One of Japan’s Rare Buttress Dams
The most distinctive feature of Marunuma Dam is its unusual buttress dam design. In this type of structure, a water-retaining wall is supported by a series of reinforced structures known as buttresses. Only eight buttress dams were constructed in Japan during the early Showa period, and just six of them remain today. Among the surviving examples, Marunuma Dam is the largest.
This construction method had the advantage of reducing the amount of concrete required. However, it also demanded advanced construction techniques and had disadvantages including vulnerability to earthquakes and deterioration of exposed surfaces. As a result, the design gradually fell out of use.
Because of its rarity, Marunuma Dam is an important site for understanding the history of dam construction and modern civil engineering in Japan.
A Historic Hydroelectric Dam in Nikko National Park
Marunuma Dam was completed in 1928 by Tokyo Electric Light Company, the predecessor of today’s electric power companies. The project was designed to increase the storage capacity of the naturally formed Lake Marunuma and secure a stable supply of water for hydroelectric power generation.
Water released from the dam is conveyed downstream to Ichinose Power Station, where it is used to generate hydroelectric power.
Over the following decades, the management of the facility changed several times as Japan underwent major changes in its electricity industry. Management passed from Tokyo Electric Light Company to Nippon Electric Generation and Transmission Company, then to Tokyo Electric Power Company, and eventually to today’s TEPCO Renewable Power.
Despite these changes, Marunuma Dam has continued to operate for nearly a century, quietly contributing to Japan’s electricity supply.
Recognized as an Important Cultural Property of Japan
In recognition of its rarity and historical importance, Marunuma Dam was designated a National Important Cultural Property in 2003 under the name Marunuma Weir. It was the first dam built exclusively for hydroelectric power generation in Japan to receive this designation.
All of Japan’s surviving buttress dams have also been selected as Heritage of Civil Engineering Sites by the Japan Society of Civil Engineers.
The dam has been carefully repaired and maintained while respecting the original design and appearance. The fact that it continues to function in the harsh climate of this cold, snowy mountain region while retaining much of its original character makes it a remarkable example of Japan’s early modern civil engineering technology.
A Scenic Attraction in Harmony with Nature
Marunuma Dam is located within Nikko National Park. The surrounding area features beautiful lakes such as Lake Marunuma and Lake Suganuma, as well as spectacular mountain scenery extending toward Konsei Pass and the Oze region.
The dam is situated along National Route 120, making it possible to include a visit to Marunuma Dam in a sightseeing drive through Oku-Nikko and Katashina Village.
Visitors cannot enter the interior of the dam, but the exterior can be viewed from nearby. The distinctive buttress structure supporting the dam body is rarely seen elsewhere and makes Marunuma Dam an especially interesting destination for photography and civil-engineering enthusiasts.
Dam Cards and Other Ways to Enjoy the Visit
Marunuma Dam is also associated with Japan’s popular Dam Card program. These collectible cards introduce individual dams and their features, and collecting them has become a unique pastime for some visitors.
A special premium Dam Card is also available exclusively to visitors who stay overnight in Katashina Village, allowing the dam visit to be combined with a stay in the local area.
A Unique Meeting Point of History, Technology and Nature
Marunuma Dam is much more than a hydroelectric facility. It is a symbol of the civil engineering technology that supported Japan’s modernization and an important cultural heritage site that exists in harmony with its natural surroundings.
The elegant structure, which retains the appearance and atmosphere of the early Showa period, contrasts beautifully with the surrounding mountains and forests. Together, the historic dam and magnificent natural landscape create a peaceful and memorable sightseeing experience.
When visiting Katashina Village, consider taking time to walk along the shores of Lake Marunuma and admire this historic dam from nearby. After nearly a century of operation, Marunuma Dam continues to stand with quiet strength, connecting Japan’s technological past with the present and offering visitors a fascinating glimpse into the country’s modern civil engineering heritage.