Causes and effects of siltation on the environment of Nepal

Summary

The present investigation was carried out in 1986, and is based upon about 20 years of river discharge data (1960s to 1980s). There are three important river-systems in Nepal - Sapt Kosi River system in East Nepal, Sapt Gandaki River system in mid- Nepal, and Karnali River system in West Nepal. The average annual highest rainfall is 3,685 mm yr⁻¹, and the greatest mean annual suspended sediment load (1.434 g L⁻¹) was recorded in Sapt Gandaki, while the water discharge from Sapt Kosi (1,747 m³ s⁻¹) was the highest and so also was the silt discharge (0.4 million ton day⁻¹). The correlation between water discharge and silt discharge was found to be statistically highly significant as verified by correlation and regression analyses.

An abatement of human interference in the catchment areas of these rivers, and fodder/fuelwood plantation through the active participation of local people in their marginal land to decrease the human pressure on natural forests, are considered the two major easy, effective and economic methods to control the siltation hazard that is causing extensive deterioration to the environment in Nepal.