Myojin River Reverse Water Sluice Gate

Myōjingawa Gyakusui Himon: A 1916 Stone Sluice Gate That Still Holds Back the Floods

Where the Myōjin River reaches the embankment of the larger Sakai River in the southern Aichi city of Ōbu, a squat stone arch carries the smaller stream through the dyke. This is the Myōjingawa Gyakusui Himon, completed in 1916 (Taishō 5). A himon is a sluice gate built into a flood embankment: it lets a minor watercourse pass through the bank while a closure prevents the main river from surging back the other way. The word gyakusui names exactly that danger, reverse flow, and the gate was made to stop it.

The waterway it shelters runs only a short distance further before the Myōjin River empties into the Sakai. The structure is modest in scale. Its conduit measures ten metres, formed of a single stone arch laid two courses thick, and its upper walls and the revetments flanking both banks are built up in a material that gives the gate its real significance: artificial stone, a tamped lime-and-earth construction that predates the spread of concrete in Japan.

More than a century after it was raised, the gate is still doing its job, channelling water through the bank as it was designed to.

Registered, Not Designated: Reading the Heritage Label

On 4 February 2021, the gate entered Japan's register of cultural properties as a Registered Tangible Cultural Property (tōroku yūkei bunkazai), under registration number 23-0561. For visitors used to seeing the terms "National Treasure" or "Important Cultural Property," the label here is worth a moment's explanation, because it belongs to a different system.

Japan runs two parallel frameworks. The older designation (shitei) system, dating to the prewar era, singles out the most exceptional objects and places under strict legal protection. The registration (tōroku) system was introduced only in 1996, and it works with a lighter touch. It was created to protect the broad stock of structures built roughly between the Meiji period and the mid-twentieth century, the everyday architecture and engineering of Japan's modernisation. Rather than freezing them under heavy restriction, it encourages owners to keep them in use. The Myōjingawa gate is a textbook case: a working piece of civil infrastructure conserved precisely because it still works.

The criterion recorded for its registration is that it is "not easily reproduced." That phrasing points to the construction method, which had effectively died out and could not simply be rebuilt with modern techniques.

Artificial Stone and the Engineer Behind It

The material in the gate's walls is jinzōseki, or artificial stone, a technique perfected by Hattori Chōshichi (1840–1919), a plasterer's son from nearby Hekinan in the same province. Hattori took tataki, the old practice of pounding a mix of slaked lime and decomposed granite soil into a hard floor or hearth, and reworked it into a water-resistant building material strong enough for harbours and embankments. His method, sometimes called "Chōshichi tataki," hardened even underwater, and in the decades before imported and then domestic cement took over, it built some of the most ambitious civil works of the age—the breakwater at Yokkaichi, the port at Ujina in Hiroshima, reclamation dykes along the coast.

The connection to this particular gate calls for care. Hattori retired from his business in 1904, twelve years before the Myōjingawa gate was completed. The Agency for Cultural Affairs records that the structure is thought to have been built by Aichi Prefecture on the basis of material tests that referenced Hattori's artificial stone, rather than by Hattori himself. The distinction matters: the gate is a product of his technique passing into wider engineering practice, carried on by the prefecture after the inventor had stepped away.

Its neighbour tells the other half of the story. A short walk away stands the Myōjin Himon, finished in 1901, whose records state plainly that Hattori was directly involved. The two gates were registered together on the same day in 2021, and read side by side they trace how one craftsman's invention became a regional standard.

What to Look For

The first thing to understand on the ground is that two waterways cross here at different heights. The Myōjin River passes over; the Gokason River, a drainage channel that local villages dug back in the Edo period to carry runoff from the rice fields, passes under. The 1901 Myōjin Himon handles the lower crossing of the Gokason River; the 1916 backflow gate carries the Myōjin River where it meets the Sakai embankment. Seen together, the pair is a compact lesson in how engineers stacked one flow above another to keep farmland drained without letting the big river in.

Look closely at the gate and you can still make out where a closure once sat—the marks of the vanished gate leaf that did the actual work of blocking backflow when the Sakai ran high. The Sakai River itself is no ordinary boundary: it traced the old border between Owari and Mikawa, the two historic provinces that together formed today's Aichi, so the embankment the gate pierces sits on a line that mattered for centuries.

This is industrial heritage rather than a manicured attraction. The setting is a working riverbank, and the structure can be partly screened by grass in the warmer months. Visitors drawn to the bones of how a landscape was engineered will find more here than those expecting a polished monument.

Around Ōbu

Ōbu sits on the JR Tōkaidō Main Line between Nagoya and Kariya, which makes the area an easy half-day outing from the city. A rapid train reaches Kyōwa Station from Nagoya in about thirteen minutes; Ōbu Station is the next stop down the line and connects to the Taketoyo branch toward the Chita Peninsula. From either station the gates lie out toward Yokone-chō on the city's eastern edge, by the Sakai River.

The registration of the two Myōjin gates brought Ōbu's tally of nationally registered tangible cultural properties to four. For travellers with an appetite for Japan's modern engineering heritage, the wider region rewards a look: the techniques pioneered in this corner of Aichi reappear in artificial-stone works across the prefecture and beyond, from the old Yokkaichi breakwater to the headworks of the Meiji Irrigation system.