456-MW Upper Tamakoshi hydropower project under construction (photo courtesy Bimal Gurung)
By Prakash Kaini and George Annandale
Nepal has huge potential for hydropower development. The rough estimate of the potential is more than 80,000 MW. However, the installed hydro capacity as of 2018 is less than 1,000 MW.
Nepal Electricity Authority (NEA), a government entity, owns and operates the national grid. About 60% of the 30 million people living in the country have access to electricity. The rest of the population still relies on primitive methods of lighting, such as kerosene lamps. The supply of electricity, however, relies heavily on imports from India, mainly during the winter when the river flows become very low.
The expectation has always been that energy security and the economic prosperity of the country will depend highly on hydropower development. In part, the reason for this expectation is the lack of other conventional energy resources in Nepal. Recently, Nepal signed a power trade agreement (PTA) with India that has enabled the exchange of power across the border. In addition, Nepal signed a power development agreement (PDA) for the 900-MW Arun III and 900-MW Upper Karnali hydro projects with the developers from India. These projects will export power to India, with Nepal benefitting from the royalties and taking possession of the projects in about 25 to 30 years. The direct benefit of these two big projects to the current power shortage in Nepal is minimal, but the hope is that this type of development will attract more foreign investment to the country.
Nepal’s huge hydropower potential is due to many perennial rivers, which start from the high Himalayan Mountains rising above 8,000 m in the north, flowing through the mountains toward low-lying plains in the south, and continuing on to India. The sources of water for these rivers are snow melt, glaciers and rainfall. On average, Nepal receives 1,500 mm of annual rainfall. The topography, with its high relief and high river flow, provides potential for abundant hydropower development.
Figure 1 shows the major river systems with the topographic variation within Nepal. The watershed boundary of most of these Rivers is the Himalayan border between Nepal and China, except for the Arun River, which extends into Tibet.
Figure 1: Topography and Four Major Rivers of Nepal
The four major river systems, from east to west respectively, are Koshi, Gandaki, Karnali and Mahakali. In addition, there are several smaller rivers, which originate from the mid-hills. The basin-wide hydropower potential of the country is as follows:
- Karnali and Mahakali river basins have a catchment area of 48,811 km2 and 16,097 km2, with approximate hydropower potential of 36,180 MW (the watershed area of the Mahakali River lies in India and Nepal)
- Gandaki river basin has a catchment area of 36,607 km2 and approximate hydro potential of 20,650 MW
- Koshi river basin has a catchment area of 57,700 km2 and hydro potential of 22,350 MW (the watershed area lies in Tibet/China and Nepal)
- Other river basins (i.e., southern rivers) have a catchment area of 3,070 km2 and hydro potential of 4,110 MW
Of the rough estimate of Nepal’s hydropower potential of more than 80, 000 MW, half is considered economically feasible. However, recent updates of the overall potential are lacking.
Figure 2 shows the major hydropower projects in different stages of development.
Figure 2: Major Hydropower Projects in Nepal
The annual consumption of electricity in Nepal is about 100 kWh per person, which is very low compared to the electricity use in other countries, such as more than 12,000 kWh per person in the U.S. and 500 kWh and 3,900 kWh per person in India and China, respectively. The energy use indirectly indicates the country’s level of development. Nepal imports 700 MW firm power to balance the shortage of power, especially in the winter.
To reach the level of electricity use in different countries, Nepal would need installed capacity of 4,000 MW to equal India, 31,000 MW to equal China and 96,000 MW to equal the U.S.
The way forward
Nepal needs rapid hydropower development to meet its power demand, which is growing 10% every year. However, this growth can be higher once the power is readily available at an affordable price. The bulk of the demand at present is for lighting. In the future, the industrial and domestic electricity demand will grow.
Some of the major issues of hydropower development are itemized below:
1. There is a lack of proper planning for hydropower development. It is highly recommended to make a hydropower master plan covering all four major river basins and to prioritize projects based on different factors, including technical, economic, proximity to the load center, etc. Projects need to be planned based on the rational demand forecast inside the country. By constructing cascade projects, there can be a huge saving in the headworks and in access roads and power evacuation.
2. Hydropower sites are not unlimited and, even more important, good sites are very limited. For example, Upper Tamakoshi is an ideal hydropower site due to the 300 m of head available just at one spot due to a massive landslide and deposition, which occurred a few thousand years ago. Upper Karnali is another ideal site because of the river bend, which provides 150 m of head without a dam in a stretch of 2 km. The Arun River is such a good river for hydropower because the base flow of the river is very high as most of the watershed lies in Tibet. The average rainfall in the watershed is low but the large catchment area and high altitude makes up for it, resulting in high base flow and low seasonal flow variation compared to all other rivers in Nepal. Therefore, the country should not only identify potential projects but select the best projects to meet its immediate and medium-term needs. Only when this has been accomplished should the country lease projects for export that are deemed necessary in the system in 25 to 30 years’ time horizon. Nepal needs more reservoir projects for reliable power supply throughout the year. Reservoirs store water when there are high flows during the monsoon season, which will be used to generate power when the river flow is low in the winter.
3. The government should create a favorable environment by investing in such infrastructure as roads and transmission lines. Roads are not only for hydropower. This will make the hydro projects, including reservoir projects, more attractive to develop.
4. Upper Tamakoshi can be a model project. It is a large daily peaking project (456 MW) that is financed internally, and it generates relatively cheaper energy to the consumers as well. This is proof that such an investment can be accomplished internally. If the government invests in infrastructure, many hydropower sites can be very attractive.
5. The country should invest in data collection and quality control. The large investment depends on the hydrologic data, which is not adequate.
6. The system has over 30% loss in the transmission and distribution system. This should be reduced to at least 15%. Improvement in substations and the transmission and distribution lines, as well as controlling theft of power needs to be in effect.
7. Sediment study is usually overlooked. It needs to be properly addressed in any hydropower project to keep the reservoir capacity maintained for the long run and to keep the wear and tear low on the turbine and other hydraulic machinery. Sediment management is a challenge where the rivers carry a huge amount of sediment during the monsoon season, which needs to be considered seriously.
Prakash Kaini, PhD, PE, is a hydropower/water resources engineer and George Annandale, PhD, PE, is a water resources/sediment expert.