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.