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The Kosi River -- called Koshi in Nepal ( ) as well as Saptakoshi for its seven Himalayanmarker tributaries -- is a transboundary river between Nepalmarker and Indiamarker, one of the largest tributaries of the Gangesmarker. The river, along with its tributaries, drains a total area of up to its confluence with the Ganges in India ( in Chinamarker, in Nepal and in India). The watershed also includes part of Tibet, such as the Mount Everestmarker region, and the eastern third of Nepal. The river basin is surrounded by the ridges separating it from the Yarlung Zangbo River in the north, the Gandaki in the west, the Mahanandamarker in the east, and by the Ganges in the south. The river is joined by major tributaries in the Mahabharat Rangemarker approximately north of the Indo-Nepal border. Below the outermost foothills (Siwaliks) the river has built up a megafan some 15,000 sq. km in extent, breaking into more than twelve distinct channels with shifting courses due to flooding. Kamlā, Bāghmati (Kareh) and Budhi Gandak are major tributaries of Koshi in India, besides minor tributaries like Bhutahi Balān.Over the last 250 years, the Kosi River has shifted its course over from east to west. and the unstable nature of the river is attributed to the heavy silt which it carries during the monsoon season. Flooding in India has extreme effects. India is second in the world after Bangladeshmarker in deaths due to flooding, accounting for one fifth of global flooding deaths. The Kosi River (The Sorrow of Bihar) is one of two major tributaries, the other river being Gandak, draining the plains of north Biharmarker, the most flood-prone area of India


Formerly Kauśiki (named after sage Viśvāmitra because Viśvāmitra is said to have attained the status of Vedic or Rishi on its banks; Viśvāmitra was descendant of sage Kuśika and was called Kauśika in Rigveda), in Nepalmarker and Bihar in northern India is a major tributary of the Gangesmarker (one major tributary of the Koshi is the Arun, a major part of whose course is in Tibet). This river is mentioned in the epic Mahabharata as Kauśiki. Seven Koshis join together to form the Saptakoshi River/Sapt Koshi which is popularly known as the Koshi.

It is also the lifeline of the Mithila region, today spread over more than half of India's state of Bihar, and parts of adjoining Nepal and it forms the basis of legend and folklore of the region; the legend of Mithila extends over many centuries. Mithila is also the name of a style of Hindu art created in the Mithila area.

Access to the basin

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From Katmandumarker, there is a road for some distance followed by trekking paths to Mt Everestmarker, which crosses four major tributaries of the Koshi. Namche Bazarmarker near Tibet border in Nepal (near southern base camp of Mt Everest) is the major tourist centre in the mountainous part of the Koshi belt. Birātnagar in Nepal, and Purniamarker and Katihār in India are major cities on the Koshi Plains. Kamlā, Bāghmati (Kareh) and Budhi Gandak are major tributaries of Koshi in India, besides minor tributaries like Bhutahi Balān.


Kangchenjunga south face from Nepal
In Nepal the Koshi lies to the west of Kanchenjungamarker. It has seven major tributaries: the Sun Koshi, the Tama Koshi or Tamba Koshi, the Dudh Koshi, the Indravatimarker, the Likhu River, the Arun and the Tamurmarker. The Dudh Koshi joins the Sun Koshi at the Nepalese village of Harkapurmarker. At Triveni Sun the Koshi is joined by the Arun and the Tamar, after which the river is called the Sapta Koshi. At in Nepal, it descends from the mountains and it is then called simply the Koshi. These tributaries encircle Mt Everest from all sides and are fed by the world's highest glaciers. Further down the Triveni, the river cuts a deep gorge across the lesser Himalayan range of Mahabharat Lekhmarker in a length of and debouches into the plains near Chatra. After flowing for another , it enters the north Bihar plains near Bhimnagar and after another , flows into the Ganges near Kurselamarker(1). The river travels a distance of from its source to the confluence with the Ganges.

The Kosi river fan located in the northern part of India (in northeast Biharmarker and eastern Mithila) is one of the largest alluvial cones built by any river in the world. This -long and -wide alluvial cone shows evidence of lateral channel shifting exceeding during the past 250 years through more than 12 distinct channels. The river, which used to flow near Purneamarker in the 18th century, now flows west of Saharsamarker (1). The Kosi alluvial cone and its adjoining area have been studied in detail by remote sensing techniques. The data have been integrated with the available geological and geophysical information to decipher the causes responsible for the lateral shift of such a high-magnitude fan. A satellite image shows the old palaeo-channels of the Koshi river with its former (before 1731) confluence with the Mahananda Rivermarker north of Lavamarker.

National parks and fauna

There are two famous national parks in the Koshi river basin: the Sagarmatha National Park, located in eastern Nepal, containing parts of the Himalayas and the southern half of Mount Everest and the Koshi Tappu Wildlife Reserve situated on the flood plains of the Sapta-Koshi River in Eastern Nepal.

Sagarmatha National park
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Sagarmatha National parkmarker is located in eastern Nepal, including parts of the Himalayas and the southern half of Mount Everest. The park, which is also included as a UNESCO world heritage site, was created on 19 July 1976. Sagarmatha in Sanskrit means "Forehead of Universe" (Sagar: Sky or Heavens; Matha: Forehead) and is the modern Nepali name for Mount Everest. The park covers an area of and ranges in elevation from its lowest point of at Jorsalle to at the summit of Mount Everest (highest peak in the world). Other peaks above are Lhotse, Cho-Oyu, Thamserkumarker, Nuptse, Amadablam, and Pumori. The upper watershed of the Dudh Koshi river basin system lies in the park. The types of plants and animals that are found in the park depend on the altitude.

The forests provide habitat to at least 118 species of birds, including Danphe, Blood pheasant, Red-billed chough, and yellow-billed chough. Sagarmatha National Park is also home to a number of rare species, including musk deer, wild yak, snow leopard, Himalayan black bear and red panda. Moreover, many other animals such as Himalayan thars, deer, langur monkeys, hares, mountain foxes, martens, and Himalayan wolves are found in the park.

In the lower forested zone, birch, juniper, blue pines, firs, bamboo and rhododendron grow. Above this zone, all vegetation is dwarf plants or shrubs. As the altitude increases, plant life is restricted to lichens and mosses. Plants cease to grow at about , in the permanent snowline in the Himalayas.

The park's visitor centre is located at the top of a hill in Namche Bazaar, also where a company of the Nepal Royal Army is stationed to protect the park. The park's southern entrance is a few hundred metres north of Mondzo at 2 835 m (9,300 ft), a one-day hike from Lukla.

The presence of the Sherpas, with their unique culture, adds further interest to this park. UNESCO listed the park as a World Heritage Site in 1979 for its unique natural, cultural and landscape characteristics.

Koshi Tappu Wildlife reserve

Koshi Tappu Wildlife reserve is a wetland situated in the flood plains of the Sapta-Koshi River in Nepal's Eastern Terai. Gazette-notified as a wild life reserve in 1976, it covers a reserve area of and is one of the Outstanding Important Bird Areas in the Indo-Gangetic grasslands. The park has large population of Swamp Francolin, breeding Bristled Grass-warbler, records of White-throated Bushchat and Finn's Weaver. The Koshi river forms the major landmark of the reserve and is home to 80 fish species, around 441 species of birds, 30 shore birds, 114 water birds, 20 ducks and 2 ibises. The endangered swamp partridge and Bengal florican are also found here. The Koshi Barrage is an extremely important resting-place for migratory birds (87 nos winter visitors). In view of its rich biodiversity it was declared a Ramsar site of international significance in 1987. The endangered Gharial crocodile and Gangetic dolphin locally known as sons in Bihar and a further endangered species (freshwater dolphin) have been recorded in the river.

The last surviving population of wild buffalo or arna in Nepal is found in the reserve (number at present is estimated to be 150). The reserve is a habitat of 20 other animal species such as hog deer, spotted deer, wild boar, blue bull and rock python.

The vegetation mainly includes tall khar-pater grasslands with a few patches of khair-sissoo scrub forest and deciduous mixed riverine forest.

During the monsoon, the reserve is flooded with depths ranging from .Birdwatching along the eastern embankment at dusk and dawn is one of the most exciting tourist attractions in the reserve. Gangetic River Dolphin, locally known as sons in Bihar, is an endangered species (freshwater dolphin).


The Kosi is known as the “Sorrow of Biharmarker” when it flows from Nepalmarker to Indiamarker, as it has caused widespread human suffering in the past through flooding and very frequent changes in course [224898] [224899] [224900].

The Koshi has an average water flow (discharge) of 1 564 m³/s or 55,000 cu ft/s. During floods, it increases to as much as 18 times the average. The greatest recorded flood was on 24 August 1954. The Kosi Barrage has been designed for a peak flood of (2).

Owing to extensive soil erosion and landslides in its upper catchment by factors both natural and human, the silt yield of the Kosi is about 19 m³/ha/year (10 cu yd/acre/yr), one of the highest in the world. (2). Of major tributaries, the Arun with its origins in Tibet brings the greatest amount of coarse silt in proportion to its total sediment load. The river is able to transport its heavy sediment load down the steep gradients and narrow gorges in the mountains and foothills where the gradient is at least ten meters per km. Then on the plains beyond Chatra the gradient is reduced below one meter per km, even to as little as 6 cm per km as the river approaches the Ganges. Current slows and the sediment load settles out of the water to be deposited on an immense alluvial fan that has grown to an area of about 15 000 km². This fan extends some 180 km from its apex where it leaves the foothills, across the international border into Bihar state and on to the Gangesmarker. Instead of a single well-defined channel, the river has numerous interlacing channels that shift laterally over the fan from time to time. Without sufficient channelisation, floods spread out very widely. The record flow of 24 200 m³/s is equivalent to water a meter deep and more than 24 kilometers wide, flowing down the slight slope of the alluvial fan at one meter per second.

The Kosi's alluvial fan has fertile soil and abundant groundwater in a part of the world where agricultural land is in acutely limited supply in relation to population. Subsistence farmers must balance the threat of starvation with that of floods. As a result, the flood-prone area is densely populated and subject to heavy loss of life. Floods have caused the Kosi to be called the “River of Sorrow”{3). It contributes disproportionately to India having more deaths in floods than any other country except Bangladeshmarker.Image:The Kosi, August 8, 2008.jpg|The Kosi before it flooded in August 2008Image:The Kosi, August 24, 2008.jpg|The Kosi during the August 2008 flood

2008 flood in Bihar

On 18 August 2008, the Kosi river picked up an old channel it had abandoned over 100 years ago near the border with Nepalmarker and Indiamarker. Approximately 2.7 million people were reported affected as the river broke its embankment at Kusaha in Nepalmarker, thus submerging several districts of Nepal and India. 95% of total flow of the Koshi was reported flowing through the new course. The worst affected districts included Supaulmarker, Arariamarker, Saharsamarker,Madhepuramarker, Purniamarker, Katiharmarker, parts of Khagariamarker and northern parts of Bhagalpurmarker, as well as adjoing regions of Nepalmarker. Relief work was carried out with Indian Air Force helicopters by dropping relief materials from Purnia in the worst hit districts where nearly two million persons were trapped.It has not been possible to assess the magnitude of deaths or destruction, because the affected areas are totally inaccessible. 150 persons are reported to have been washed away in a single incident (Dainik Hindustan, Darbhanga edition). Another news item stated that 42 people had died in the flood in Bihar.

The Government of Bihar has constituted a technical committee, headed by a retired engineer-in-chief of the water resource department to supervise the restoration work and closure of the breach in the East Kosi afflux embankment. Indian authorities were working to prevent further widening of the breach and channels would be dug to direct the water back to the main river bed.

The fury of the Kosi river left at least 2.5 million people marooned in eight districts of Bihar and inundated 650 km². The prime Minister of India declared it a national calamity. The Indian Army, National Disaster Response Force and non-government organizations were operating the biggest flood rescue operation in India in more than 50 years.. It is reported as the worst flood in the area in 50 years..

Glaciers, glacier lakes and GLOF

At present, in the Himalayan region, glaciers are melting and retreating resulting in formation of lakes insecurely dammed by ice or moraines. These dams are at risk of failing, causing a Glacial Lake Outburst Flood (GLOF) with flows as great as 10,000 cubic meters a second. Such floods are likely to destroy communication systems and various infrastructures like bridges roads, hydropower projects (directly or indirectly), foot trails, villages, fields and terraces, irrigation canals, and could cost hundreds or even thousands of lives. Such floods also transport huge amounts of sediment.

In the past two decades GLOF has become a topic of intense discussion within the development community in Nepal. Studies of the glaciers and glacier lakes were carried out in 1988 by a joint Sino-Nepalese team. In the Arun-Koshi river basin, there are 737 glaciers in Tibet and 229 glacier lakes, out of which 24 glacier lakes are potentially dangerous. Similarly, there are 45 glacier lakes in the Sun-Koshi basin, out of which 10 are potentially dangerous.

The Dig Tsho GLOF on 4 August 1985, completely destroyed the nearly completed Namche hydropower plant and also all the bridges, trails, cultivation fields, houses and livestock along its path to the confluence of the Dudh-Koshi and the Sun-Koshi rivers at a distance of from the Dig Tsho glacier. The Dig Tsho glacier is on the terminus of the Langmoche Glacier. This event brought into focus the seriousness of such events and the studies to assess the glaciers, glacier lakes and GLOF followed.

According to a Sino-Nepalese study, since the 1940s, there have been at least 10 cases of glacier lake outbursts within the basins investigated. Among them there have been five bursts in three glacier lakes of the Arun River Basin, and four in three glacier lakes of the Sun Koshi River Basin.

Development scenario

Multipurpose projects

After India attained independence in August, 1947, the development scenario in India has been resolute on technological development. In keeping with this approach, the National Flood Control Policy in 1954 (following the disastrous floods of 1954 in a large part of the Koshi river basin) stated that floods could be controlled through a series of flood protection works like dams, embankments and river training works. One such work which drew the immediate attention of the policy planners after independence was a solution to the recurring flood menace faced by people of North Bihar due to the Kosi and other rivers, flowing from Nepal to India. The Kosi project was thus conceptualized (based on investigations between 1946 to 1955), in three continuous interlinked stages – the first was a barrage to anchor this wayward river that had migrated about westward in the last 250 years laying waste to a huge tract in north Bihar and to provide irrigation and power benefits to Nepal and India. The second part was to build embankments both below and above the barrage so as to jacket the river within the defined channel. The third part envisaged a high multipurpose dam within Nepal at Barakshetra to provide substantial flood cushion along with large irrigation and power benefits to both countries. This was followed up by signing of the Kosi Agreement between Nepal and India on 25 April 1954 and which was revised on 19 December 1966 to address the concerns of Nepal. Further letters of Exchange to the Agreement between the two countries provided for additional schemes for providing benefits of irrigation. While the first two parts of the concept plan have been implemented at the cost of the Government of India, the third part, namely, the Koshi High dam, the kingpin of the whole concept, for various political reasons precluded any action for several years but has since been revived under a fresh agreement, in a modified form for further investigations and studies(1,2,3,4 & 5).

Details of the above projects are elaborated below.

Kosi barrage and irrigation(4&5)

Kosi Barrage, also called Bhimnagar Barrage after the name of the place where it was built between the years 1959 and 1963 straddles the Indo-Nepal border. It is an irrigation, flood control and hydropower 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 in Nepal at the Barrage site. The highest peaks – the Mount Everest and the Mount Kanchenjunga — lie in its catchment. About 10% of this catchment is snow-fed. The Eastern Canal and the Western Canal taking off from the barrage have been designed for a discharge capacity of to irrigate and to irrigate respectively. A hydropower plant has been built on the Eastern Canal, at a canal drop ( from the Koshi Barrage), to generate 20 MW. The Western Kosi Canal provides irrigation to in Nepal. A valuable bridge over the barrage opened up the East-West highway in the eastern sector of Nepal

An inundation canal taking off at Chatra, where the Kosi debouches into the plains, has been built to irrigate a gross area of 860 km² in Nepal. The project has been renovated with IDA assistance after Nepal took over the project in 1976.

Kosi embankment system (4&5)

The Kosi barrage with earth dams across river, 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 has been constructed to check the westward movement of the river. The embankments have been kept wide apart, about 12 to , to serve as a silt trap

Sapta Kosi High Multipurpose Project (Indo-Nepal)

Government of India (GOI) and His Majesty's Government of Nepal (HMGN), have agreed to conduct joint investigations and other studies for the preparation of Detailed Project Report (DPR) of Sapta Kosi High Dam Multipurpose Project and Sun Kosi Storage-cum-Diversion Scheme to meet the objectives of both the countries for Development of a) hydropower generation, b) irrigation, c) flood control/management and d) navigation.

A high concrete/Rock fill dam on the Sapta Koshi River with a dam toe underground power house with an installed capacity of 3000 MW at 50% load factor, a barrage on river Sapta Kosi about downstream of Sapta Kosi High Dam to re-regulate the water being released from the Sapta Koshi dam with two canals, Eastern Chhatra Canal and Western Chhatra Canal, off-taking from the either bank from 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 are envisaged.

A Power Canal off-taking from the Eastern Chatra Canal is proposed for conveying the water required for irrigation at existing Kosi barrage at Hanuman Nagar and also the water which may be required downstream of Hanuman Nagar Barrage for the purpose of 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 also proposed on power canal.

Necessary cushion in storage capacity of Sapta Kosi High Dam would be provided to moderate the flood downstream of dam.

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 out of which economically exploitable potential is 42,140 MW. The Koshi river basin contributes 22,350 MW of this potential.(360 MW from small schemes and 1875 MW from major schemes) and the economically exploitable potential is assessd as 10,860 MW (includes the Sapta Koshi Multipurpose Project [3300MW] mentioned above).

Adventure sports

River rafting

River rafting, also known as White Water Rafting, is an adventure sport that challenges one’s ability to row against the current of rivers. This is usually done on whitewater or different degrees of rough water, in order to thrill and excite the passengers riding on an inflatable rubber raft. It became popular as a sport during the mid 1970s and is now the third most popular adventure sport in Nepal; after mountaineering and trekking. The Sun Koshi river (The Golden River) presents the longest river trip in Nepal, traversing and meandering its way through the picturesque Mahabharata range of mountains. The river rafting trip in the Sun Koshi is listed as one of the world’s top ten classic river journeys. Other rivers where this adventure sport is a popular tourist attraction in Nepal are the Kali Gandaki, the Trisuli, the Bhote Koshi, the Marsyangdi and the Karnali. and

A classic multi-day River trip (9 days) with around 40 rapids of grade 2-5 (Rivers are graded on a scale from one to six based on rapids and difficulties in rafting through the river) is recommended for advanced Rafters and Kayakers.

Sport Fishing

The Koshi and other rivers draining the Himalayasmarker have populations of Mahseer which are esteemed as gamefish and known as Indian Salmon. Mahseer can weigh up to 50 kg. and are said to put up a greater battle than any other type of fish of equivalent weight. They will take tied streamer flies as well as bait.


External links

Reference books

3. Floods, Flood plains and Environmental Myths – State of Art of India’s Environment – A Citizens’ Report, Centre for Science and Environment, 807, Vishal Bhavavn, 95, Nehru Place, New Delhi - 110019.

4. A Framework for Sustainable Development of the Ganges- Brahmaputra- Meghna (GBM Region), Proceedings of Conference held in Dhaka, 4-5 December 1999–Nepal Water Vision in the GBM Regional Framework, Institute for Integrated Studies, Kathmandu).

4. Water Conflicts in South Asia, Managing Water Resources Disputes Within and Between Countries of the Region (2004), Published by GEE-21Honolulu Hi 96825-0517,USA.

5. Barrages in India (1981), Publication number 148, Central Board of Irrigation and Power, Malcha Marg, Chanakyapuri, New Delhi.

6. Design and Construction of selected Barrages in India (1981), Publication number 149, Central Board of Irrigation and Power, Malcha Marg, Chanakyapuri, New Delhi.

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