: The Indrawati River basin, located about 50 km North-East of Kathmandu lies in the
central region of Nepal. The river originates from the Himal region of the Mahabharat range
(5,863 m asl). From its origin, Indrawati flows southwards to meet Sunkoshi River, one of the
major rivers in Nepal at 626 m asl. The basin spans across Sub-tropical to Alpine climatic zones
and overlaps three districts, Sindhupalchok, Kavreplanchok and Kathmandu of Nepal. The
catchment area of the basin is 124,000 hectares and 40 percent of the basin is covered by forest.
The average annual rainfall at higher elevation (Sarmathang) is 3,874 mm, while it is about
1,128 mm at Dolalghat, lower elevation Zone. The average annual potential evapotranspiration
for the basin is 953.91 mm and the temperature ranges from 32.5°C to about 5°C. The average
relative humidity is about 70% and varies from 60% in the dry season to 90% in the rainy season.
The population density of the basin in 1991 was 165/km2 and the projected figure for 1998
is about 175/km2
. Ninety-six percent of the population is involved in agriculture. Farm size per
household (0.9 ha on an average) is very small. Major crops grown in the basin are rice, wheat,
maize, potato, mustard and millet. A major attraction of the basin is its National Park at the
head of the basin covering sizeable area and is one of the most favourite trekking routes of the
tourists visiting Nepal. Water in the basin is used for irrigation, for drinking by both humans
and animals, consumed by forest and vegetation, to extract hydropower and to operate water mills.
In steep terrain the variation of rainfall is high. The effects of high rainfall on soil erosion
and landslide are tremendous. At the same time, over grazing by livestock, intensive crop
cultivation and encroachment of forest and cultivation of marginal lands have caused soil
erosion and severe landslides in the basin. Majority of the soils in the basin are red soils
(Rhodustalfs) that are highly susceptible to erosion and landslides. Agricultural practices that
are adopted in the basin are also supportive to increase the rate of soil erosion.
At the same time, construction activities of development infrastructures have also
challenged the dynamic ecosystem of the basin. Recently, the Government of Nepal is
implementing Melamchi Water Supply Project (MWSP). Melamchi River basin is one of the
sub-basins of the Indrawati River basin. Kathmandu valley, the capital city of the Kingdom of
Nepal, has been suffering from the shortage of drinking water for a long time. The population
of Kathmandu valley is 1.1 million and the growth rate is about 4.82 percent per annum. The
shortage of water supply has affected public health and economic activity in Kathmandu. The
government carried out many studies to meet the water demand of Kathmandu valley. These
studies formed the basis for the implementation of the MWSP.
An environmental impact assessment (EIA) study of the Project has been carried out and
the impacts of MWSP on the environment of Indrawati River basin cannot be overlooked. The
present study is also an attempt of documentation of the effects of MWSP on soil and water in
Indrawati River basin.