Mase Dam Management Bridge: An Early Showa Engineering Treasure
Tucked away in the green hills of Kodama, Honjo City, Saitama Prefecture, the Mase Dam Management Bridge (間瀬堰堤管理橋) stands as a quiet yet compelling monument to Japan's pre-war civil engineering heritage. Built in 1938 (Showa 13), this reinforced concrete girder bridge was constructed as an integral component of the Mase Dam — the oldest surviving agricultural gravity concrete dam in eastern Japan. Together with the dam itself, the management bridge was registered as a national Tangible Cultural Property (登録有形文化財) in October 2000, preserving a valuable piece of Japan's modern engineering history for future generations.
Historical Background
The Mase Dam was conceived in the Taisho era to address recurring flood damage and irrigation shortages along the Mase River, a tributary of the Tone River system. Construction spanned eight years from 1930 (Showa 5) to 1937 (Showa 12), resulting in an imposing gravity-type concrete dam standing 27.5 meters high and stretching 126 meters across the valley, with a total storage capacity of 530,000 cubic meters. The dam was designed by the engineer Ikuzo Takahori and serves as the central facility of the Kodama irrigation system.
The management bridge was erected the following year in 1938, positioned downstream of the dam's water conveyance channel. It was designed to provide maintenance access across the spillway, functioning as part of the dam's essential operational infrastructure. The bridge features a distinctive design with four bridge piers, each with arched openings carved into their lower portions, along with grooves for stop logs — reflecting the practical engineering requirements of dam management during the early Showa period.
Why It Was Designated a Cultural Property
The Mase Dam Management Bridge received its registration as a Tangible Cultural Property in recognition of several important qualities. As a three-span reinforced concrete girder bridge measuring 9.5 meters in length and 2.0 meters in width, it represents a well-preserved example of pre-war concrete bridge construction techniques in Japan. Its bridge piers, with their gracefully arched lower openings and functional stop-log grooves, demonstrate the aesthetic sensibility that early Showa engineers brought even to utilitarian infrastructure.
The bridge also holds significance as an inseparable component of the Mase Dam complex, which itself is recognized as a pioneering agricultural engineering achievement. The dam is listed among the Japan Society of Civil Engineers' "2000 Selected Important Civil Engineering Structures of Modern Japan," underscoring the entire complex's place in the nation's civil engineering heritage. Together, the dam and bridge illustrate the scale and ambition of pre-war agricultural improvement projects that transformed rural communities across Japan.
Highlights and What to See
Visitors to the Mase Dam Management Bridge will appreciate several distinct features. The bridge itself, though compact in scale, exhibits the solid craftsmanship of 1930s concrete construction. The arched openings beneath the piers create an elegant visual rhythm, and the entire structure has weathered beautifully over nearly nine decades, lending it a patina that speaks to its enduring quality.
The dam complex offers a rewarding experience as well. The main dam body features a wooden two-story water intake tower, faux-timber railings along the crest, and a central overflow-type spillway. Visitors can approach the base of the dam from the left bank plaza, where the impressive scale of the structure becomes fully apparent.
The reservoir formed by the dam is known as Lake Mase (間瀬湖), located within the Jobu Natural Park. The lake and surrounding landscape have been recognized as one of Japan's "New 100 Scenic Views" (1957), selected for the "Furusato Saitama 100 Selections" (1984), and included in the "Tone River 100 Views" (1986). In spring, cherry blossoms ring the lake and reflect in the still water, while autumn brings vivid foliage from the surrounding mountains. The area also serves as a popular spot for fishing, particularly for crucian carp (herabuna) and smelt (wakasagi).
Surrounding Area and Nearby Attractions
The Kodama area of Honjo City offers several additional attractions that pair well with a visit to the Mase Dam complex.
- Joshinin Hyakutai Kannon-do (Sazae-do): One of Japan's Three Great Sazae-do halls, this unique spiral-structured Buddhist temple houses 100 Kannon statues across three interior levels. Visitors can complete a pilgrimage to 100 sacred sites simply by walking through the building. Advance reservation required through the Honjo Tourism Agriculture Center.
- Hanawa Hokiichi Memorial Museum: A free museum dedicated to the renowned blind Edo-period scholar Hanawa Hokiichi, who compiled the monumental "Gunsho Ruiju" literary anthology. The museum displays approximately 200 artifacts and personal belongings.
- Chosenji Temple — Kotsuhata no Fuji: Home to a magnificent wisteria tree estimated to be over 650 years old, designated as a Saitama Prefectural Natural Monument. The cascading flower clusters reach up to 1.5 meters in length, with peak bloom from late April to mid-May.
- Honjo Tourism Agriculture Center: Located near the Sazae-do, this facility serves as a visitor hub where dam cards for Mase Dam are available, and where visitors can arrange access to local cultural sites.
Seasonal Guide
Each season brings a different character to the Mase Dam area. Spring (late March to mid-April) is the most popular time, when cherry blossoms create a stunning frame around Lake Mase. Summer offers lush greenery and cool breezes from the lake. Autumn (late October to November) transforms the surrounding mountains into a tapestry of red and gold foliage reflected in the water. Winter provides clear, quiet views of the dam and bridge against bare mountain slopes, ideal for those seeking solitude and unobstructed photography of the structures.
- 📍 Plan Your Visit to Saitama
- Find tours, activities & transport passes near Mase Weir Management Bridge
- [ Kawagoe Little Edo & Moominvalley Park ]
Q＆A
- Is there an admission fee to visit the Mase Dam and Management Bridge?
- No, visiting the Mase Dam, Management Bridge, and Lake Mase is free of charge. If you wish to fish in the lake, a day fishing permit costs 400 yen (500 yen if purchased on-site).
- How do I get to the Mase Dam from Tokyo?
- By car, take the Kan-Etsu Expressway to the Honjo-Kodama IC, then drive approximately 20 minutes (about 7 km). By train, take the JR Hachiko Line to Kodama Station, then a taxi for about 10 minutes. A community bus (Hanipon-go) also runs to the "Mase-ko Entei" stop, though advance reservation by phone is required.
- Is the bridge open to pedestrians?
- The management bridge and the dam crest are accessible as part of a walking path in the area. Recent improvements have integrated the bridge into a pleasant walking trail enjoyed by local residents and visitors alike. However, the dam crest road is narrow due to its original design, so please exercise caution.
- When is the best time to visit?
- Spring (late March to mid-April) for cherry blossoms and autumn (late October to November) for foliage are especially scenic. However, each season has its own appeal, and winter offers the clearest views of the dam and bridge structures.
- Are there English signs or guides available at the site?
- Signage at the site is primarily in Japanese. It is recommended to prepare information in advance or use a translation app on your smartphone. The nearby Honjo Tourism Agriculture Center may be able to provide basic assistance.
Basic Information
| Name | Mase Dam Management Bridge (間瀬堰堤管理橋) |
|---|---|
| Cultural Property Designation | Registered Tangible Cultural Property (Building) — Registered October 18, 2000 |
| Year Built | 1938 (Showa 13) |
| Structure | Three-span reinforced concrete girder bridge; length 9.5 m, width 2.0 m |
| Location | Kodaira, Kodama-machi, Honjo City, Saitama Prefecture 367-0214 |
| Owner | Bikozawa Irrigation Land Improvement District (美児沢用水土地改良区) |
| Related Structure | Mase Dam (間瀬堰堤) — also a Registered Tangible Cultural Property, completed 1937; designed by Ikuzo Takahori |
| Access | Approx. 20 min by car from Honjo-Kodama IC (Kan-Etsu Expressway); approx. 10 min by taxi from JR Kodama Station (Hachiko Line) |
| Admission | Free |
References
- 間瀬堰堤管理橋 — 文化遺産オンライン
- https://bunka.nii.ac.jp/heritages/detail/181813
- 間瀬堰堤 — 文化遺産オンライン
- https://bunka.nii.ac.jp/heritages/detail/167212
- 間瀬堰堤 — 農林水産省
- https://www.maff.go.jp/j/nousin/sekkei/museum/m_bunka/yuukei1/index.html
- 間瀬湖 — 本庄市観光協会
- https://www.honjo-kanko.jp/sightseeing/maze-ko.html
- 間瀬湖 — ちょこたび埼玉（埼玉県公式観光サイト）
- https://chocotabi-saitama.jp/spot/40826/
- 成身院百体観音堂（さざえ堂） — 本庄市観光協会
- https://www.honjo-kanko.jp/sightseeing/hyakutaikannon-do.html
Last verified: 2026.03.26