Tambara Dam is a hydroelectric power dam built on the Hotchi River, part of the Tone River system, in Tambara, Kamihocchi-cho, Numata City, Gunma Prefecture. It is currently operated and managed by TEPCO Renewable Power and serves as an important energy facility within the Tone River system.
Located in the high-altitude Tambara Plateau and surrounded by abundant natural beauty, the dam serves not only as a major power-generation facility but also as a scenic destination for visitors.
Tambara Dam is a 116.0-meter-high central-core rockfill dam. Construction began in 1973 and was completed in 1981.
At the time of its construction, the importance of hydroelectric power was being reassessed in Japan following the oil crisis. The dam was developed as part of a major national energy project intended to help provide a stable supply of electricity.
One of the dam’s notable features is its earthquake-resistant design, which was adapted to the area’s asymmetrical terrain. The structure represents a significant engineering achievement, built to overcome the challenging geographical conditions of this mountainous region.
When the dam was originally completed, the name “玉原” was pronounced “Tamahara.” As tourism development in the surrounding area progressed, the pronunciation “Tambara” became widely established. On February 1, 2004, the official name was changed to Tambara Dam.
Today, “Tambara” is also the name commonly used for the highland resort and other attractions in the surrounding area.
Tambara Dam functions as the upper reservoir of a pumped-storage hydroelectric power system. The dam’s reservoir, Lake Tambara, serves as the upper reservoir, while Fujiwara Dam and its reservoir, Lake Fujiwara, managed by the Ministry of Land, Infrastructure, Transport and Tourism, serve as the lower reservoir.
Tambara Power Station has an authorized generating capacity of 1,200,000 kW, making it one of the largest hydroelectric power facilities in the Tone River system.
Pumped-storage hydroelectric power works by pumping water up to the upper reservoir when electricity demand is low. When demand increases, the stored water is released downward to generate electricity. This system helps balance electricity supply and demand and contributes to a stable power supply.
The construction of Tambara Dam involved extensive coordination to address its potential impact on the surrounding environment and local industries.
In particular, concerns were raised about the effect on trout farming, which was an important industry along the Hotchi River. As a result, water from the Hotchi River was not used for power generation; instead, the river was diverted through a tunnel to reduce the impact on the local fish-farming industry.
Environmental considerations were also incorporated to protect the natural environment of the Tambara Wetland upstream. The dam was designed with a lower height than originally planned in order to reduce its impact on the wetland ecosystem.
Lake Tambara, formed by the dam, offers beautiful scenery that changes with the seasons.
From spring through summer, the surrounding highlands are filled with fresh greenery and pleasant mountain scenery. In autumn, the mountains surrounding the lake are transformed by brilliant foliage.
The dam embankment is open to visitors during the daytime, allowing them to walk from the left bank to the right bank and enjoy the scenery along the way.
On clear days, visitors can experience the striking harmony between the enormous dam structure and the surrounding mountains beneath the plateau’s crisp, clear air.
Tambara Dam is located within Tambara Plateau, a popular forest resort surrounded by rich natural environments. The surrounding area includes Tambara Wetland and extensive beech forests, which provide habitat for the Japanese serow, a nationally designated Special Natural Monument of Japan.
During summer, Tambara Lavender Park opens on the plateau, with approximately 50,000 lavender plants blooming across the highland landscape.
At an elevation of approximately 1,300 meters, Tambara remains cool even during summer, with an average temperature of around 20°C. Its pleasant climate makes it a popular summer retreat for visitors from the Tokyo metropolitan area.
During winter, the area operates as Tambara Ski Park, offering visitors the opportunity to enjoy high-quality powder snow.
Many of the ski runs are designed for beginners and intermediate skiers, making the resort suitable for families and first-time skiers and snowboarders.
After enjoying skiing or snowboarding, visitors can also take in the peaceful winter scenery around Lake Tambara.
The area around Tambara Dam lies adjacent to Joshin’etsukogen National Park and is surrounded by a variety of natural and recreational attractions. The Minakami Onsenkyo hot spring area and central Numata are also relatively accessible, making the region a convenient base for sightseeing.
Visitors can enjoy the area in many different ways, including nature walks, photography, and scenic drives. The combination of the highland landscape, forests, lake, and impressive dam makes it an appealing destination for those interested in both nature and infrastructure.
Tambara Dam plays an important role as one of the Kanto region’s major pumped-storage hydroelectric facilities while also forming part of the scenic landscape of Tambara Plateau.
Understanding the history behind its construction and the efforts made to balance hydroelectric power generation with environmental conservation can add another dimension to a visit.
Along with the changing scenery of the four seasons, the impressive scale of Tambara Dam offers visitors an opportunity to experience both the power of nature and the remarkable infrastructure that supports Japan’s energy supply.