Tenryū River

The Tenryū River is the only river exiting Lake Suwa. It follows a generally southern course. The upper reaches of the river in the Ina Basin of Nagano Prefecture is a rich agricultural area. The river exits through a gap between the Kiso Mountains (Central Alps) and the Akaishi Mountains (Southern Alps), which forms the border between Shizuoka and Nagano Prefectures . This area is characterized by heavy rainfall (up to 3000 mm per year) and deep V-shaped valleys. Continuing south through Shizuoka Prefecture, the river drains a wide coastal plain noted for fruit and rice production. The city of Hamamatsu is near the river mouth at the Philippine Sea.

The Tenryū River is mentioned in Nara period records as the Violent Tenryū (暴れ天竜, Abare-Tenryū) for its fast, turbulent flow and its propensity to flood. The upper portion of the river (in Shinano Province) was referred to as the Tenryūgawa, whereas the lower portion (in Tōtōmi Province) was often referred to as the Aratama River (麁玉川, Aratama-gawa). In various entries in the national historical chronicle Shoku Nihongi, flooding of the river is mentioned in the years 710 CE and 765 CE. Records through the Heian period and Kamakura period are sparse, but from the Muromachi period, increasing efforts at flood control were made by various warlords and landholders along the river by construction of dikes, levees, and channels.

With the occupation of Hamamatsu Castle by Tokugawa Ieyasu, considerable efforts were made to increase the revenues of Tōtōmi Province through creation of new rice fields with irrigation from the Tenryū River. However, flooding remained a problem, including a great flood in 1674 which washed away many of the earthen works of previous centuries.

The Tenryū River

Hiroshige

The potential of the Tenryū River valley for hydroelectric power development was realized by the Meiji government at the start of the 20th century. The Tenryū River was characterized by a high volume of flow and a fast current. Its mountainous upper reaches and tributaries were areas of steep valleys and abundant rainfall, and were sparsely populated. However, the bulk of investment in hydroelectric power generation in the region was centered on the Ōi River, and it was not until the Taishō period that development began on the Tenryū River.

Private entrepreneur Fukuzawa Momosuke founded the Tenryūgawa Electric Power (天竜川電力, Tenryūgawa Denroku), which later became Yahagi Hydroelectric (矢作水力, Yahagi Suiroku) before it was nationalized into the pre-war government monopoly Japan Electric Generation and Transmission Company (日本発送電株式会社, Nippon Hassoden K.K.) in 1938. The first dam on the main stream of the Tenryu River, the Yasuoka Dam was completed in 1935. This was followed by the Iwakura Dam in 1938. The Hiraoka Dam was started in 1938, but completed until 1951 due to the start of World War II.

Tenryū river, upper reaches

After the end of World War II, the American occupation authorities ordered the dissolution of Nippon Hassoden, which was divided into regional power companies. Central Japan came under Chubu Electric Power, which inherited the various dams and projects on the Tenryū River, all of which were located in Nagano Prefecture. For develop of the hydroelectric potential of the river in Shizuoka Prefecture, the government turned to the Electric Power Development Company. The new company, in part through foreign aid loans from the United Nations, and with the use of new dam technologies completed the huge Sakuma Dam in the 1956, at the time the 10th largest in the world. Further dams were completed in the 1960s and 1970s until the completion of the Funagira Dam in 1976 brought development of the Tenryū River to a close.

The Tenryū River Valley is partially within the Tenryū-Okumikawa Quasi-National Park with the Tenryū-kyō gorges as a nationally designated nationally designated Place of Scenic Beauty in Iida, Nagano Prefecture, Japan.[1]

The Tenryū Hamanako Railroad Tenryū Hamanako Line runs along the lower reaches of the Tenryū River valley, whereas the Iida Line runs along the upper reaches of the river into upper Shizuoka and Nagano prefectures, with a stop at Sakuma Station near the namesake dam.

• Tenryū-class cruiser, led by Japanese cruiser Tenryū
• Japanese Alps

Wikimedia Commons has media related to Tenryu River.

• Ministry of Land, Infrastructure and Transport

34°38′54″N 137°47′27″E (mouth)