What the Tatsunotoi Aqueduct Is
The Odai Irrigation Canal Tatsunotoi Aqueduct (小田井灌漑用水路龍之渡井, Odai Kangai Yōsuiro Tatsu-no-Toi) is a single-arch aqueduct of brick, stone and concrete built in 1919 to carry the Odai Irrigation Canal over the Anabuse River on the boundary between Nishinoyama in Kinokawa City and Takada in Katsuragi Town, Wakayama Prefecture, and it was registered as a Registered Tangible Cultural Property of Japan on March 2, 2006. The Agency for Cultural Affairs gives it a length of 21 meters and a width of 5.3 meters; it belongs to the Odai Land Improvement District.
Tatsu-no-toi means roughly "the dragon's aqueduct," toi (渡井) being a term for a water bridge that carries a canal. It carries registration number 30-0086 and was registered as a structure that would be difficult to reproduce. It is the largest of the canal's four registered structures. The Agency places it on the border of Naga Town and Katsuragi; Naga is now part of Kinokawa City.
The Hardest Crossing on the Odai Canal
MAFF, Japan's agriculture ministry, says the crossing of the Anabuse valley at the site of the Odai Irrigation Canal Tatsunotoi Aqueduct gave the builders more trouble than any other part of the canal dug from 1707. The first aqueduct was a wooden flume. It is said to have spanned the river, more than 18 meters wide, without a single intermediate post, resting on bedrock on either bank. Another MAFF page refers to the stream by a different name, 四十八瀬川.
The flume was often damaged by heavy rain and in 1919 was rebuilt in brick faced with stone. That makes it the last of the four registered structures to be rebuilt, ten years after the Koniwadani River Aqueduct.
A Stepped Arch and Stone Spandrels at Tatsunotoi
The Agency describes the arch of the Odai Irrigation Canal Tatsunotoi Aqueduct as seven bricks thick, its rings stepping outward one beyond the next. The other three registered structures have arches four bricks thick, so this one is nearly double. The spandrel walls are stone masonry, and above them rises a brick wall in Flemish bond (French bond, フランス積, in Japanese usage). The Agency calls the combination a distinctive structural form.
MAFF's feature page on the aqueduct says the fill above the arch is sanwa-do, a rammed mix of earth, lime and gravel, faced with natural stone. The ministry's figures are 20.5 meters long and 5.3 meters wide, with a channel 3.7 meters across, and it notes that apart from added handrails the structure keeps its original form.
Seeing the Tatsunotoi Aqueduct
The Odai Irrigation Canal Tatsunotoi Aqueduct is a working aqueduct with no reception desk or fee. MAFF notes that its top also serves as a path for local residents going to work and school. In October 2006 a sign explaining its history and role was put up.
The things to look at are the stepped seven-brick arch and the way the brick wall sits on top of the stone spandrels; the change of material shows clearly from the side of the bridge. Keep out of the channel, off its edges and out of the riverbed.
MAFF gives a 10-minute walk from Nishikaseda Station on the JR Wakayama Line, and in a straight line the aqueduct is about 550 meters from the station. Another MAFF page gives 30 minutes on foot from Nate or Nishikaseda. Getting around all four structures is covered on the Odai Irrigation Canal page.
Q&A
- When was the Odai Irrigation Canal Tatsunotoi Aqueduct built?
- The present aqueduct dates from 1919. The Edo-period crossing was a wooden flume that was often damaged by heavy rain, so it was rebuilt in brick and stone. It was registered as a Registered Tangible Cultural Property on March 2, 2006.
- How do you pronounce Odai Irrigation Canal Tatsunotoi Aqueduct in Japanese?
- Odai kangai yōsuiro tatsu-no-toi. A toi (渡井) is a water bridge that carries a canal over a stream.
- How big is the Odai Irrigation Canal Tatsunotoi Aqueduct?
- The Agency for Cultural Affairs lists it as 21 meters long and 5.3 meters wide. MAFF gives a length of 20.5 meters and a channel 3.7 meters across. It is the largest of the four registered structures.
- Why was the Odai Irrigation Canal Tatsunotoi Aqueduct so hard to build?
- The Anabuse River runs in a deep valley more than 18 meters wide here. According to MAFF, the Edo-period wooden flume rested on bedrock on both banks with no posts in between.
- Can I visit the Odai Irrigation Canal Tatsunotoi Aqueduct?
- Yes, from outside; there is no fee or reception, and the top is used as a local path. MAFF gives a 10-minute walk from Nishikaseda Station on the JR Wakayama Line.
Basic Information
| Name | Odai Irrigation Canal Tatsunotoi Aqueduct (小田井灌漑用水路龍之渡井) |
|---|---|
| Location | Nishinoyama, Kinokawa City to Takada, Katsuragi Town, Ito District, Wakayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2006 (registered) |
| Quantity | 1 |
| Dimensions | Length 21 meters, width 5.3 meters (single-arch bridge of brick, stone and concrete) |
| Owner | Odai Land Improvement District |
| Public Access | Working aqueduct; exterior can be viewed from nearby (no fee) |
References
- Agency for Cultural Affairs, Database of National Cultural Properties: Odai Irrigation Canal Tatsunotoi Aqueduct
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00005352
- MAFF, Cultural Heritage of Rural Infrastructure: Odai Irrigation Canal Tatsunotoi Aqueduct (Japanese)
- https://www.maff.go.jp/j/nousin/sekkei/museum/m_bunka/yuukei7/index.html
- MAFF, Tatsunotoi: An Aqueduct Recalling the Work of Ohata Saizo (Japanese)
- https://www.maff.go.jp/j/nousin/sekkei/museum/m_kakuti/40_tatuno/index.html
Last verified: 2026.10.07
