Koshi river system is trans-boundary river originating from Tibetan Plateau, crosses the Himalayas and flows through Mahabharat range and Siwalik hills, reaching the plains of eastern Nepal and finally meeting Ganges in India. It is the largest river basin of Nepal. Indrawati, Sun Koshi, Tama Koshi, Likhu, Dudh Koshi, Arun and Tamor are the major seven tributaries of Koshi river system. Koshi river system drains about 45% area out of 87,970 sq. Km in Nepal (Shrestha et al. 2016). Along with these river tributaries, Koshi basin comprises about 845 glaciers and 599 glacial lakes towards the North (CBS 2019). The average flow of Koshi river at confluence is around 1500 m3/s (recorded at Chatara station). These seven tributaries meet at Triveni, from where it is called Sapta-Koshi. Precipitation in this basin is influenced by summer monsoon, with 80% annual precipitation. The basin receives high precipitation and is prone to glacial lake outburst flood (GLOF), soil erosion, landslides, flood, debris flow and inundation hazards. Baidyanath Khola watershed in Kamala sub-basin and Tamor Watershed in Koshi river basin are highly exposed watersheds within the basin towards climate change risk. Watersheds of Koshi basin are 2nd among overall vulnerability index to climate change (Siddiqui et al. 2012). Within the basin, there are 34 discharge gauging stations (Jha 2011).
The basin offers high potential for hydro-power development in high hills and irrigation in plains. The power power estimates of Koshi basin is about 17008.3 MW (Jha 2011). Till date, 11 hydro-power projects have been proposed throughout the basin. The Arun III, Bhote Koshi, Lower Arun, Sundarijal, Sun Koshi 3, Tama Koshi, and Upper Arun are ROR schemes, while the Dudh Koshi, Sapt Koshi, Sun Koshi, and Tamor are storage dams. Highest mountain peaks, protected areas and ecologically rich areas provides best place for other tourism activities. Besides these, water based eco-tourism activities like white-water rafting, canyoning, fishing, etc can flourish throughout the basin. Koshi basin supports about 15% of the Nepal’s population (CBS 2014).
In 1954, Nepal and India agreed on an agreement for the construction of Koshi barrage at Nepalese territory near Indo-Nepal boarder, a multi-purpose design aimed at providing hydroelectric power, irrigation and flood control, mainly for India (Subedi 1999).
Subedi, S. P. (1999). Hydro-diplomacy in South Asia: The conclusion of the Mahakali and Ganges river treaties. The American Journal of International Law, 93(4), 953-962.
Jha, R. (2011). Total run-of-river type hydro-power potential of Nepal. Hydro Nepal: Journal of Water, Energy and Environment, 7, 8-13. https://doi.org/10.3126/hn.v7i0.4226
Siddiqui, S., Bharati, L., Panta, M., Gurung, P., Rakhal, B., & Magarjan, L. D. (2012). Climate change and vulnerability mapping in Watersheds in Middle and High Mountains of Nepal. Department of Soil Conservation and Watershed Management (DSCWM), Government of Nepal.
CBS (2014). National Planning Commission Secretariat, Central Bureau of Statistics. Government of Nepal, Kathmandu, Nepal.
Shrestha, A. B., Bajracharya, S. R., Sharma, A. R., Duo, C., & Kulkurni, A. (2016). Obesrved trends and changes in daily temperature and precipitation extremes over the Koshi river basin 1975-2010.
CBS. (2019). Environment statistics of Nepal. National Planning Commission, Government of Nepal