the Home Ministry after its regional civil engineering supervisory offices were established.
The Ashizawa works appear in a 1911 Home Ministry record of mountain sabo projects, which dates them to April through December 1887. Ashizawa No. 4 shows in concrete form what a national campaign to control erosion in the Shinano River headwaters left behind in one small mountain valley.
The masonry follows the same method as its companions: fieldstones about 50 to 120 centimetres across, laid without mortar in the mutsumaki dry-stone technique. Holding a face 6.8 metres high together by the fit of the stones alone is what makes this dam the technical high point of the set.
What to Look For
Take in the height first. The three dams below are low enough to look across or even down on; at the Ashizawa No. 4 Stone Masonry Dam you look up. The stone face rises to roughly 4 times the height of a person, spanning the stream.
Move closer and watch how large rounded boulders and smaller stones alternate and lock together, with the joints holding firm even as the wall climbs. The straight-edged division between the central spillway and the wings is the same as on the other three, and on a dam this size it reads clearly from a distance.
No. 4 stands at the most secluded point of the walk, in a wooded stretch of the valley that has been laid out so visitors can see the dam at close range.
Visiting No. 4
The Ashizawa No. 4 Stone Masonry Dam is an open-air structure with no fee and no booking. It marks the end of the streamside path, about 5 minutes' walk upstream beyond the reinforced concrete sabo dam above No. 3, according to the Saigawa Sabo Office's 2021 directions. A prefectural blog puts the round trip from the Omi Village sports ground car park to No. 4 at about 1 hour.
In the upper section, 3 ageing wooden footbridges were replaced in fiscal 2023, and the path was surfaced with gravel in fiscal 2025. Nagano Prefecture still warns of uneven footing and falling stones and branches, so wear sturdy shoes.
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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Q&A
- When was the Ashizawa No. 4 Stone Masonry Dam built and registered?
- It was built in 1887 as part of a Home Ministry sabo project and registered as a Registered Tangible Cultural Property on October 7, 2014, under registration number 20-0458.
- How big is the Ashizawa No. 4 Stone Masonry Dam?
- The Agency for Cultural Affairs records it as 15 metres long and 6.8 metres high, the largest of the four Ashizawa dams. The Saigawa Sabo Office gives the length as 15.3 metres.
- Why is the Ashizawa No. 4 Stone Masonry Dam considered valuable?
- The Agency for Cultural Affairs calls it a valuable survival from the earliest public works carried out by the Home Ministry after its civil engineering supervisory offices were set up.
- How far do I have to walk to reach the Ashizawa No. 4 Stone Masonry Dam?
- It is at the top of the streamside path. A Nagano Prefecture blog puts the round trip from the Omi Village sports ground car park at about 1 hour. There is no fee or booking.
- What should I watch out for when visiting the Ashizawa No. 4 Stone Masonry Dam?
- Nagano Prefecture warns of uneven footing and falling stones and branches. Wear sturdy shoes and view the dam from the path rather than climbing onto it.
Basic Information
| Name | Ashizawa No. 4 Stone Masonry Dam (芦澤第四号石積堰堤) |
|---|---|
| Location | Aza Ashizawa and other areas, Asa, Omi Village, Higashichikuma District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | Registered 2014/10/7 (Heisei 26), registration no. 20-0458 |
| Quantity | 1 structure |
| Dimensions | Crest length 15 metres, height 6.8 metres |
| Owner | Nagano Prefecture |
| Public Access | Open-air sabo structure; free access; recommended season spring to autumn (Nagano Prefecture sabo division) |
References
- 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 No. 4 Stone Masonry Dam (Cultural Heritage Online)
- https://online.bunka.go.jp/heritages/detail/234261
- 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 stone masonry dams, Omi Village (Nagano Prefecture Saigawa Sabo Office)
- https://www.pref.nagano.lg.jp/saisabo/jigyo/ashizawa201403.html
- 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
- Sai Sabo Dayori, July 2021 (Nagano Prefecture Saigawa Sabo Office)
- https://www.pref.nagano.lg.jp/saisabo/jigyo/documents/saisabodayorir3-2-1.pdf
- Modern heritage card No. 2: Ashizawa stone masonry dams (Nagano Prefecture blog, Matsumoto region)
- https://blog.nagano-ken.jp/matsuchi/recommend/viewspots/39197.html
Last verified: 2026.10.06
