What the Nakatani River Water Gate Is
The Odai Irrigation Canal Nakatani River Water Gate (小田井灌漑用水路中谷川水門, Odai Kangai Yōsuiro Nakatanigawa Suimon) is a brick inverted siphon built in 1912 where the Odai Irrigation Canal crosses the Nakatani River at Nakaiburi, Katsuragi Town, Ito District, Wakayama Prefecture, and it was registered as a Registered Tangible Cultural Property of Japan on March 2, 2006. The Agency for Cultural Affairs lists it as 13 meters long and 6.4 meters wide, and it belongs to the Odai Land Improvement District.
It carries registration number 30-0088 and was registered as a structure that would be difficult to reproduce. Of the four registered structures on the canal, it is the farthest upstream. Here the channel, which runs west roughly parallel to the Kinokawa River, meets a short stream coming down from the Izumi Mountains.
A Water Gate That Runs Under the River
Despite the name, the Odai Irrigation Canal Nakatani River Water Gate does not open or shut to control flow. The Agency describes it as a culvert built beneath the river where the canal and the Nakatani meet, working on the siphon principle, and MAFF, Japan's agriculture ministry, likewise calls it a siphon laid to take the canal under the river.
In an inverted siphon the canal water drops into a lower conduit before the stream, passes under the riverbed and rises back to channel level on the far side. As long as the water surface at the inlet sits higher than at the outlet, gravity does the work. The other three registered structures on the canal are aqueducts that carry the water over their streams; this is the only one that goes under.
MAFF says the original crossing was made of timber and was often damaged in heavy rain, so it was rebuilt in brick in 1912. The ministry gives 13.3 meters between the gates at either end and a channel width of 6.4 meters, close to the Agency's figures. Wakayama Prefecture's river plan calls the stream "Nakatani River (Nakaiburi)" to tell it apart from another Nakatani River elsewhere in Katsuragi.
Brickwork of the Nakatani River Water Gate
According to the Agency, the arch of the Odai Irrigation Canal Nakatani River Water Gate is four bricks thick, the walls are laid in Flemish bond (called French bond, フランス積, in Japan), and a Parapet rises along the top. In Flemish bond each course alternates the long face and the short end of the brick, which gives the wall a steady checkered rhythm.
The Agency sees the structure as evidence of how a large irrigation canal dug under the Edo-period domain was modernized. MAFF notes that it keeps nearly its original form and still serves the canal, which waters about 610 hectares of paddies.
Seeing the Nakatani River Water Gate
The Odai Irrigation Canal Nakatani River Water Gate is a working irrigation structure. There is no reception desk or admission fee, and it is viewed from the roads around it. Keep out of the channel and away from its edges.
Look for the brick arch, the parapet above it and the bond pattern of the walls. The conduit under the river cannot be seen, but finding the point where the open channel disappears below ground makes the siphon easy to picture.
The nearest station is Nakaiburi on the JR Wakayama Line, about 250 meters away in a straight line. MAFF's page gives a 10-minute walk from Kaseda Station, but Kaseda lies about 5 kilometers to the west. Getting around all four structures is covered on the Odai Irrigation Canal page.
Q&A
- When was the Odai Irrigation Canal Nakatani River Water Gate built?
- In 1912. The crossing was timber when the canal was dug in the Edo period and was rebuilt in brick after repeated flood damage. It was registered as a Registered Tangible Cultural Property on March 2, 2006.
- What does the Odai Irrigation Canal Nakatani River Water Gate actually do if it is not a gate?
- It is an inverted siphon that takes the canal under the Nakatani River. The Agency for Cultural Affairs describes it as a culvert beneath the river working on the siphon principle; it does not regulate flow.
- How big is the Odai Irrigation Canal Nakatani River Water Gate?
- The Agency lists it as 13 meters long and 6.4 meters wide. MAFF gives 13.3 meters between the gates at either end and a channel width of 6.4 meters.
- What should I look for at the Odai Irrigation Canal Nakatani River Water Gate?
- The four-brick-thick arch, the Flemish bond walls with alternating long and short brick faces, and the parapet along the top. Watching where the open channel drops out of sight shows how the siphon works.
- How do I get to the Odai Irrigation Canal Nakatani River Water Gate?
- Nakaiburi Station on the JR Wakayama Line is the closest, about 250 meters away in a straight line. There is no fee or reception; view it from the surrounding roads and keep clear of the channel.
Basic Information
| Name | Odai Irrigation Canal Nakatani River Water Gate (小田井灌漑用水路中谷川水門) |
|---|---|
| Location | Nakaiburi, Katsuragi Town, Ito District, Wakayama Prefecture |
| Designation | Registered Tangible Cultural Property (Structure) |
| Year Designated | 2006 (registered) |
| Quantity | 1 |
| Dimensions | Length 13 meters, width 6.4 meters (brick) |
| Owner | Odai Land Improvement District |
| Public Access | Working irrigation structure; exterior can be viewed from nearby (no fee) |
References
- Agency for Cultural Affairs, Database of National Cultural Properties: Odai Irrigation Canal Nakatani River Water Gate
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00005354
- MAFF, Cultural Heritage of Rural Infrastructure: Odai Irrigation Canal Nakatani River Water Gate (Japanese)
- https://www.maff.go.jp/j/nousin/sekkei/museum/m_bunka/yuukei10/index.html
- Wakayama Prefecture, River Improvement Plan for the Kisen Area of the Kinokawa System (Japanese, PDF)
- https://www.pref.wakayama.lg.jp/prefg/080400/keikaku/seibikeikaku_d/fil/kisenkeniki_keikaku.pdf
Last verified: 2026.10.07
