What Is the Yokoyu River No. 57 Dam?
The Yokoyu River No. 57 Dam (横湯川第五七号堰堤, Yokoyugawa Dai-gojūnanagō Entei) is a gravity-type concrete erosion-control dam built in 1927 on the Yokoyu River just above Shibu Onsen in Yamanouchi Town, Nagano Prefecture, and registered as a Registered Tangible Cultural Property of Japan on October 14, 2021. It is 58 meters long and 2.0 meters high, and it belongs to Nagano Prefecture.
It sits about 230 meters above No. 50, the furthest upstream of the eight registered dams. At 58 meters it is also the longest.
A Gentle Upstream Face and a Steep Downstream One
The Yokoyu River No. 57 Dam is unusual in that the Agency for Cultural Affairs records the slopes of its faces. The upstream face has a batter of 5 bu and the downstream face 3 bu. In the traditional Japanese notation, 5 bu means 0.5 units of horizontal run for every unit of height, and 3 bu means 0.3.
So the upstream side leans back gently while the downstream side stands nearly upright. On a 2.0-meter dam, that puts the toe of the upstream face about 1 meter out from the crest, and the downstream toe only about 60 centimeters. Keeping the downstream face steep is standard sabo practice, since that is the face struck and worn by gravel coming over the top, and No. 57 follows it.
The faces are built in natural stone, so the longest wall of the eight crosses the river as one continuous band of fieldstone.
Flood Control for the Whole Shinano River System
The Yokoyu flows into the Yomase River, then the Chikuma, which becomes the Shinano in Niigata Prefecture and reaches the Sea of Japan. The agency describes the Yokoyu River No. 57 Dam as part of the Home Ministry's flood-control program for the Shinano River system. Sediment pouring out of the eroding valley above affects not only the Yokoyu but the big rivers below it, so this small mountain dam was one piece of a much larger scheme.
The agency also notes that the dam still performs its protective role today. Since its completion in 1927 it has been catching sediment at the top of the series.
Why the Yokoyu River No. 57 Dam Was Registered
The Yokoyu River No. 57 Dam (registration number 20-0598) was registered for its contribution to the historic landscape of the country. It keeps the form of the Home Ministry's direct works and has served as a working flood-control structure from completion to the present.
Seeing the Yokoyu River No. 57 Dam
The Yokoyu River No. 57 Dam is a little over 200 meters upstream of the Wago Bridge. It is an outdoor structure with no admission fee, seen from the roads and bridges nearby. The official photographs show the front from the right bank and the back from upstream; it is the only one of the eight whose back was photographed from the upstream side. There is no signposted route to the riverbed; keep away from the water when it is high. Directions to Shibu Onsen are on the Yokoyu River Stone Masonry Dams page.
- 📍 Plan Your Visit to Nagano
- Find tours, activities & transport passes near Yokoyu River No. 57 Dam
- [ Matsumoto Castle & Kamikochi Hiking Tours ]
Q&A
- When was the Yokoyu River No. 57 Dam built?
- In 1927, by the Home Ministry.
- Where is the Yokoyu River No. 57 Dam?
- On the Yokoyu River in Shibu Onsen, Yamanouchi, a little over 200 meters upstream of the Wago Bridge. It is the uppermost of the eight registered dams.
- How big is the Yokoyu River No. 57 Dam?
- It is 58 meters long and 2.0 meters high, the longest of the eight.
- What are the face slopes of the Yokoyu River No. 57 Dam?
- The upstream face is 5 bu (0.5 horizontal to 1 vertical) and the downstream face 3 bu (0.3 to 1), so the downstream side is the steeper.
- Is the Yokoyu River No. 57 Dam still in use?
- Yes. The Agency for Cultural Affairs notes that it still performs its protective role. You can see it from the roads and bridges nearby at no charge.
Basic Information
| Name | Yokoyu River No. 57 Dam (Yokoyugawa Dai-gojūnanagō Entei) |
|---|---|
| Location | Yokoyu to Tenkawa, Hirao, Yamanouchi Town, Shimotakai District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2021 (registered) |
| Quantity | 1 dam |
| Dimensions | Crest length 58 m, height 2.0 m (gravity-type concrete; upstream batter 5 bu, downstream 3 bu) |
| Owner | Nagano Prefecture |
| Public Access | Outdoor erosion-control structure; viewable from roads and bridges (no admission fee) |
References
- Database of National Cultural Properties (Agency for Cultural Affairs): Yokoyu River No. 57 Dam
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00014011
- Cultural Heritage Online: Yokoyu River No. 57 Dam (Japanese)
- https://online.bunka.go.jp/heritages/detail/544551
- Nagano Prefecture: Overview of Erosion Control by River System (PDF, Japanese)
- https://www.pref.nagano.lg.jp/sabo/siryou/documents/04_4suikeisabo.pdf
Last verified: 2026.10.01
