|
The Koshi or Kosi River ((ネパール語:कोशी नदी), , ) drains the northern slopes of the Himalayas in the Tibet Autonomous Region and the southern slopes in Nepal. From a major confluence of tributaries north of the Chatra Gorge onwards, the Koshi River is also known as Saptakoshi ((ネパール語:सप्तकोशी), ) for its seven upper tributaries. These include the Tamur Koshi originating from the Kanchenjunga area in the east, Arun River from Tibet and Sun Koshi from the Gosainthan area farther west. The Sun Koshi's tributaries from east to west are Dudh Koshi, Bhote Koshi, Tamba Koshi and Indravati Koshi. The Saptakoshi crosses into northern Bihar where it branches into distributaries before joining the Ganges near Kursela in Katihar district.〔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. Ecological Society, Kathmandu. Pp 92–99.〕 The Saptakoshi is long and drains an area of about in Tibet, Nepal and Bihar.〔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.〕 In the past, several authors proposed that the river has shifted its course for more than 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 shifting was random and oscillating in nature.〔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.〕 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 north of the Indo-Nepal border. Below the Siwaliks, the river has built up a megafan some in extent, breaking into more than twelve distinct channels, all with shifting courses due to flooding.〔Rao, K.L. (1975). ''India's Water Wealth''. Orient Longman Ltd., Hyderabad, New Delhi.〕〔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.〕 Kamalā, Bāgmati (Kareh) and Budhi Gandak are major tributaries of Koshi in India, besides minor tributaries such as Bhutahi Balān.〔(【引用サイトリンク】title=Koshi River, Bihar, India )〕 Its unstable nature has been attributed to the heavy silt it carries during the monsoon season and flooding in India has extreme effects. Fishing is an important enterprise on the river but fishing resources are being depleted and youth are leaving for other areas of work. ==Geography== The Kosi River catchment covers six geological and climatic belts varying in altitude from above to comprising the Tibetan plateau, the Himalayas, the Himalayan mid-hill belt, the Mahabharat Range, the Siwalik Hills and the Terai. The Dudh-Kosi sub-basin alone consists of 36 glaciers and 296 glacier lakes.〔Bajracharya, S. R., Mool, P. K., Shrestha, B. R. (2007). Impact of climate change on Himalayan glaciers and glacial lakes: case studies on GLOF and associated hazards in Nepal and Bhutan. International Centre for Integrated Mountain Development (ICIMOD).〕 The Kosi River basin borders the Tsangpo River basin in the north, the Mahananda River basin in the east, the Ganges Basin in the south and the Gandaki River basin in the west. The eight tributaries of the basin upstream the Chatra Gorge include from east to west:〔Nepal, S. (2012). ''Evaluating upstream downstream linkages of Hydrological Dynamics in the Himalayan Region''. Dissertation, Faculty of Chemical and Earth Sciences of the Friedrich-Schiller-University Jena.〕 * Tamur River with an area of in eastern Nepal; * Arun River with an area of , most of which is in Tibet; * Sun Kosi with an area of in Nepal and its northern tributaries Dudh Kosi, Likhu Khola, Tama Koshi, Bhote Koshi and Indravati. The three major tributaries meet at Triveni, from where they are called ''Sapta Kosi'' meaning ''Seven Rivers''. After flowing through the Chatra Gorge the Sapta Kosi is controlled by the Koshi Barrage before it drains into the Gangetic plain.〔 Peaks located in the basin include Mount Everest, Kangchenjunga, Lhotse, Makalu, Cho Oyu and Shishapangma.〔Shijin, W., & Tao, Z. (2014). Spatial change detection of glacial lakes in the Koshi River Basin, the Central Himalayas. Environmental Earth Sciences 72(11): 4381–4391.〕 The Bagmati river sub-basin forms the south-western portion of the overall Koshi basin. The Dudh Kosi joins the Sun Kosi near the Nepalese village of Harkapur. At in Nepal it emerges from the mountains and becomes the ''Koshi''. After flowing another it crosses into Bihar, India, near Bhimnagar and after another joins the Ganges near Kursela. The Kosi alluvial fan is one of the largest in the world, and extends from Barāhkṣetra across Nepalese territory, covering northeast Bihar and eastern Mithila to the Ganges, long and wide. It shows evidence of lateral channel shifting exceeding during the past 250 years, via at least twelve major channels. The river, which flowed near Purnea in the 18th century, now flows west of Saharsa. A satellite image shows old channels with a confluence before 1731 with the Mahananda River north of Lava. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Koshi River」の詳細全文を読む スポンサード リンク
|