Kosi River

Koshi
Nepali: कोशी, koshī, Hindi: कोसी, kosī
View of Koshi Bridge and Koshi River from Saptari, Nepal
Map showing Koshi Tributaries
Location
CountryChina, Nepal, India
StateTibet Autonomous Region, Koshi province, Bihar
CitiesSaptari, Sunsari, Supaul, Katihar, Bhagalpur
Physical characteristics
SourceSun Kosi, Arun and Tamur Rivers form Saptakoshi
 • locationTriveni, Nepal
MouthGanges
Length729 km (453 mi)
Basin size74,500 km2 (28,800 sq mi)
Discharge 
 • average2,500 m3/s (88,000 cu ft/s)

The Kosi or Koshi is a transboundary river which flows through China, Nepal and India. It drains the northern slopes of the Himalayas in Tibet and the southern slopes in Nepal. From a major confluence of tributaries north of the Chatra Gorge onwards, the Kosi River is also known as the Saptakoshi (Nepali: सप्तकोशी, saptakoshī) for its seven upper tributaries. These include the Tamur River originating from the Kanchenjunga area in the east and Arun River and the Sun Kosi from Tibet. The Sun Koshi's tributaries from east to west are the Dudh Koshi, Likhu Khola, Tamakoshi River, Bhote Koshi and Indravati. The Saptakoshi crosses into northern Bihar, India where it branches into distributaries before joining the Ganges near Kursela in Katihar district.[1] The Kosi is the third-largest tributary of the Ganges by water discharge after the Ghaghara and the Yamuna.[2]

The Kosi is 720 km (450 mi) long and drains an area of about 74,500 km2 (28,800 sq mi) in Tibet, Nepal and Bihar.[3][4] In the past, several authors proposed that the river has shifted its course by more than 133 km (83 mi) from east to west during the last 200 years. But a review of 28 historical maps dating 1760 to 1960 revealed a slight eastward shift for a long duration, and that the shift was random and oscillating in nature.[5]

The river basin is surrounded by ridges which separate the Kosi 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 12 distinct channels, all with shifting courses due to flooding.[6][7] Kamalā and Bāgmati (Kareh) are the major tributaries of Kosi River in India, besides minor tributaries such as Bhutahi Balān.[8][9]

Its unstable nature has been attributed to the power it can build up as it passes through the steep and narrow Chatra Gorge in Nepal.[10] During the monsoon season, It picks up a heavy silt load, which it redeposits at times, causing it to change its channel. This leads to flooding in India with extreme effects.[11] Fishing is an important enterprise on the river but fishing resources are being depleted and youth are leaving for other areas of work.[12]

  1. ^ Sharma, U. P. (1996). "Ecology of the Koshi river in Nepal-India (north Bihar): a typical river ecosystem". In Jha, P. K.; Ghimire, G. P. S.; Karmacharya, S. B.; Baral, S. R.; Lacoul, P. (eds.). Environment and biodiversity in the context of South Asia. Proceedings of the Regional Conference on Environment and Biodiversity, March 7–9, 1994, Kathmandu. Kathmandu: Ecological Society. pp. 92–99.
  2. ^ Jain, Sharad K.; Agarwal, Pushpendra K.; Singh, Vijay P. (16 May 2007). Hydrology and Water Resources of India. Springer Science & Business Media. ISBN 978-1-4020-5180-7.
  3. ^ "Kosi Basin". Water Resources Information system of India. Archived from the original on 1 June 2016. Retrieved 7 April 2016.
  4. ^ Nayak, J. (1996). Sediment management of the Kosi River basin in Nepal. In: Walling, D. E. and B. W. Webb (eds.) Erosion and Sediment Yield: Global and Regional Perspectives. Proceedings of the Exeter Symposium July 1996. IAHS Publishing no. 236. Pp. 583–586.
  5. ^ Chakraborty, T.; Kar, R.; Ghosh, P.; Basu, S. (2010). "Kosi megafan: historical records, geomorphology and the recent avulsion of the Kosi River". Quaternary International. 227 (2): 143–160.
  6. ^ Rao, K. L. (1975). India's Water Wealth. Orient Longman Ltd., Hyderabad, New Delhi.
  7. ^ Verghese, B. G. (1993) "Waters of Hope: Integrated Water Resource Development and Regional Cooperation within the Himalayan-Ganga-Brahmaputra-Barak Basin". Centre for Policy Research, New Delhi and Oxford. IBH Publishing Co., New Delhi.
  8. ^ Kosi River at the Encyclopædia Britannica
  9. ^ "Kosi River, Bihar, India". San Diego State University. Retrieved 9 March 2019.
  10. ^ "Anatomy of a flood: The case of Kosi in 2008 | India Water Portal". www.indiawaterportal.org. Retrieved 4 June 2022.
  11. ^ Bapalu, G. V. & Sinha, R. (2005). "GIS in Flood Hazard Mapping: a case study of Kosi River Basin, India" (PDF). GIS Development Weekly. 1 (13): 1–6. Archived from the original (PDF) on 5 December 2013.
  12. ^ Ranjit, R. (2002). The current status of capture fishery in the upper Sunkoshi River (Report). Technical Paper. FAO Fisheries and Aquaculture Department. pp. 247–256.