What Is the Yokoyu River No. 39 Dam?
The Yokoyu River No. 39 Dam (横湯川第三九号堰堤, Yokoyugawa Dai-sanjūkyūgō Entei) is a gravity-type concrete erosion-control dam built in 1924 on the Yokoyu River where it runs through Shibu Onsen in Yamanouchi Town, Nagano Prefecture, and registered as a Registered Tangible Cultural Property of Japan on October 14, 2021. It is 41 meters long and 3.6 meters high and is owned by Nagano Prefecture.
It is the oldest of the eight registered dams, an early product of the Home Ministry's direct works that began in 1918. It stands about 120 meters upstream of the 1944 Yokoyu River Dam.
A Dam Built in Two Tiers
The first thing to notice about the Yokoyu River No. 39 Dam is that it has two tiers. According to the Agency for Cultural Affairs, a second, lower wall was built onto the downstream face of the 3.6-meter main body as a single structure. Water spilling over the top lands on the lower step and then falls a second time.
Sabo engineers often place a separate small weir some distance below a main dam, known as a sub-dam. Here the lower step is fused to the main body instead. Splitting the drop in two softens the impact of the falling water and makes it harder for the river to scour out the bed just below the dam.
Built Heavier than the Rest
The agency describes the Yokoyu River No. 39 Dam as particularly sturdy, even within a group of dams all designed to stop turbulence on a steep gradient and hold back sediment. Its 3.6-meter height is second only to the 3.8-meter Yokoyu River Dam among the eight, and the two-tier form comes on top of that.
The river runs steep and unsettled along this stretch. That the Home Ministry put a tall, two-step dam here so early in its program says something about how hard the water pushes at this point. Roughly a century on, the Yokoyu River No. 39 Dam is still in service as an erosion-control structure.
Why the Yokoyu River No. 39 Dam Was Registered
The Yokoyu River No. 39 Dam (registration number 20-0596) was registered for its contribution to the historic landscape of the country. It is the oldest dam in the series, and it keeps a two-tier form found on none of the others essentially as it was built in 1924.
Seeing the Yokoyu River No. 39 Dam
The Yokoyu River No. 39 Dam is an outdoor structure with no admission fee, seen from the roads and bridges nearby. Both official photographs, front and back, were taken from the right bank. The two tiers are easiest to read from an angle on the downstream side, where the steps overlap. No. 50, beside the Wago Bridge, is about 160 meters upstream. 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. 39 Dam
- [ Matsumoto Castle & Kamikochi Hiking Tours ]
Q&A
- When was the Yokoyu River No. 39 Dam built?
- In 1924, by the Home Ministry. It is the oldest of the eight registered Yokoyu River dams.
- How big is the Yokoyu River No. 39 Dam?
- It is 41 meters long and 3.6 meters high.
- What is unusual about the Yokoyu River No. 39 Dam?
- It is built in two tiers: a lower wall is joined to the downstream face of the main body, so the falling water is checked twice.
- Why was the Yokoyu River No. 39 Dam built so sturdily?
- It sits on a steep, turbulent stretch, and its job is to calm the flow and hold back sediment. The Agency for Cultural Affairs singles it out as particularly robust.
- Can I visit the Yokoyu River No. 39 Dam?
- Yes. It can be seen from the roads and bridges nearby at no charge. Keep away from the river when the water is high.
Basic Information
| Name | Yokoyu River No. 39 Dam (Yokoyugawa Dai-sanjūkyūgō Entei) |
|---|---|
| Location | Shibuyu to Muranishi, Hirao, Yamanouchi Town, Shimotakai District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2021 (registered) |
| Quantity | 1 dam |
| Dimensions | Crest length 41 m, height 3.6 m (gravity-type concrete, two-tier body) |
| 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. 39 Dam
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00014009
- Cultural Heritage Online: Yokoyu River No. 39 Dam (Japanese)
- https://online.bunka.go.jp/heritages/detail/598279
- 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
