A Working Dam of 1929, Built by the Farmers Who Needed It
Hōnen-ike Entei (豊稔池堰堤, the Hōnen-ike Dam) is a concrete irrigation dam on the upper Kunita River at Tanono, Ōnohara-chō, Kan'onji City, Kagawa Prefecture, completed in November 1929 and designated an Important Cultural Property on 19 December 2006. It measures 145.5 metres along the crest and stands 30.4 metres high.
Kagawa has the smallest land area of any Japanese prefecture and, historically, some of its least reliable rainfall. The Sanuki plain is dotted with thousands of irrigation ponds because the alternative was crop failure. Two severe droughts in the Taishō era pushed local farmers on the Ōnohara side of the prefecture to ask for something more ambitious than another earth-banked pond.
Work began in March 1926 under the prefecture's irrigation and drainage improvement programme. Sano Tōjirō advised as consultant, the agricultural engineer Sugiura Midori supervised, the design came from the local agricultural engineer Kimura Shingorō, and Suzuki Nobuo ran the site. Construction ran three years and eight months. What makes the story unusual is the labour: the work was carried out by the farming households who would receive the water, organised into work gangs, and local accounts hold that it was completed without a fatal accident.
The reservoir was known through construction as Tanono-ike, after the hamlet. In May 1929 the finance minister Mitsuchi Chūzō visited the site and is said to have renamed it Hōnen-ike, the pond of abundant harvest. The formal opening followed in March 1930.
Two Structural Systems in One Wall
The dam sits on a bed of sandstone, shale, and tuff where the Kunita River narrows. What draws people here is the middle section: five arches carried between six buttresses, curving upstream in a row. That form is the multiple-arch dam, and it is one of only a handful ever built in Japan.
The engineering runs deeper than the silhouette. The two end sections are conventional gravity dams, solid and non-overflow, holding back water by weight alone. The central 87 metres uses the multiple-arch system, of which the middle 53.2 metres is designed to be overtopped. Six buttresses stand at 14.5-metre centres, set at a slight incline, and each carries a segmental arch of water-facing wall. The arches pass load along the axis of the dam into the gravity sections at either end. Combining the two systems in a single structure let the builders match each part to the ground beneath it.
The dam is often described as a masonry structure, and photographs support the impression. The body is concrete. Coursed sandstone ashlar faces the gravity sections and most of the rest, with concrete blocks at the downstream arch faces and the outer corners of the buttresses. The stone is a skin over a concrete core, which is precisely why the dam counts as one of Japan's earliest concrete irrigation dams rather than as a late example of the older tradition.
One more device deserves attention. The four central buttresses carry siphon spillways that discharge automatically when the reservoir fills, spreading the pressure of falling water across the ground downstream instead of concentrating it. A stone-paved apron takes the impact. Getting overflow off a dam without undermining its own foundations was the hard problem on this site, and the answer was inventive enough that the designation text singles it out.
Attached items are protected alongside the dam: the Hōnen-ike monument on the crest of the southern gravity section, with bronze plates recording the construction and the engineers involved and a border of rice, wheat, and birds; two former powder magazines whose reinforced concrete walls survive from the blasting work; and an original sluice gate and intake valve replaced during later repairs.
Visiting: Free, Open, and Best in Late Summer
There is no admission charge and no gate. Hōnen-ike Yūsui Park sits directly below the dam, a small grassed area completed in 1995 with a pavilion and a short walking route, and from there the wall rises above you at full height. This is the view that earns the dam its usual comparison to a European castle. Fireflies appear along the stream in early summer.
Prefectural Route 9 runs past the top, giving a second angle onto the crest and the arch heads. Climbing to the reservoir side is possible by a flight of steps near the old powder magazine, and the water spreads out between the ridges of the Asan range. Walking along the crest itself is prohibited.
The event worth timing a trip around is the yurunuki, the opening of the sluice. Water is released to supply the paddies downstream, and the discharge reaches around four tonnes per second with a roar that carries down the valley. It happens once a year, generally between late July and early August, with the timing judged by when the storage in Iseki-ike below drops to about thirty per cent. The date is not fixed in advance and the release has been cancelled in some years, so check with Kan'onji City or the local tourism association before travelling for it.
Reaching the dam is easiest by car: about 25 minutes from JR Kan'onji Station, or 15 minutes from the Ōnohara interchange on the Takamatsu Expressway. The side road down to the car park is narrow and the parking area is small, which becomes a problem on release days when photographers arrive in numbers. Community buses on the Gogō-Takamuro route run four times daily, of which two, the services bound for Tanono, pass the dam; tell the driver you want Hōnen-ike, as the route has no fixed stops and passengers board and alight anywhere along it.
The dam is not a monument in retirement. It still irrigates roughly 500 hectares of farmland, and the reservoir holds around 1.59 million tonnes. That continuing function is part of what is being conserved.
- 📍 Plan Your Visit to Kagawa
- Find tours, activities & transport passes near Toyonori Pond Dam
- [ Naoshima Art Island & Kotohiragu Shrine Visit ]
Q&A
- Can you visit Hōnen-ike Dam, and is there an admission charge?
- Access is free and unrestricted at any time of day. Hōnen-ike Yūsui Park below the dam gives the best view of the arches from the base, and Prefectural Route 9 passes the crest. Walking along the top of the dam is prohibited.
- When is the yurunuki water release at Hōnen-ike Dam?
- Usually once a year between late July and early August, timed by the storage level in Iseki-ike downstream rather than by a fixed calendar date. Roughly four tonnes of water per second are discharged. The release has been cancelled in some years, so confirm with Kan'onji City or the Kan'onji Tourism Association before travelling for it.
- Why is Hōnen-ike Dam an Important Cultural Property?
- It was designated on 19 December 2006 as one of Japan's earliest concrete irrigation dams and for its combination of arch and buttress construction in one structure. The designation criteria cited are technical excellence and high historical value, and the siphon spillways devised to cope with the ground conditions are singled out.
- Is Hōnen-ike Dam built of stone or concrete?
- Concrete, faced with coursed sandstone ashlar over most of the surface and concrete blocks at the downstream arch faces and buttress corners. The masonry appearance leads to it being described as a stone dam, but the structural body is concrete, which is why it counts among the earliest of its kind in Japan.
- How do you get to Hōnen-ike Dam from JR Kan'onji Station?
- About 25 minutes by car, or 15 minutes from the Ōnohara interchange. Community buses on the Gogō-Takamuro route run four times a day, two of which, the Tanono services, pass the dam; there are no fixed stops, so tell the driver your destination. The access lane is narrow and parking is limited.
Basic Information
| Name | Hōnen-ike Entei (豊稔池堰堤) |
|---|---|
| Location | Tanono, Ōnohara-chō, Kan'onji City, Kagawa Prefecture |
| Designation | Important Cultural Property (Structure), designation no. 02498 |
| Year Designated | 19 December 2006 |
| Quantity | 1 site; attached items: Hōnen-ike monument 1, former powder magazines 2, former sluice gate 1, former intake valve 1 |
| Dimensions | Multiple-arch concrete dam, crest length 145.5 m, height 30.4 m; multiple-arch section 87.0 m, of which 53.2 m overflow |
| Owner | Hōnen-ike Land Improvement District |
| Public Access | Freely accessible at all times, no charge; walking on the crest prohibited. Yurunuki release late July to early August, date not fixed |
References
- National Database of Cultural Properties, Agency for Cultural Affairs — Hōnen-ike Entei
- https://kunishitei.bunka.go.jp/heritage/detail/102/00004075
- Cultural Heritage Online — Hōnen-ike Entei
- https://online.bunka.go.jp/heritages/detail/158595
- Kan'onji City — Hōnen-ike Entei, Cultural Properties Section
- https://www.city.kanonji.kagawa.jp/soshiki/30/563.html
- Kan'onji City — Hōnen-ike Entei, Tourism Pages
- https://www.city.kanonji.kagawa.jp/soshiki/21/334.html
- Kan'onji Tourism Association — Hōnen-ike Entei
- https://kanonji-kanko.jp/honen-pond/
- Kan'onji Tourism Association — Hōnen-ike Yurunuki
- https://kanonji-kanko.jp/honen-pond-yurunuki/
- Kagawa Prefecture Tourism Association — Hōnen-ike Entei
- https://www.my-kagawa.jp/point/67/
Last verified: 2026.08.09