A Stone Drain Built Against the Sea
The Former Iguchi Sanban-hama Maruhi (旧井口三番浜丸樋, Kyū-Iguchi Sanban-hama Maruhi) is a late Edo-period stone sluice structure standing on the shoreline at Iguchi, Kamiura-cho, Imabari City, Ehime Prefecture, built between roughly 1830 and 1867 and entered on the national register of Tangible Cultural Properties in January 2003. It served the salt fields that once occupied this stretch of the eastern coast of Omishima, the largest island in the Geiyo archipelago.
The name repays unpacking. Hama was the unit by which salt fields were counted, and sanban-hama means the third field in the sequence at Iguchi. A hi is a sluice or culvert, the channel cut through an embankment to move water. Maru, round, describes what makes this one worth a national listing.
Salt making on the Seto Inland Sea coast used the irihama method, in which seawater was admitted onto a levelled sand bed at high tide, concentrated by sun and wind, and the resulting brine boiled down. The system depended on controlling water in both directions. Letting the sea in was one problem. Getting surplus water back out, reliably and without the outlet being torn apart by weather, was the other, and it is the one this structure answers.
The Curve That Earned the Listing
The Agency for Cultural Affairs records the property as a single structure of stone construction with a length of 8.5 meters, dated to the closing decades of the Edo period. It was registered on 31 January 2003 under registration number 38-0028, in the thirty-fifth round of registrations, with public notice following on 26 February. Imabari City owns it. The registration criterion applied was that the structure is not easily reproduced, a category reserved for work whose technique or circumstances cannot readily be recreated.
The stonework sits along the embankment where the shoreline meets the edge of the former salt field. Its distinguishing feature is a wall that projects seaward in a semicircular arc, running 8.5 meters around the outlet. The geometry does two jobs at once. It leaves the drainage path open so that surplus water can leave the field, while presenting a curved face to incoming waves rather than a flat one, so that storm swell is deflected around the opening instead of striking the sluice head-on. Anyone who has watched wind-driven water hit a straight seawall will recognise the reasoning immediately.
Very little Edo-period salt-field infrastructure survives anywhere in Japan. The irihama method gave way to newer techniques during the twentieth century, and the last of the country's salt fields were retired by 1971 under industrial reorganisation. The ponds were filled, the embankments levelled, the land turned over to orchards or housing. Where the earthworks vanished, the stonework generally went with them. This is one reason the listing matters more than the modest dimensions might suggest.
Visiting, and What Else Is Nearby
A second registered structure survives immediately to the north. The Iguchi Yonban-hama Minami Maruhi is built of granite, runs 12 meters in length with a top width of 0.9 meters, and is laid dry without mortar: the lower courses in a diagonal tanizumi pattern to give the face its batter, the upper courses set nearly vertical in a coursed style. Seeing the two together shows how the technique varied field by field along a single stretch of coast.
The site is outdoors on the shore, with no gate, no admission charge, and no set hours. There is no visitor centre, no interpretive signage of the kind you would find at a major site, and no dedicated parking. Some of the surrounding land is privately held, and the stonework itself is a heritage structure rather than something to climb on, so it is best appreciated from the adjacent public road and shoreline. Photography is unrestricted.
Tide matters here more than time of day. At low water the full run of the curved wall and its footing are exposed; at high water the lower courses disappear. Checking a tide table for the Imabari area before setting out is the single most useful piece of preparation.
Getting there is straightforward if you are already on the Shimanami Kaido, the cycling and driving route that links Onomichi in Hiroshima with Imabari across a chain of bridges. The Omishima interchange is close by, and the road running past this shore is the one most visitors take toward Oyamazumi Shrine, the island's principal site, whose treasure hall holds an exceptional collection of medieval arms and armour. Cyclists pass this point in numbers; almost none of them stop. Ten minutes off the saddle is enough to see both sluices.
- 📍 Plan Your Visit to Ehime
- Find tours, activities & transport passes near Old Iguchi Sanbanhama Maru Canal
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Q&A
- What exactly is the Former Iguchi Sanban-hama Maruhi?
- It is a stone sluice structure built into the sea embankment of a former salt field on Omishima, dating to the last decades of the Edo period. Its main function was draining surplus water from the salt field, and a semicircular stone wall 8.5 meters long projects seaward around the outlet to protect it from wave damage.
- Can I visit the Former Iguchi Sanban-hama Maruhi, and is there an admission fee?
- Yes, and there is no charge. The structure stands in the open on the shoreline at Iguchi with no gate or opening hours. There is no visitor facility or dedicated parking, and neighbouring land is partly private, so view it from the adjacent public road and shore.
- When is the best time of day to see the Former Iguchi Sanban-hama Maruhi?
- Around low tide. The curved wall and its lower courses are fully exposed at low water and partly submerged at high water, so a tide table for the Imabari area is worth consulting before you go. Photography is unrestricted at any hour.
- How do I reach the Former Iguchi Sanban-hama Maruhi on Omishima?
- It lies on the eastern shore at Iguchi, near the Omishima interchange on the Shimanami Kaido expressway that connects Onomichi and Imabari. The coastal road passing the site is the usual route toward Oyamazumi Shrine, which makes it easy to combine by car or bicycle.
- Are there other registered salt-field structures near the Former Iguchi Sanban-hama Maruhi?
- Yes. The Iguchi Yonban-hama Minami Maruhi stands just to the north and is also a Registered Tangible Cultural Property. It is a dry-laid granite structure 12 meters long with a top width of 0.9 meters, and comparing the two shows how construction methods differed between adjacent salt fields.
Basic Information
| Name | Former Iguchi Sanban-hama Maruhi (旧井口三番浜丸樋) |
|---|---|
| Location | Shore at Iguchi, Kamiura-cho, Imabari City, Ehime Prefecture (Omishima) |
| Designation | Registered Tangible Cultural Property (Structure), registration no. 38-0028 |
| Year Designated | Registered 31 January 2003; public notice 26 February 2003 (35th round of registration) |
| Quantity | 1 structure |
| Dimensions | Stone construction, length 8.5 m |
| Owner | Imabari City |
| Public Access | Outdoor shoreline site, freely viewable at all times, no admission charge, no visitor facilities |
References
- National Cultural Properties Database, Agency for Cultural Affairs: Former Iguchi Sanban-hama Maruhi
- https://kunishitei.bunka.go.jp/heritage/detail/101/00003151
- Cultural Heritage Online: Former Iguchi Sanban-hama Maruhi
- https://online.bunka.go.jp/heritages/detail/140421
- Cultural Heritage Online: Iguchi Yonban-hama Minami Maruhi
- https://online.bunka.go.jp/heritages/detail/168462
- Imabari City, Division of Cultural Promotion: Cultural Properties of the Omishima Area
- https://www.city.imabari.ehime.jp/bunka/bunkazai/bunkazai/omisima.html
Last verified: 2026.08.06