Japan's First Major Concrete Weir, 1922
The Okozu Diversion Weir (大河津分水洗堰) is a reinforced-concrete weir built in 1922 where the Okozu diversion channel leaves the Shinano River in Tsubame City, Niigata Prefecture, and was registered as a Registered Tangible Cultural Property (structure) on February 14, 2002 (Agency for Cultural Affairs). The Agency's reading is Ōkōzu Bunsui Senseki, while Tsubame City gives Ōkōzu Bunsui Araizeki.
The Agency for Cultural Affairs records a reinforced-concrete weir of 27 bays, 146 metres long, with a service bridge and 27 gates; registration number 15-0116, owned by the national government (Ministry of Land, Infrastructure, Transport and Tourism).
Protecting the Echigo Plain from Floods
According to the Agency for Cultural Affairs, the Okozu Diversion Weir was built with the flood channel about 60 kilometres from the mouth of the Shinano River to protect the Echigo Plain, regulating the flow passed down the main river.
Tsubame City explains that it was part of the national Shinano River improvement works begun in 1909 after the Yokotagire flood disaster, and was finished in the year water first ran through the diversion channel. In 2000 a new weir was built just upstream, and the old weir, after about 80 years of service, has been turned into a park.
Why It Was Registered
The Okozu Diversion Weir was registered as a structure that contributes to the historic landscape of the country. The Agency for Cultural Affairs calls it one of the representative remains of the Home Ministry's Shinano River works and Japan's first full-scale reinforced-concrete weir.
What to Look For
It is a large reinforced-concrete structure about 146 metres long, with 26 piers in a row, a service bridge and 27 gates (Agency for Cultural Affairs).
The Shinano River office of the Ministry of Land, Infrastructure, Transport and Tourism notes that the old weir lets visitors see Taisho-period civil engineering up close.
Visiting
Tsubame City and the ministry say that the area of the retired weir has been laid out as a park. No official information on opening hours has been found, so check before visiting.
The weir stands in Tsubame City at the fork of the Shinano River and the diversion channel (Agency for Cultural Affairs). Enquiries about cultural properties go to Tsubame City's culture promotion section (0256-63-7002) (Tsubame City).
Q&A
- When was the Okozu Diversion Weir built?
- In 1922 (Agency for Cultural Affairs).
- How is 大河津分水洗堰 read?
- The Agency gives Ōkōzu Bunsui Senseki; Tsubame City gives Ōkōzu Bunsui Araizeki.
- What was it for?
- To protect the Echigo Plain from floods by regulating the flow down the main Shinano River (Agency for Cultural Affairs).
- Why is it important?
- It is considered Japan's first full-scale reinforced-concrete weir (Agency for Cultural Affairs).
- When was it registered?
- On February 14, 2002.
Basic Information
| Name | Okozu Diversion Weir (大河津分水洗堰) |
|---|---|
| Location | Tsubame City, Niigata Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | Registered 2002/02/14 (Heisei 14) |
| Quantity | 1 structure |
| Dimensions | Reinforced concrete, 27 bays, 146 metres long, with 1 service bridge and 27 gates |
| Owner | National government (MLIT) |
| Public Access | Laid out as a park |
References
- Okozu Diversion Weir (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/heritage/detail/101/00002624
- Tsubame cultural properties newsletter No. 11 (Tsubame City, Japanese)
- https://www.city.tsubame.niigata.jp/material/files/group/29/bunnkazaidayori11.pdf
- Designing in harmony with the surroundings (MLIT Shinano River office, Japanese)
- https://www.hrr.mlit.go.jp/shinano/shinanogawa_info/naruhodo/pdf/design35.pdf
Last verified: 2026.10.14