Koshi River Basin (China, Nepal, India)
Koshi River (कोशी नदी in nepali or Kosi River in indian) is one of the biggest tributary of River Ganga originating from Tibet (China) and joins the Ganges in Bihar State (India) via Nepal. Total drainage area of the Koshi River is 88000 km2. Majority of the area comes from Tibet and Nepal (80%), and only 20% drainage area is in Indian Territory. The River Khosi originates at an altitude of over 7000 m above MSL in the Himalayas, 6 of the 14 eight-thousanders are in the basin (Mount Everest, Kangchenjunga, Lhotse, Makalu, Cho Oyu and Shishapangma).
In the north, the river is bound by the ridge separating it from the Tsangpo (Brahmaputra) River, while the River Ganga forms its southern boundary. The eastern and western boundaries are the ridge lines, separating it from the Mahananda and the Gandak/Burhi catchments respectively. The upper catchment of the river system lies in Nepal and Tibet. It enters the Indian Territory near Hanuman Nagar in Nepal. It joins the Ganga River near Kursela in Katihar district. In Nepal, this river is known as “Saptakoshi”. It is formed by the confluence of seven smaller streams, namely, the Sun Koshi, the Bhote Koshi, the Tama Koshi, the Dudh Koshi, the Barun Koshi, the Arun Koshi and the Tamor Koshi, meeting above Tribeni, about 10 km. upstream of Chatara. But for all practical purposes, the confluence at Tribeni in Nepal is considered to be formed by the three major tributaries out of the seven, the Arun Koshi from North, the Sun Koshi from West and the Tamor Koshi from East. Below the confluence at Tribeni, the Koshi flows in a narrow gorge for a length of about 10 km., till it debouches into plains, near Chatara in Nepal. Further down, the river runs in relatively flat plains of Nepal. The river flows through Nepal for 50 km below Chatara to Hanuman Nagar, before it enters the Indian Territory. Below Hanuman Nagar, the river Koshi runs about 100 km in a sandy tract and finds its way southward through several channels. After that, the river takes an eastward direction and has a single defined channel. The main channel joins the river Ganga near Kursela in Katihar district. In plains of Bihar, the river has two important right tributaries; these are the Bagmati and the Kamla Balan. The other tributaries worth mentioning on the right bank are the Trijuga and the Bhutahi Balan.
Socioeconomic conditions: Koshi River Basin has a population of 15.3 million (2009). The total annual GDP was about USD$ 10.4 billion in 2009 (i.e. less than USD$ 700 per capita/year). The region in India is mostly alluvial with subtropical climate and is very productive in agriculture. However, due to its large population (about 1000 people per km2), the average income in the region is below the national average of India (USD$ 1134 in 2009). The Nepalese in the region are about 6 million (1/4 of the country’s population). The population density is 200 km−2 varying from 32 (Solukhumbu) to 276 (Kavre) in the central part of the Koshi River. Forty percent of the residents are below Nepal’s poverty line (higher than the national average of 30%), but the GDP per capita in the region is near to Nepal’s national average (USD$ 427). The population in China’s territory is 94 thousand (with an average population density of 3.2 km−2 varying between 1.9 and 5.5 km−2). The average GDP per capita of Chinese in the region is USD$ 1970. Clearly, the region in the middle of the basin has the worst economic condition. The population density increases rapidly from the upstream to downstream.