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Total annual internal renewable surface water resources are an estimated 78 km3 (Table 3). Because of the mountainous character of the country, groundwater resources are probably limited and are drained by the surface water network, which means they are more or less equal to overlap between surface water and groundwater. Surface water leaving the country to India is an estimated 78 km3.
Nearly every valley in Bhutan has a swiftly flowing river or stream, fed either by the perennial snow, the summer monsoon or both. Except for a small river in the extreme north, which flows north, all rivers flow south towards India. The river basins are oriented north-south and are, from west to east, the Jaldhaka, Amo (Torsa), Wang (Raidak), Mo, Puna Tsang (Sankosh), Mao Khola/Aie, Manas (Lhobrak) and eastern river basins, this last basin is composed of the Bada and Dhansiri rivers.
Most rivers are deeply incised into the landscape and hence the possibilities for run-of-the-river irrigation are limited.
There are only two wastewater collection and treatment projects in the cities of Thimphu and Phuntsholing.
There are numerous natural lakes, many are located above 3 300 m and some above 4 200 m, which are primarily used to raise fish.
Several large dams have been constructed to generate hydroelectric power. These include the 40 m high Chhuka dam (CHPP) on the Wang river in Chhukha district in the southwest, the 91 m high Tala-Wankha dam further downstream on the Raidak river near Phuntsholing town, the 33 m high Kurichhu dam on the Kuri river in Mongar district in the east, the Basochu dam (BHPP) near Wangduephodrang town in the centre-west. The 141 m high Punatsangchu dam on Puna Tsang river downstream of Wangduephodrang town is under construction.
Total hydropower generation capacity was 477 MW in 2006, of which 336 MW from the Chhukha hydropower plant, 60 MW from the Kurichu hydropower plant and 24 MW from the Bashocu hydropower plant. Hydropower represented 96 percent of the country’s electricity generating capacity and 99.9 percent of its electricity generation in 2006. With the commissioning of the first two units of the Chhukha hydroprojects in 1986, and the other two units in 1998, the electricity generation capacity substantially increased and Bhutan became a significant exporter of electricity to India. With the commissioning of the Tala Hydro Power Project in 2007, there has been a substantial improvement in the country’s energy generation.
The expansion of hydropower production capacity has had an enormous impact as, by the end of the Ninth Five-year Plan (2002-2007), the energy sector contributed to around one-quarter of GDP. With a further doubling of capacity envisaged by the end of the Eleventh Five-year Plan (2014-2019), the energy sector will probably contribute close to half of GDP.
The following hydroelectric projects have been identified for future development:
- Mangdue Chu Hydroelectric Project, with the cooperation of Norway, was planned in the Ninth Five-year Plan (2002-2007) and it is expected to be completed in the Tenth Five-year Plan (2008–2013). The project comprises two dams.
- Sunkosh Multipurpose Project (SMP) is the largest proposed hydroelectricity project in Bhutan.