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).

Development scenario

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(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 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 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 Koshi Barrage), to generate 20 MW. The Western Kosi 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
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.

2008 flood in Bihar

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 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 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 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 90 km (56 mi) 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.

Koshi Tappu Wildlife reserve

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 175 km2 (68 sq mi) 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 10 to 300 cm (3.9 to 120 in). 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).
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 24 August 1954. The Kosi Barrage has been designed for a peak flood of 27,014 m³/s (954,000 cu ft/s)(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). 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”{3). It contributes disproportionately to India having more deaths in floods than any other country except Bangladesh.