Saptakoshi River

Saptakoshi River

The Kosi River (Hindi: कोसी नदी) or Koshi (Nepali: कोशी नदी)—also Saptakoshi (Nepali: सप्तकोशी), is a trans-boundary river flowing through Nepal and India, known for its seven Himalayan tributaries. Some of the rivers of the Koshi system, such as the Arun, the Sun Kosi and the Bhote Koshi, originate in the Tibet Autonomous Region of China. It is one of the largest tributaries of the Ganges.

Along with its tributaries, the river drains 29,400 km2 (11,400 sq mi) in China (mainly the upper Arun basin north of the Mount Everest region), 30,700 km2 (11,900 sq mi) in Nepal (the eastern third of the country), and 9,200 km2 (3,600 sq mi) in India.

The river basin is surrounded by ridges which separate it from the Yarlung Tsangpo River in the north, the Gandaki in the west and the Mahananda in the east. The river is joined by major tributaries in the Mahabharat Range approximately 48 km (30 mi) north of the Indo-Nepal border. Below the Siwaliks, the river has built up a megafan some 15,000 km2 (5,800 sq mi) in extent, breaking into more than twelve distinct channels, all with shifting courses due to flooding. Kamlā, Bāghmati (Kareh) and Budhi Gandak are major tributaries of Koshi in India, besides minor tributaries such as Bhutahi Balān.

Over the last 250 years, the Kosi River has shifted its course over 120 km (75 mi) from east to west. Its unstable nature has been attributed to the heavy silt it carries during the monsoon season and flooding in India has extreme effects. The Kosi River (The Sorrow of Bihar) is one of two major tributaries and the other river, the Gandak, drains the plains of north Bihar, India's most flood-prone area. Fishing is an important enterprise on the river but fishing resources are being depleted and youth are leaving for other areas of work.