Introduction
Nestled deep in the mountain ravines of Ōyama in Isehara City, Kanagawa Prefecture, the Fukuromachi Dam (袋町堰堤) stands as a remarkable testament to Japan's early modern approach to disaster prevention engineering. Built in 1929, this gravity-type concrete sabo dam was constructed in the wake of the devastating 1923 Great Kantō Earthquake, which triggered massive landslides across the Tanzawa mountain range. Registered as a nationally designated tangible cultural property in 2004, the Fukuromachi Dam represents a fascinating intersection of civil engineering, natural disaster history, and sacred mountain pilgrimage culture that continues to protect both the communities and the ancient pilgrimage routes leading to the revered peak of Mt. Ōyama.
Historical Background
The Great Kantō Earthquake of September 1, 1923, not only devastated Tokyo and Yokohama but also caused catastrophic damage to the Tanzawa mountain range in western Kanagawa Prefecture. Approximately 20% of the Tanzawa mountain area—roughly 6,000 hectares—suffered severe slope failures and landslides. In the years that followed, continued rainfall and subsequent seismic events, including the 1930 North Izu Earthquake, further destabilized the terrain, sending debris and sediment cascading into the rivers and streams that flowed through the valleys below.
The Suzukawa River, which originates from Mt. Ōyama and flows southward through Isehara, was particularly vulnerable. The mountain streams feeding into the Kanamegawa river system, including the Fudōsawa stream where the Fukuromachi Dam stands, posed a direct threat to the settlements and pilgrimage infrastructure at the foot of the sacred mountain. In response, Kanagawa Prefecture launched sabo (erosion control) construction projects beginning in 1927, and the Fukuromachi Dam was completed in 1929 as part of this comprehensive effort to stabilize the ravaged landscape.
Why It Was Designated as a Cultural Property
The Fukuromachi Dam was registered as a nationally registered tangible cultural property (building) on July 23, 2004, under the criterion that it contributes to Japan's national historical landscape. Together with two companion dams in the same area—the Hachidan Dam (eight-tiered dam, 37 meters long and 11 meters high) and the Motodaki Dam (25 meters long and 4.3 meters high)—the Fukuromachi Dam forms a trio of early Shōwa-era sabo structures that document Japan's pioneering disaster prevention efforts following the Great Kantō Earthquake.
These dams were built using a distinctive trapezoidal rubble masonry technique, stacking stone and concrete in a method that is difficult to replicate with modern construction practices. Beyond their engineering significance, the dams are valued for their harmonious integration into the mountain landscape, quietly performing their protective function while blending into the natural environment of the Ōyama foothills for nearly a century.
Architectural and Engineering Highlights
The Fukuromachi Dam is a gravity-type rubble masonry concrete dam measuring 24 meters in length and 6.0 meters in height. Its design features a uniform slope gradient of 3/10 on both the upstream and downstream faces, creating a robust trapezoidal cross-section that relies on its own weight to resist the force of water and debris. The spillway (water passage) is strategically positioned on the left bank side, close to the natural bedrock, maximizing the structural integrity of the overflow channel.
What makes this dam particularly noteworthy is its dual purpose. Built on the Fudōsawa stream within the Kanamegawa river system, the dam was designed not only to prevent sediment and debris from reaching the downstream settlements but also to protect the ancient pilgrimage route leading to the sacred summit of Mt. Ōyama. The pilgrimage path, which has been used by worshippers for centuries, passes in close proximity to the dam, and the structure has quietly safeguarded both human lives and spiritual heritage since its completion.
Mt. Ōyama and the Pilgrimage Tradition
Mt. Ōyama (1,252 meters) has been a center of mountain worship since ancient times. Known also as "Afuri-yama" (Rain-Bringing Mountain), the peak is home to the Ōyama Afuri Shrine, whose origins are said to date back over 2,200 years. During the Edo period, "Ōyama-mairi" (Ōyama pilgrimage) became enormously popular among the common people, with over 15,700 pilgrimage groups and approximately 700,000 households participating in the tradition. This cultural phenomenon has been recognized as a Japan Heritage site.
The Fukuromachi Dam sits along the streams near these historic pilgrimage routes, serving as an invisible guardian of the sacred landscape. The fact that disaster prevention infrastructure was built specifically to protect not just residential areas but also the spiritual pathways of pilgrimage speaks to the deep cultural significance of Mt. Ōyama in the lives of the people of this region.
Visitor Information
It is important to note that the Fukuromachi Dam and the nearby Hachidan Dam are located within restricted access areas and cannot be directly visited or viewed by the public. However, the companion Motodaki Dam can be seen from the Kumoi Bridge along the hiking trail leading to Mt. Ōyama, offering visitors a glimpse of these historic sabo structures.
Visitors to the Ōyama area can enjoy a wealth of cultural and natural attractions. From Isehara Station on the Odakyu Line, buses run to the Ōyama Cable Car station (approximately 30 minutes). The cable car ascends 278 meters in about 6 minutes, passing through the atmospheric Koma Sandō shopping street, to reach Ōyama Afuri Shrine's Lower Shrine at an elevation of approximately 700 meters. The area is celebrated for its seasonal beauty—cherry blossoms in spring, lush greenery in summer, vivid autumn foliage, and serene winter snowscapes.
For those arriving by car, the Shin-Tōmei Expressway's Isehara-Ōyama Interchange provides convenient access to the area.
Surrounding Attractions
The Ōyama area offers numerous points of interest beyond the dam itself. Ōyama Afuri Shrine, with its spectacular panoramic views rated two stars in the Michelin Green Guide Japan, is the region's foremost attraction. Ōyama-dera Temple, accessible via a stop on the cable car line, is known for its stunning autumn foliage. The Koma Sandō approach road features traditional shops selling Ōyama tofu—made with pure mountain spring water—and the famous Ōyama spinning tops (koma), a designated cultural craft. The area's ryokan (traditional inns) offer visitors a chance to experience the atmosphere of the old pilgrimage lodging houses that have served travelers for centuries.
- 📍 Plan Your Visit to Kanagawa
- Find tours, activities & transport passes near Fukuromachi Dam
- [ Kamakura Buddha Hakone Onsen & Yokohama Tours ]
Q＆A
- What is the Fukuromachi Dam and why is it culturally significant?
- The Fukuromachi Dam is a gravity-type concrete sabo (erosion control) dam built in 1929 in the aftermath of the 1923 Great Kantō Earthquake. It was registered as a nationally designated tangible cultural property in 2004 for its contribution to Japan's national historical landscape. The dam is notable for protecting both downstream settlements and the ancient pilgrimage routes to sacred Mt. Ōyama.
- Can visitors see the Fukuromachi Dam in person?
- Unfortunately, the Fukuromachi Dam is located within a restricted access area and cannot be directly viewed by the public. However, the nearby Motodaki Dam, one of three companion heritage dams in the area, can be seen from the Kumoi Bridge along the Mt. Ōyama hiking trail.
- Why were sabo dams built in the Ōyama area?
- The 1923 Great Kantō Earthquake caused massive landslides across the Tanzawa mountains, destabilizing roughly 6,000 hectares of terrain. The resulting debris threatened downstream communities and infrastructure. Kanagawa Prefecture began constructing sabo dams from 1927 onward to prevent sediment disasters, and the Fukuromachi Dam was completed in 1929 as part of this effort.
- How do I get to the Mt. Ōyama area?
- From Isehara Station on the Odakyu Line, take the Kanagawa Chūō Kōtsū bus bound for "Ōyama Cable" (approximately 30 minutes). From the bus terminus, walk about 15 minutes through the Koma Sandō shopping street to reach the cable car station. By car, the Shin-Tōmei Expressway Isehara-Ōyama Interchange provides direct access.
- What other cultural properties are in the Isehara sabo dam group?
- The Fukuromachi Dam is one of three registered tangible cultural property dams in Isehara City: the Hachidan Dam (37m long, 11m high), the Motodaki Dam (25m long, 4.3m high), and the Fukuromachi Dam itself (24m long, 6m high). Together, they represent the early Shōwa-era sabo engineering heritage of the region.
Basic Information
| Name | Fukuromachi Dam (袋町堰堤) |
|---|---|
| Reading | Fukuromachi Entei |
| Designation | Nationally Registered Tangible Cultural Property (Building) |
| Category | Civil Engineering Structure (Erosion Control / Sabo) |
| Registration Number | 14-0089 |
| Year Built | 1929 (Shōwa 4) |
| Registration Date | July 23, 2004 |
| Structure | Gravity-type rubble masonry concrete dam |
| Dimensions | Dam length: 24m, Dam height: 6.0m |
| Quantity | 1 structure |
| Location | Ōyama, Isehara City, Kanagawa Prefecture |
| Owner | Kanagawa Prefecture |
| Registration Criteria | Contributes to the national historical landscape |
References
- 袋町堰堤 - 文化遺産オンライン
- https://bunka.nii.ac.jp/heritages/detail/188950
- 国指定文化財等データベース - 袋町堰堤
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00004220
- 八段滝堰堤・袋町堰堤・元滝堰堤 - 伊勢原市
- https://www.city.isehara.kanagawa.jp/bunkazai/docs/2013121600064/
- 砂防事業 - 神奈川県ホームページ
- https://www.pref.kanagawa.jp/docs/rt3/cnt/f645/sabo.html
- 不透過型砂防堰堤の整備事例 - 神奈川県ホームページ
- https://www.pref.kanagawa.jp/docs/vd8/kawa2/20231130/ennteishoukai.html
Last verified: 2026.04.19