What Is the Yokoyu River No. 50 Dam?
The Yokoyu River No. 50 Dam (横湯川第五〇号堰堤, Yokoyugawa Dai-gojūgō Entei) is a gravity-type concrete erosion-control dam built in 1925 beside the Wago Bridge in the center of Shibu Onsen, Yamanouchi Town, Nagano Prefecture, and registered as a Registered Tangible Cultural Property of Japan on October 14, 2021. It is 34 meters long and 2.4 meters high, and Nagano Prefecture owns it.
It lies about 160 meters above No. 39, seventh from the bottom of the series. A product of the Home Ministry's direct works, it is the shortest of the eight dams.
A Narrow Spillway between Squared Shoulders
Of all eight, the Yokoyu River No. 50 Dam has the clearest shape. The Agency for Cultural Affairs picks out two features: a narrowed spillway notch and shoulders built steeply in squared stone using Sangi-zumi corners.
The spillway notch is the lowered section of the crest that carries the water over. On No. 50 it has been pinched in, gathering the flow into the middle of the dam before it drops. On either side, the shoulders rise high in dressed stone. Sangi-zumi is the corner technique familiar from Japanese castle walls, in which long rectangular blocks are laid with their long and short faces alternating, giving a straight, sharp arris.
Next to the dams faced with fieldstone or river cobbles, the stone here is visibly more worked. Short as it is, the Yokoyu River No. 50 Dam has the most precise outline of any structure in the river.
Part of the Wago Bridge Scene
The Wago Bridge crosses the Yokoyu at the heart of Shibu Onsen, with inns and houses gathered around it. The agency says the Yokoyu River No. 50 Dam and the bridge together create a modern river landscape.
Bridge and dam stand close together and anchor the view of the river in the middle of town. Of the eight, this is the dam that most directly embodies the registration criterion of contributing to the historic landscape of the country. Its registration number is 20-0597.
Seeing the Yokoyu River No. 50 Dam
Sitting beside the Wago Bridge, the Yokoyu River No. 50 Dam is the easiest of the Yokoyu River Stone Masonry Dams to find. It is an outdoor structure with no admission fee, seen from the bridge and nearby roads. The official photographs show the front from the right bank and the back from the left bank. The sangi-zumi shoulders read best from a slight angle to the front, where the stacked edges line up. Cars use the bridge, so take care if you stop. There is no signposted route to the riverbed; keep away from the water when it is high. Directions to the Wago Bridge are on the Yokoyu River Stone Masonry Dams page.
- 📍 Plan Your Visit to Nagano
- Find tours, activities & transport passes near Yokoyu River No. 50 Dam
- [ Matsumoto Castle & Kamikochi Hiking Tours ]
Q&A
- Where is the Yokoyu River No. 50 Dam?
- In the Yokoyu River beside the Wago Bridge, in the center of Shibu Onsen in Yamanouchi, Nagano.
- When was the Yokoyu River No. 50 Dam built?
- In 1925, as part of the Home Ministry's direct erosion-control works.
- What are the main features of the Yokoyu River No. 50 Dam?
- A narrowed spillway notch flanked by shoulders built steeply in squared stone with sangi-zumi corners. It is 34 meters long and 2.4 meters high.
- Why is the Yokoyu River No. 50 Dam a Registered Tangible Cultural Property?
- Together with the Wago Bridge it forms a modern river landscape at the center of the hot spring town, and it was registered on October 14, 2021, for its contribution to the historic landscape.
- Can I visit the Yokoyu River No. 50 Dam?
- Yes. You can see it from the Wago Bridge and nearby roads at no charge. Keep away from the river when the water is high.
Basic Information
| Name | Yokoyu River No. 50 Dam (Yokoyugawa Dai-gojūgō Entei) |
|---|---|
| Location | Yokoyu to Miyamae, Hirao, Yamanouchi Town, Shimotakai District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2021 (registered) |
| Quantity | 1 dam |
| Dimensions | Crest length 34 m, height 2.4 m (gravity-type concrete, squared-stone sangi-zumi shoulders) |
| Owner | Nagano Prefecture |
| Public Access | Outdoor erosion-control structure; viewable from the Wago Bridge and nearby roads (no admission fee) |
References
- Database of National Cultural Properties (Agency for Cultural Affairs): Yokoyu River No. 50 Dam
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00014010
- Cultural Heritage Online: Yokoyu River No. 50 Dam (Japanese)
- https://online.bunka.go.jp/heritages/detail/592010
- 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
