Kami-Shiiba Dam is a hydroelectric dam built on the uppermost reaches of the Mimi River, a Class B river in Shiiba Village, Higashiusuki District, Miyazaki Prefecture. Managed by Kyushu Electric Power, it is an arch-shaped concrete dam standing 111.0 meters high. As Japan’s first large-scale arch dam in the 100-meter class, it had a major influence on the development of civil engineering technology in Japan.
The dam forms the core of a group of hydroelectric power stations in the Mimi River system. The adjoining Kami-Shiiba Power Station has a maximum generating capacity of 90,000 kilowatts, with electricity transmitted to the Kitakyushu Industrial Zone.
The reservoir created by the dam is called Lake Hyuga-Shiiba. Its name was given by the novelist Eiji Yoshikawa. In 2005, following a recommendation from Shiiba Village, the lake was selected for the One Hundred Selected Dam Lakes of Japan. The area is also part of Kyushu Chuo Sanchi Quasi-National Park and is one of the major sightseeing destinations in northern Miyazaki Prefecture. In 2019, the dam was selected as a Civil Engineering Heritage Site by the Japan Society of Civil Engineers in recognition of its historical value as a large-scale arch dam.
Completed in 1955, Kami-Shiiba Dam was Japan’s first large-scale arch-shaped concrete dam. Its structure is approximately 110 meters high and 341 meters long, with a total reservoir capacity of 91.55 million cubic meters.
The dam plays an important role in supplying electricity to Kyushu through hydroelectric power generation. During Japan’s postwar reconstruction period, securing electricity for the Kitakyushu Industrial Zone was an urgent priority. Kami-Shiiba Dam helped meet this demand and contributed significantly to the region’s economic development.
Lake Hyuga-Shiiba, the artificial lake formed by the dam, is also a popular sightseeing destination. Its scenery changes with the seasons, offering visitors beautiful views throughout the year. Near the dam is a viewpoint called Megami-zo Park, from which visitors can enjoy expansive views of both the dam and the lake.
There are several popular places to visit around Kami-Shiiba Dam. One of the highlights is Megami-zo Park, which overlooks the dam and offers impressive views of the surrounding landscape.
The park also contains a memorial tower commemorating the 105 people who lost their lives in connection with the construction of the dam. The monument provides an opportunity to reflect on the human cost of this major engineering project.
The autumn foliage season is particularly beautiful around the dam. In addition, a special sightseeing water-release event is held in November, when visitors can appreciate the powerful spectacle of water being discharged from the dam. These seasonal attractions offer a striking combination of natural scenery and engineering.
Megami-zo Park is an excellent place to appreciate the impressive scale of Kami-Shiiba Dam. Located on elevated ground, it offers a panoramic view of the dam and Lake Hyuga-Shiiba.
The lake and surrounding natural landscape display different scenery throughout the year. During the autumn foliage season, colorful leaves are reflected on the surface of the lake, creating a particularly beautiful scene. The observation point is popular not only with dam enthusiasts but also with people who enjoy nature and scenic photography.
One unusual experience at Kami-Shiiba Dam is the opportunity to drive across the top of the dam. The roadway is also open to bicycles, allowing visitors to enjoy cycling while feeling the refreshing breeze and taking in the surrounding scenery.
For visitors arriving by car or bicycle, crossing the dam itself is a memorable part of the trip. It is also recommended to stop along the way at suitable places to take photographs and appreciate the impressive structure.
The construction of Kami-Shiiba Dam was a major project in the history of Japanese civil engineering. A key development leading to its construction was the completion of Tsukabara Dam in 1938. This earlier dam opened the way for hydroelectric power development along the Mimi River and was the tallest dam in Japan at the time. Its construction technology had a major influence on subsequent dam projects.
The Mimi River region was historically difficult to access, even by the standards of Kyushu. The road connecting Kamishiiba Village and Hyuga City was not completed until 1933. The opening of this road helped accelerate plans to develop the river’s potential for hydroelectric power generation.
Initially, water rights along the Mimi River were acquired by the Sumitomo conglomerate, with the aim of supplying electricity to the industrial areas of northern Kyushu. The rights were eventually taken over by Kyushu Transmission and Distribution, after which construction of power stations along the Mimi River moved forward in earnest.
Following World War II, rebuilding Japan’s industries became an urgent national priority. A stable electricity supply for the Kitakyushu Industrial Zone was essential, and plans for Kami-Shiiba Dam were revived.
Surveying at the present dam site began in 1946, and full-scale construction started in 1950. The project faced various difficulties, including the need for residents of Shiiba Village to relocate because of the dam’s construction. Despite these challenges, the dam was completed in 1955 as Japan’s first large-scale arch dam.
Kami-Shiiba Dam was the first dam in Japan to be built as a 100-meter-class arch-shaped concrete structure. At the time, large arch dams were already being constructed overseas, but this type of structure had not yet been adopted in Japan because of concerns about earthquake resistance and flood-control capacity.
However, the bedrock in the Mimi River basin consists of solid granite. After considering both economic efficiency and safety, engineers concluded that an arch dam was the most suitable design for the site.
Building an arch dam presented several technical challenges, particularly concerning earthquake resistance and the ability to handle floods. Japanese engineers addressed these issues through a number of innovative design solutions.
One important feature was the adoption of a ski-jump-type spillway. This design disperses the energy of water discharged during floods, reducing the impact on the dam itself.
The engineers also made use of the area’s strong bedrock and adopted a thick-arch dam design. This helped improve the structure’s safety against both earthquakes and water pressure.
Kami-Shiiba Dam continues to be operated by Kyushu Electric Power and fulfills both its role in electricity generation and its function as a sightseeing destination. It is a symbol of Shiiba Village, attracting visitors while remaining an important part of the region’s electricity supply infrastructure.
With its historical significance and continuing practical role, Kami-Shiiba Dam is expected to remain an important asset for regional development while contributing to the protection of the surrounding natural environment.