What Is the Yokoyu River No. 2 Dam?
The Yokoyu River No. 2 Dam (横湯川第二号堰堤, Yokoyugawa Dai-nigō Entei) is a gravity-type concrete erosion-control dam built in 1937 on the Yokoyu River in Yamanouchi Town, Nagano Prefecture, and registered as a Registered Tangible Cultural Property of Japan on October 14, 2021. It measures 45 meters long and 3.0 meters high and is owned by Nagano Prefecture.
It sits about 200 meters above No. 1, making it the second dam from the bottom of the series. It dates from the period after 1932, when the project passed from the national government to the prefecture.
Rounded Cobbles, Carefully Matched
The thing to look at on the Yokoyu River No. 2 Dam is the stone. According to the Agency for Cultural Affairs, the face was built up with care from river cobbles of uniform size. These are stones the river itself has rounded, and here they have been sorted and set in tidy rows.
Compare it with No. 51 upstream, faced with irregular fieldstone, or No. 50, whose squared corner stones stand crisp and sharp, and the difference is obvious. The even rows of round stones make a fine, regular pattern across the face.
At 3.0 meters it is very low for its 45-meter length. The agency's description singles out this restrained height and notes that the dam fits naturally into the mountain scenery. Built low and from the same kind of stone that lines the riverbed, it does not stand out against the valley.
Part of a Channel-Works Scheme
The agency's description says the Yokoyu River No. 2 Dam forms part of a channel works. Channel works (流路工, ryūrokō) do not rely on one large dam to stop sediment. Instead, a sequence of low weirs and protected banks shapes the river's course so that the flow stays steady.
Nagano Prefecture's records say the prefectural works that began in 1932 followed a plan by the engineer Akagi Masao, who designed channel works for the Yokoyu and Kakuma rivers and supervised their construction. Seen in that light, the low profile of the Yokoyu River No. 2 Dam makes sense: it is one step among many, not a barrier on its own.
Why the Yokoyu River No. 2 Dam Was Registered
The Yokoyu River No. 2 Dam (registration number 20-0592) was registered for its contribution to the historic landscape of the country. Its even cobble facing and its low, unobtrusive form preserve the look of a modern erosion-control work in good condition.
Seeing the Yokoyu River No. 2 Dam
The Yokoyu River No. 2 Dam is an outdoor structure with no admission fee, seen from the roads and bridges along the river. The official photographs show the front from the right bank and the back from the left bank. To pick out the rows of cobbles, come in the morning or late afternoon, when low light throws a shadow under each rounded stone. No. 1 and No. 3 are each about 200 meters away. There is no signposted way down to the riverbed, so keep clear of 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. 2 Dam
- [ Matsumoto Castle & Kamikochi Hiking Tours ]
Q&A
- When was the Yokoyu River No. 2 Dam built?
- In 1937, during the period after Nagano Prefecture took over the project from the national government.
- What kind of stone faces the Yokoyu River No. 2 Dam?
- River cobbles of uniform size, rounded by the water and laid carefully in even rows.
- How big is the Yokoyu River No. 2 Dam?
- It is 45 meters long and 3.0 meters high, kept deliberately low for its length.
- What does "channel works" mean for the Yokoyu River No. 2 Dam?
- Channel works stabilize a river with a series of low weirs and protected banks rather than one large dam. The Agency for Cultural Affairs describes the Yokoyu River No. 2 Dam as part of such a scheme.
- Can I visit the Yokoyu River No. 2 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. 2 Dam (Yokoyugawa Dai-nigō Entei) |
|---|---|
| Location | Andai to Kurokawa, Hirao, Yamanouchi Town, Shimotakai District, Nagano Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2021 (registered) |
| Quantity | 1 dam |
| Dimensions | Crest length 45 m, height 3.0 m (gravity-type concrete, faced with river cobbles) |
| 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. 2 Dam
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00014005
- Cultural Heritage Online: Yokoyu River No. 2 Dam (Japanese)
- https://online.bunka.go.jp/heritages/detail/553885
- Nagano Prefecture Hokushin Construction Office: Design Guidance by Dr. Akagi Masao (PDF, Japanese)
- https://www.pref.nagano.lg.jp/hokuken/documents/akagihakase_sekkei_japanese.pdf
Last verified: 2026.10.01
