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| Koshi | |
|---|---|
 | |
 Map showing Koshi Tributaries | |
| Location | |
| Country | China,Nepal,India |
| State | Tibet Autonomous Region,Koshi province,Bihar |
| Cities | Saptari,Sunsari,Supaul,Katihar,Bhagalpur |
| Physical characteristics | |
| Source | Sun Kosi,Arun andTamur Rivers form Saptakoshi |
| • location | Triveni,Nepal |
| Mouth | Ganges |
| Length | 729 km (453 mi) |
| Basin size | 74,500 km2 (28,800 sq mi) |
| Discharge | |
| • average | 2,500 m3/s (88,000 cu ft/s) |
TheKosi orKoshi is atransboundary river which flows throughChina,Nepal andIndia. It drains the northern slopes of theHimalayas in Tibet and the southern slopes in Nepal. From a major confluence of tributaries north of theChatra Gorge onwards, the Kosi River is also known as theSaptakoshi (Nepali:सप्तकोशी,saptakoshī) for its seven upper tributaries. These include theTamur River originating from theKanchenjunga area in the east andArun River and theSun Kosi from Tibet. The Sun Koshi's tributaries from east to west are theDudh Koshi,Likhu Khola,Tamakoshi River,Bhote Koshi andIndravati. The Saptakoshi crosses into northernBihar, India where it branches intodistributaries before joining theGanges nearKursela inKatihar district.[1] The Kosi is the third-largest tributary of the Ganges by water discharge after theGhaghara and theYamuna.[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 theYarlung Tsangpo River in the north, theGandaki in the west and theMahananda in the east. The river is joined by major tributaries in theMahabharat Range approximately 48 km (30 mi) north of the Indo-Nepal border. Below theSiwaliks, the river has built up amegafan 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 andBāgmati (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 narrowChatra Gorge in Nepal.[10] During themonsoon 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]
The Kosi River catchment covers sixgeological and climatic belts varying in altitude from above 8,000 m (26,000 ft) to 95 m (312 ft) comprising theTibetan plateau, the Himalayas, the Himalayan mid-hill belt, theMahabharat Range, theSiwalik Hills and theTerai. The Dudh-Koshi sub-basin alone consists of 36glaciers and 296glacier lakes.[13]The Kosi River basin borders theTsangpo River basin in the north, theMahananda River basin in the east, theGanges Basin in the south and theGandaki River basin in the west.[14] The eight tributaries of the basin upstream theChatra Gorge include from east to west:[15]
The three major tributaries meet atTriveni, from where they are calledSapta Koshi meaningSeven Rivers. After flowing through the Chatra Gorge the Sapta Koshi is controlled by theKoshi Barrage before it drains into theGangetic plain.[15]
The reason for such a large, deep gorge is that the riveris antecedent to the Himalayas, meaning that it had existed before them and hasentrenched itself since they started rising.
Peaks located in the basin includeMount Everest,Kangchenjunga,Lhotse,Makalu,Cho Oyu andShishapangma.[16] TheBagmati river sub-basin forms the south-western portion of the overall Kosi basin.
The Kosialluvial fan is one of the largest in the world. It shows evidence of lateral channel shifting exceeding 120 km (75 mi) during the past 250 years, via at least twelve major channels. The river, which flowed nearPurnea in the 18th century, now flows west ofSaharsa. A satellite image shows old channels with a confluence before 1731 with the Mahananda River north ofLava.[17]
The Kosi River is known as the "Sorrow of Bihar" as the annual floods affect about 21,000 km2 (8,100 sq mi) of fertile agricultural lands thereby disturbing the rural economy.[1]It has an average water flow (discharge) of 2,166 cubic metres per second (76,500 cu ft/s).[18]
On 18 August 2008, the Kosi River picked up an old channel it had abandoned over 100 years previously near the border with Nepal and India. Approximately 2.7 million people were affected as the river broke its embankment at Kusaha inNepal, submerging several districts of Nepal and India. 95% of the Kosi's water flowed through the new course.[19] The worst affected districts includedSupaul,Araria,Saharsa,Madhepura,Purnia,Katihar, parts ofKhagaria and northern parts ofBhagalpur, as well as adjoining regions of Nepal. Relief work was carried out withIndian Air Forcehelicopters by dropping relief materials from Purnia in the worst hit districts where nearly two million persons were trapped.[20]The magnitude of deaths or destruction were hard to estimate, as the affected areas were inaccessible. 150 people were reported washed away in a single incident.[21] Another news item stated that 42 people had died.[22]
TheGovernment of Bihar convened a technical committee, headed by a retired engineer-in-chief of the water resource department to supervise the restoration work and close the breach in the East Kosi afflux embankment.[22] Indian authorities worked to prevent widening of the breach, and channels were to be dug to direct the water back to the main river bed.[23]
The fury of the Kosi River left at least 2.5 million people marooned in eight districts and inundated 400 sq mi (1,000 km2). The prime Minister of India declared it a national calamity. The Indian Army,National Disaster Response Force (NDRF) and non-government organizations operated the biggest flood rescue operation in India in more than 50 years.[24][25]
The National Flood Control Policy in 1954 (following the disastrous floods of 1954 in a large part of the Kosi river basin) planned to control floods through a series of dams, embankments and river training works. The Kosi project was thus conceptualized (based on investigations between 1946 and 1955), in three continuous interlinked stages
This was followed by the Kosi Agreement between Nepal and India signed on 25 April 1954 and revised on 19 December 1966 to address Nepal's concerns. Further letters of Exchange to the Agreement between the two countries identified additional schemes for providing benefits of irrigation. While the first two parts of the plan were implemented by theGovernment of India, the Kosi High dam, the linchpin of the whole plan, for various political reasons has yet precluded any action for several years but has since been revived under a fresh agreement, in a modified form for further investigations and studies.[28]
Kosi Barrage, also called Bhimnagar Barrage, was built between 1959 and 1963 and straddles the Indo-Nepal border. It is an irrigation, flood control andhydropower generation project on the Kosi River built under a bilateral agreement between Nepal and India: the entire cost of the project was borne by India. The catchment area of the river is 61,788 km2 (23,856 sq mi) in Nepal at the barrage site. The highest peaks lie in its catchment. About 10% is snow-fed. The Eastern Canal and the Western Canal taking off from the barrage, were designed for a discharge capacity of 455 cubic metres per second (16,100 cu ft/s) to irrigate 6,125 square kilometres (1,514,000 acres) and 210 cubic metres per second (7,400 cu ft/s) to irrigate 3,566.1 square kilometres (881,200 acres), respectively. A hydropower plant has been built on the Eastern Canal, at a canal drop (3.6 km (2.2 mi) from the Kosi Barrage), to generate 20 MW. The Western Koshi Canal provides irrigation to 250 square kilometres (62,000 acres) in Nepal. A valuable bridge over the barrage opened up the east–west highway in the eastern sector of Nepal.[29]
An inundation canal taking off at Chatra, where the Kosi River debouches into the plains, has been built to irrigate a gross area of 860 km2 in Nepal. The project was renovated withIDA assistance after Nepal took over the project in 1976.[26]
The Koshi barrage, with earth dams across the river, as well as afflux bunds and embankments above and below the river, confines the river to flow within embankments. Embankments on both sides downstream of the barrage with a length of 246 km (153 mi) were constructed to check the westward movement of the river. The embankments have been kept far apart, about 12 to 16 km (9.9 mi), to serve as a silt trap.[26]
The governments of India and Nepal agreed to conduct joint investigations and other studies for the preparation of a detailed project report ofSapta Koshi High Dam Multipurpose Project andSun Koshi Storage-cum-Diversion Scheme to meet the objectives of both countries for development of hydropower, irrigation, flood control and management and navigation. As currently outlined, the dam would displace approximately 10,000 people.[30]
Envisaged are a 269-meter (883 ft) high concrete or rock-filled dam, a barrage, and two canals. The dam is on the Sapta Koshi River with an underground powerhouse, producing 3,000 MW at 50% load factor. The barrage is planned for the Sapta Koshi about 8 km (5.0 mi) downstream of Sapta Koshi High Dam to re-regulate the diverted water. The Eastern Chhatra Canal and Western Chhatra Canal, off-take from the barrage site to provide water for irrigation both in Nepal and India and navigation through Koshi up to Kursela and also in the reservoir of Sapta Koshi dam.[28]
A power canal existing Kosi barrage at Hanuman Nagar is proposed for conveying water for irrigation from the Eastern Chatra Canal and also water that may be required downstream for navigation. To utilize the head available between Chatra and Hanuman Nagar barrages for power generation, three canal power houses, each of 100 MW installed capacity are proposed on the power canal.
Extra storage capacity of Sapta Koshi High Dam would be provided to moderate downstream flooding.Chatra Canal System would provide irrigation to large areas in Nepal and India, particularly in Bihar.A Joint Project Office (JPO) has been set up in Nepal for investigation of the project.
Nepal has a total estimated potential of 83,290 MW with economically exploitable potential of 42,140 MW. The Kosi River basin contributes 22,350 MW of this potential including 360 MW from small schemes and 18750 MW from major schemes. The economically exploitable potential is assessed as 10,860 MW (includes the Sapta Koshi Multipurpose Project [3300MW] mentioned above).[31]
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Commercial river rafting, also known aswhitewater rafting, andcanyoning is available on the Sun Koshi river and tributaries. Sun Koshi has challengingrapid grades of class 4–5.[32]
Mahseer is widely distributed in Himalayan rivers up to 1,650 m (5,410 ft) altitude and also inhabits the Kosi River and its tributaries.[33]
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The Kosi was also called Kausika inRigveda. It is a major tributary of the Ganges. One major tributary of the Kosi is the Arun, much of whose course is in Tibet. This river is mentioned in the epic 'Mahabharata' as Kausiki, named after the sageViśvāmitra who was a descendant of the sage Kusika and is said to have attained the status of 'Rishi' on the banks of the river, where he had his hermitage.
The Kosi is associated with many ancient spiritual stories. It is mentioned in the Bal Kand section of Valmiki Ramayana as the Kausiki who is the form assumed by Satyavati after her death. Satyavati was the elder sister of Viswamitra, descendants of Kushak dynasty. In theMarkandeya Purana, the Kosi is described as the primal force. Due to the violent nature of the Kosi during monsoon season, legend says that Parvati, the wife ofShiva, after defeating the demonDurg, became known as the warrior goddess Durga who transformed into Kaushiki. In Ramayana, the river Ganges is depicted as her elder sister.
According toMahabharata epic, the God of death took the form of a woman and resides on the banks of the river to limit population growth. Kosi resonates with the folklore of Mithila. The most important depictions of Kosi folklore are Kosi as a virgin absolutely care free and full of energy and as a frustrated wife of old hermit Richeek wandering in theHimalayas. Kosi is also invoked as the mother – 'Kosi Ma'. These images capture the contradiction that is inherent in the Kosi River as a source of life and death, prosperity and destruction; a mother and an enchanting virgin.
It is also the lifeline of theMithila region, today spread over more than half of India's state of Bihar, and is the subject of legend and folklore of the region.
In Nepal twoprotected areas are located in the Koshi River basin.[34]
TheSagarmatha National Park encompasses the upper catchments of the Dudh Koshi River system. The park covers an area of 1,148 km2 (443 sq mi) and ranges in elevation from 2,845 m (9,334 ft) to 8,848 m (29,029 ft) at the summit ofMount Everest. Established in 1976 the park was declared aUNESCO World Heritage Site in 1979. The landscape in the park is rugged consisting of mountain peaks,glaciers, rivers, lakes, forests, alpine scrubs and meadows. The forests comprise stands ofoak,blue pine,fir,birch,juniper andrhododendron. The park provides habitat forsnow leopards,red pandas,musk deer,Himalayan tahrs, and 208 bird species includingimpeyan pheasant,bearded vulture,snow cock, and theyellow-billed chough.[34]
About 3500Sherpa people live in villages and seasonal settlements situated along the main tourist trails. Tourism to the region began in the early 1960s. In 2003, about 19,000 tourists arrived in the area.[35]
TheKoshi Tappu Wildlife Reserve is situated in the flood plains of the Saptkoshi River in the easternTerai. It covers an area of 175 km2 (68 sq mi) comprising grasslands andkhair–sissooriverine forests. It was established in 1976 and was declared aRamsar site in 1987. The reserve provides habitat forhog deer,spotted deer,wild boar,blue bull,gaur,smooth-coated otter,jackal, 485 bird species including 114water bird species, 200 fish species, 24reptile and 11amphibian species.[34] The last surviving population ofwild water buffalo in Nepal is found in the reserve, as well asGangetic dolphin,swamp francolin andrufous-vented prinia.[36] A small population of thecritically endangeredBengal florican is present along the Koshi River.[37] There are also records ofwhite-throated bush chat andFinn's weaver. Thebristled grassbird breeds in the reserve.[38] The reserve together with theKoshi Barrage was identified as one of 27Important Bird Areas of Nepal.[39]
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