A Salt-Field Sluice on the Shore of Omishima
Iguchi Yonban-hama Minami Maruhi (井口四番浜南丸樋) is a late Edo-period granite sluice structure on the shore at Iguchi, Kamiura-cho, Imabari City, Ehime Prefecture, entered on the national register as a Registered Tangible Cultural Property on 31 January 2003. The Agency for Cultural Affairs dates it to the closing decades of the Edo period, between roughly 1830 and 1867, and records it as a single structure of stone, 12 meters long.
It stands on the eastern coast of Omishima, the largest island in the Geiyo archipelago, at the point where a salt field once met the sea. The salt fields at Iguchi were counted in numbered plots, each called a hama, and this structure served the southern edge of the fourth. A hi is a sluice, the channel cut through an embankment to move water; maru means round, and refers to the curved stone wall that shields the outlet. Three of these survive along this shore, and Iguchi Yonban-hama Minami Maruhi is the longest of them.
One Wall, Two Ways of Laying Stone
What makes Iguchi Yonban-hama Minami Maruhi worth stopping for is visible from a few meters away, once you know to look for it. The wall is granite, laid dry, without mortar or any binding agent. Its top measures 0.9 meters across, roughly the width of a footpath.
Look at the joints between the stones. Near the base they run diagonally, in a diamond pattern, and the face leans back from the vertical. Higher up the joints straighten out and run horizontally, and the face rises almost plumb. Two different masonry systems have been stacked in one wall.
The lower work is tanizumi, in which stones are set on the diagonal so the joints form a lattice of diamonds rather than a grid. Combined with the backward lean, called nori-kobai, it gives the wall a broad footing and a face that meets incoming water at an angle. The upper work is built in the manner of nunozumi, coursed masonry with joints running level, which is quicker to lay and perfectly adequate at a height that ordinary waves do not reach.
The switch happens where the sea stops being a constant problem. Builders working without mortar had one resource, which was the shape and placement of each block, and they spent it where the loads were. That decision is still legible in the stonework a century and a half later.
Why the Registration Matters
Iguchi Yonban-hama Minami Maruhi joined the Registered Tangible Cultural Property list on 31 January 2003 under registration number 38-0029, in the thirty-fifth round of registrations, with public notice following on 26 February of the same year. Imabari City owns it. The criterion applied was that the structure cannot easily be reproduced.
The reasoning behind that criterion is straightforward. Salt making along the Seto Inland Sea used the irihama method: seawater was let onto a levelled sand bed at high tide, concentrated by sun and wind, and the resulting brine boiled down over fires. A field of that kind needed water to move in both directions, and getting surplus water back out through the sea wall, without the outlet being destroyed in the first serious storm, was the harder half of the problem. The Agency for Cultural Affairs describes this structure as infrastructure that underpinned the local salt industry from the Edo period into the modern era, and notes that comparable examples are now scarce.
Scarce is an understatement. The irihama method was superseded during the twentieth century, the fields were filled in, and the earthworks went with them. Stone outlet works of this age survive in very few places. Three at Iguchi, on one stretch of coast, is unusual.
Visiting Iguchi Yonban-hama Minami Maruhi
The site is outdoors on the open shore. There is no gate, no admission charge, no opening hours, and no restriction on photography. There is also no visitor centre, no interpretive panel, and no dedicated parking, so plan to arrive on foot or by bicycle, or to park considerately elsewhere. Some adjoining land is privately owned. The stonework is itself a registered structure and not a place to climb, and it is best read from the public road and the shoreline beside it.
Tide governs what you can see. Around low water the full height of the wall is exposed and the diagonal work at the base is easy to trace; at high water the lower courses go under. Checking a tide table for the Imabari area before setting out is the single most useful piece of preparation.
Getting there is simple by road. Iguchi lies on the eastern coast of Omishima, roughly two kilometers north of the Omishima interchange on the Shimanami Kaido expressway and about 1.5 kilometers northwest of the Tatara Shimanami Park roadside station. By public transport, take an express bus bound for Omishima from in front of Imabari Station and alight at the Iguchi-ko stop, a few minutes on foot from the shore; services differ in which stops they call at, so check the timetable in advance. Cyclists riding the Shimanami Kaido pass within sight of it. Iguchi Yonban-hama Kita Maruhi stands about 100 meters to the northwest, and the Former Iguchi Sanban-hama Maruhi lies immediately to the south, which makes seeing all three a walk of a few minutes.
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Q&A
- What is Iguchi Yonban-hama Minami Maruhi, and when was it built?
- It is a stone sluice structure that drained a salt field on the east coast of Omishima in Ehime Prefecture. The Agency for Cultural Affairs dates it to the late Edo period, roughly 1830 to 1867, and records it as a single structure of granite, 12 meters long with a top width of 0.9 meters.
- What should I look at when I see Iguchi Yonban-hama Minami Maruhi?
- The joints. The lower part of the wall is laid in a diagonal tanizumi pattern with a backward lean, and the upper part switches to level coursing in the manner of nunozumi. The whole wall is dry-laid granite with no mortar. Following the line where one system gives way to the other shows how the builders matched the technique to the forces at each height.
- Can I visit Iguchi Yonban-hama Minami Maruhi, and is there an admission fee?
- Yes, and there is no charge. It sits outdoors on the shore with no gate and no set hours, and photography is unrestricted. There is no visitor facility or dedicated parking, and some neighbouring land is private, so view it from the adjacent public road and shoreline rather than climbing on the stonework.
- How do I get to Iguchi Yonban-hama Minami Maruhi by car or bus?
- By car, it is about two kilometers north of the Omishima interchange on the Shimanami Kaido, and roughly 1.5 kilometers northwest of the Tatara Shimanami Park roadside station. By bus, take an express service for Omishima from Imabari Station and get off at Iguchi-ko, a few minutes' walk away. Confirm the timetable first, since not every service stops there.
- Is there a good time of day to see Iguchi Yonban-hama Minami Maruhi?
- Tide matters more than time of day. Near low water the base of the wall and its diagonal masonry are fully exposed; at high water the lower courses are submerged. Consult a tide table for the Imabari area before you go.
Basic Information
| Name | Iguchi Yonban-hama Minami Maruhi (井口四番浜南丸樋) |
|---|---|
| Location | Coast of Iguchi, Kamiura-cho, Imabari City, Ehime Prefecture (Omishima) |
| Designation | Registered Tangible Cultural Property (structure), registration number 38-0029 |
| Year Designated | Registered 31 January 2003, public notice 26 February 2003 (35th round of registrations) |
| Quantity | 1 structure |
| Dimensions | Stone construction, 12 meters long, top width 0.9 meters |
| Owner | Imabari City |
| Public Access | Outdoors on the shore. Viewable at any time, no admission fee, no visitor facilities or dedicated parking |
References
- Agency for Cultural Affairs, National Cultural Properties Database: Iguchi Yonban-hama Minami Maruhi
- https://kunishitei.bunka.go.jp/heritage/detail/101/00003152
- Cultural Heritage Online: Iguchi Yonban-hama Minami Maruhi
- https://online.bunka.go.jp/heritages/detail/168462
- Agency for Cultural Affairs, National Cultural Properties Database: Former Iguchi Sanban-hama Maruhi
- https://kunishitei.bunka.go.jp/heritage/detail/101/00003151
- Imabari City Division of Cultural Promotion: Cultural Properties of the Kamiura District
- https://www.city.imabari.ehime.jp/bunka/bunkazai/bunkazai/kamiura.html
Last verified: 2026.09.03