Nepal has three categories of rivers. The largest river systems—from east to west Koshi, Gandaki/Narayani, Karnali/Goghra and Mahakali -- originate in or beyond the high Himalaya and maintain substantial flows from glacial melt through the hot, droughty spring before the summer monsoon. These largest rivers cross the mountains in deep gorges before emerging onto the plains where they have deposited megafans exceeding 10,000 km2 (3,861 sq mi) area.
the Koshi is also called Sapta Koshi for its seven Himalayan tributaries: Indrawati, Bhote Koshi, Tama Koshi, Dudh Koshi, Liku, Arun, and Tamor. The Arun rises about 150 kilometers inside Tibet.
The Gandaki/Narayani also has seven Himalayan tributaries: Daraudi, Seti Gandaki, Madi, Kali, Marsyandi, Budhi, and Trisuli also called Sapta Gandaki. The Kali Gandaki flows between the 8,000-meter (26,247 ft) Dhaulagiri and Annapurna ranges in the world's deepest valley. After the seven upper tributaries have joined, the river becomes the Narayani inside Nepal, however it is called the Gandak in India.
The Karnali drains western Nepal, with the Bheri and Seti as major tributaries. The upper Karnali rises inside Tibet near sacred Lake Manasarovar and Mount Kailash. The area around these features is the hydrographic nexus of South Asia by containing the sources of the Indus, Sutlej, Ganges tributary Karnali and Yarlung Zangbo/Brahmaputra. It is the center of the universe according to traditional cosmography. The Mahakali or Kali along the Nepal-India border on the west joins the Karnali in India, where the river is known as Goghra or Ghaghara.
Second category rivers rise in the Middle Hills and Mahabharat Range, from east to west the Mechi, Kankai and Kamala south of the Kosi; the Bagmati that drains Kathmandu Valley between the Kosi and Gandaki systems, then the West Rapti and the Babai between the Gandaki and Karnali systems. Without glacial sources, annual flow regimes are more variable although limited flow persists through the dry season.
Third category rivers rise in the outermost Siwalik foothills and are mostly seasonal.
None of these river systems support significant commercial navigation. Instead, deep gorges create obstacles to establishing transport and communication networks and de-fragmenting the economy. Foot-trails are still primary transportation routes in many hill districts.
Nepal's towns, villages, rivers and peaks
[edit] River Management
All three categories are capable of causing serious floods, for example the West Rapti in the second category is called Gorakhpur's Sorrow for its history of urban flooding. Koshi River in the first category caused a major flood in August 2008 in Bihar state, India after breaking through a poorly-maintained embankment just inside Nepal.
Since uplift and erosion are more or less in equilibrium in the Himalaya, rapid uplift is balanced by annual increments of cubic kilometers of sediments washing down from the mountains, then on the plains settling out of suspension on vast alluvial fans or inland deltas over which rivers meander and change course at least every few decades, causing some experts to question whether manmade embankments can contain the problem of flooding. Traditional Mithila culture along the lower Koshi in Nepal and Bihar celebrated the river as the giver of life for its fertile alluvial soil, yet also the taker of life through its catastrophic floods.
Another approach would be to build large dams—in gorges crossing the Mahabharat Range or further upstream—with storage capacities measured in cubic kilometers to capture high flows during the monsoon when there is usually enough rainfall on the plains if not flooding, then releasing water for hydroelectric generation and irrigation especially during the hot and dry pre-monsoon "summer". Nepal would appear to have unusual potential given its average annual 150 cm. of precipitation and thousands of meters of relief between mountains and plains, but there has only been limited development of this potential for example on the Kali Gandaki north of Tansen.
Building dams in Nepal is controversial for several reasons. First, the region is seismically active. Dam failures caused by earthquakes could cause tremendous death and destruction downstream, particularly on the densely populated Gangetic Plain. Second, global warming has led to the formation of glacial lakes dammed by unstable moraines. Sudden failures of these moraines could lead to cascading failures of manmade structures downstream. Third, sedimentation rates in the Himalaya are extremely high, leading to rapid loss of storage capacity as sediments accumulate behind dams. Fourth, there are complicated questions of cross-border equity in how India and Nepal would share costs and benefits that have proven difficult to resolve in the context of frequent acrimony between the two countries.
the Koshi is also called Sapta Koshi for its seven Himalayan tributaries: Indrawati, Bhote Koshi, Tama Koshi, Dudh Koshi, Liku, Arun, and Tamor. The Arun rises about 150 kilometers inside Tibet.
The Gandaki/Narayani also has seven Himalayan tributaries: Daraudi, Seti Gandaki, Madi, Kali, Marsyandi, Budhi, and Trisuli also called Sapta Gandaki. The Kali Gandaki flows between the 8,000-meter (26,247 ft) Dhaulagiri and Annapurna ranges in the world's deepest valley. After the seven upper tributaries have joined, the river becomes the Narayani inside Nepal, however it is called the Gandak in India.
The Karnali drains western Nepal, with the Bheri and Seti as major tributaries. The upper Karnali rises inside Tibet near sacred Lake Manasarovar and Mount Kailash. The area around these features is the hydrographic nexus of South Asia by containing the sources of the Indus, Sutlej, Ganges tributary Karnali and Yarlung Zangbo/Brahmaputra. It is the center of the universe according to traditional cosmography. The Mahakali or Kali along the Nepal-India border on the west joins the Karnali in India, where the river is known as Goghra or Ghaghara.
Second category rivers rise in the Middle Hills and Mahabharat Range, from east to west the Mechi, Kankai and Kamala south of the Kosi; the Bagmati that drains Kathmandu Valley between the Kosi and Gandaki systems, then the West Rapti and the Babai between the Gandaki and Karnali systems. Without glacial sources, annual flow regimes are more variable although limited flow persists through the dry season.
Third category rivers rise in the outermost Siwalik foothills and are mostly seasonal.
None of these river systems support significant commercial navigation. Instead, deep gorges create obstacles to establishing transport and communication networks and de-fragmenting the economy. Foot-trails are still primary transportation routes in many hill districts.
Nepal's towns, villages, rivers and peaks
[edit] River Management
All three categories are capable of causing serious floods, for example the West Rapti in the second category is called Gorakhpur's Sorrow for its history of urban flooding. Koshi River in the first category caused a major flood in August 2008 in Bihar state, India after breaking through a poorly-maintained embankment just inside Nepal.
Since uplift and erosion are more or less in equilibrium in the Himalaya, rapid uplift is balanced by annual increments of cubic kilometers of sediments washing down from the mountains, then on the plains settling out of suspension on vast alluvial fans or inland deltas over which rivers meander and change course at least every few decades, causing some experts to question whether manmade embankments can contain the problem of flooding. Traditional Mithila culture along the lower Koshi in Nepal and Bihar celebrated the river as the giver of life for its fertile alluvial soil, yet also the taker of life through its catastrophic floods.
Another approach would be to build large dams—in gorges crossing the Mahabharat Range or further upstream—with storage capacities measured in cubic kilometers to capture high flows during the monsoon when there is usually enough rainfall on the plains if not flooding, then releasing water for hydroelectric generation and irrigation especially during the hot and dry pre-monsoon "summer". Nepal would appear to have unusual potential given its average annual 150 cm. of precipitation and thousands of meters of relief between mountains and plains, but there has only been limited development of this potential for example on the Kali Gandaki north of Tansen.
Building dams in Nepal is controversial for several reasons. First, the region is seismically active. Dam failures caused by earthquakes could cause tremendous death and destruction downstream, particularly on the densely populated Gangetic Plain. Second, global warming has led to the formation of glacial lakes dammed by unstable moraines. Sudden failures of these moraines could lead to cascading failures of manmade structures downstream. Third, sedimentation rates in the Himalaya are extremely high, leading to rapid loss of storage capacity as sediments accumulate behind dams. Fourth, there are complicated questions of cross-border equity in how India and Nepal would share costs and benefits that have proven difficult to resolve in the context of frequent acrimony between the two countries.
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