History of Koshi River
The Kosi River, called Koshi in Nepal (कोशी नदी), is a transboundary river between Nepal and India, and is one of the largest tributaries of the Ganges. The river, along with its tributaries, drains a total area of 69,300 km2 (26,800 sq mi) up to its confluence with the Ganges in India (29,400 km2/11,400 sq mi in China, 30,700 km2/11,900 sq mi in Nepal and 9,200 km2/3,600 sq mi in India). The watershed also includes part of Tibet, such as the Mount Everest region, and the eastern third of Nepal. The river basin is surrounded by the ridges separating it from the Brahmaputra in the north, the Gandaki in the west, the Mahananda in the east, and by the Ganges in the south. The river is joined by major tributaries, approximately 48 km (30 mi) north of the Indo-Nepal border, 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 120 kilometres (75 mi) 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 Bangladesh 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 Bihar, the most flood-prone area of India.
Formerly Kauśiki (named after sage Viśvāmitra because Viśvāmitra is said to have attained the status of Vedic ṛṣi or Rishi on its banks; Viśvāmitra was descendant of sage Kuśika and was called Kauśika in Rgveda), in Nepal and Bihar in northern India is a major tributary of the Ganges (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.
From Katmandu, there is a road for some distance followed by trekking paths to Mt Everest, which crosses four major tributaries of the Koshi. Namche Bazar 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 Purnia 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.
In Nepal the Koshi lies to the west of Kanchenjunga. It has seven major tributaries: the Sun Koshi, the Tama Koshi or Tamba Koshi, the Dudh Koshi, the Indravati, the Likhu, the Arun and the Tamur. The Dudh Koshi joins the Sun Koshi at the Nepalese village of Harkapur. At Triveni Sun the Koshi is joined by the Arun and the Tamar, after which the river is called the Sapta Koshi. At Barāhkṣetra 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 Lekh in a length of 10 km (6.2 mi) and debouches into the plains near Chatra. After flowing for another 58 km (36 mi), it enters the north Bihar plains near Bhimnagar and after another 260 km (160 mi), flows into the Ganges near Kursela). The river travels a distance of 729 km (453 mi) from its source to the confluence with the Ganges.
The Kosi river fan located in the northern part of India (in northeast Bihar and eastern Mithila) is one of the largest alluvial cones built by any river in the world. This 180 km (110 mi)-long and 150 km (93 mi)-wide alluvial cone shows evidence of lateral channel shifting exceeding 120 km (75 mi) during the past 250 years through more than 12 distinct channels. The river, which used to flow near Purnea in the 18th century, now flows west of Saharsa. 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 River north of Lava.
Floods
The Kosi is known as the “Sorrow of Bihar” when it flows from Nepal to India, as it has caused widespread human suffering in the past through flooding and very frequent changes in course.
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 24,200 m³/s (850,000 cu ft/s) on August 24, 1954. The Kosi Barrage has been designed for a peak flood of 27,014 m³/s (954,000 cu ft/s).
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. 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, but on the plains beyond Chatra where slopes are flatter the sediment load is deposited in 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 Ganges. 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”. It contributes disproportionately to India having more deaths in floods than any other country except Bangladesh.
2008 flood in Bihar
On August 18, 2008, the Kosi river picked up an old channel it had abandoned over 100 years ago near the border with Nepal and India. Approximately 2.7 million people were reported affected as the river broke its embankment at Kusaha in Nepal, 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 Supaul, Araria, Saharsa,Madhepura, Purnia, Katihar, parts of Khagaria and northern parts of Bhagalpur, as well as adjoing regions of Nepal. Relief work was carried out with Indian Air Force elicopters 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 65,000 hectares. The prime Minister of India declared it a national calamity. The Indian army 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.
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 120 km (75 mi) 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.
Details of the above projects are elaborated below.
Kosi barrage and irrigation. 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 61,788 km2 (23,856 sq mi) 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 455 cubic metres per second (16,100 cu ft/s) to irrigate 612,500 hectares (1,514,000 acres) and 210 cubic metres per second (7,400 cu ft/s) to irrigate 356,610 hectares (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 Koshi Barrage), to generate 20 MW. The Western Kosi Canal provides irrigation to 25,000 hectares (62,000 acres) 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 86 000 ha 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 246 km (153 mi) has been constructed to check the westward movement of the river. The embankments have been kept wide apart, about 12 to 16 km (9.9 mi), 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 269-metre (880 ft) 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 8 km (5.0 mi) 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.
Hydropower
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.
Formerly Kauśiki (named after sage Viśvāmitra because Viśvāmitra is said to have attained the status of Vedic ṛṣi or Rishi on its banks; Viśvāmitra was descendant of sage Kuśika and was called Kauśika in Rgveda), in Nepal and Bihar in northern India is a major tributary of the Ganges (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.
From Katmandu, there is a road for some distance followed by trekking paths to Mt Everest, which crosses four major tributaries of the Koshi. Namche Bazar 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 Purnia 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.
In Nepal the Koshi lies to the west of Kanchenjunga. It has seven major tributaries: the Sun Koshi, the Tama Koshi or Tamba Koshi, the Dudh Koshi, the Indravati, the Likhu, the Arun and the Tamur. The Dudh Koshi joins the Sun Koshi at the Nepalese village of Harkapur. At Triveni Sun the Koshi is joined by the Arun and the Tamar, after which the river is called the Sapta Koshi. At Barāhkṣetra 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 Lekh in a length of 10 km (6.2 mi) and debouches into the plains near Chatra. After flowing for another 58 km (36 mi), it enters the north Bihar plains near Bhimnagar and after another 260 km (160 mi), flows into the Ganges near Kursela). The river travels a distance of 729 km (453 mi) from its source to the confluence with the Ganges.
The Kosi river fan located in the northern part of India (in northeast Bihar and eastern Mithila) is one of the largest alluvial cones built by any river in the world. This 180 km (110 mi)-long and 150 km (93 mi)-wide alluvial cone shows evidence of lateral channel shifting exceeding 120 km (75 mi) during the past 250 years through more than 12 distinct channels. The river, which used to flow near Purnea in the 18th century, now flows west of Saharsa. 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 River north of Lava.
Floods
The Kosi is known as the “Sorrow of Bihar” when it flows from Nepal to India, as it has caused widespread human suffering in the past through flooding and very frequent changes in course.
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 24,200 m³/s (850,000 cu ft/s) on August 24, 1954. The Kosi Barrage has been designed for a peak flood of 27,014 m³/s (954,000 cu ft/s).
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. 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, but on the plains beyond Chatra where slopes are flatter the sediment load is deposited in 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 Ganges. 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”. It contributes disproportionately to India having more deaths in floods than any other country except Bangladesh.
2008 flood in Bihar
On August 18, 2008, the Kosi river picked up an old channel it had abandoned over 100 years ago near the border with Nepal and India. Approximately 2.7 million people were reported affected as the river broke its embankment at Kusaha in Nepal, 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 Supaul, Araria, Saharsa,Madhepura, Purnia, Katihar, parts of Khagaria and northern parts of Bhagalpur, as well as adjoing regions of Nepal. Relief work was carried out with Indian Air Force elicopters 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 65,000 hectares. The prime Minister of India declared it a national calamity. The Indian army 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.
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 120 km (75 mi) 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.
Details of the above projects are elaborated below.
Kosi barrage and irrigation. 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 61,788 km2 (23,856 sq mi) 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 455 cubic metres per second (16,100 cu ft/s) to irrigate 612,500 hectares (1,514,000 acres) and 210 cubic metres per second (7,400 cu ft/s) to irrigate 356,610 hectares (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 Koshi Barrage), to generate 20 MW. The Western Kosi Canal provides irrigation to 25,000 hectares (62,000 acres) 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 86 000 ha 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 246 km (153 mi) has been constructed to check the westward movement of the river. The embankments have been kept wide apart, about 12 to 16 km (9.9 mi), 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 269-metre (880 ft) 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 8 km (5.0 mi) 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.
Hydropower
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.
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