Author:

Abstract

A number of multipurpose reservoirs have been impounded in the Upper Mahaweli Catchment (UMC) mainly to generate hydropower, which contributes to about 40-50% of the total hydropower production in the country. The natural forest cover of the UMC has been gradually decreased during the last two centuries due to the large-scale deforestation for plantation agriculture. Subsequently, the forest cover in the hill country has been reduced further to a few isolated patches in order to meet the demand for agriculture, developmental activities and human settlements. Today, vegetables are grown extensively on the steep slopes of the UMC without proper land management practices. Consequently, this agriculturally active land is exposed to severe soil erosion and landslides, in parallel with the rapid rate of deforestation.

Estimates of the rate of soil loss on hill slopes and sediment yields in the fluvial system of the UMC indicate that the human-mediated activities in the UMC have increased rates of ongoing erosion by > 100 times over the background rates of natural erosion. Thus, the river Mahaweli and its tributaries carry enormous amounts of sediments during the rainy seasons, both as bed and suspension loads downstream and large amounts are deposited in the multipurpose reservoirs leading to a reduction of their storage capacities. Siltation in hydropower reservoirs could pose a serious threat, leading to the reduction of hydropower generation in the country and a worsening situation could be anticipated in the future. Therefore, proper management of the land by minimizing the in-situ erosion and preserving the detached soil within the catchments through effective conservation measures need to be implemented in order to ensure a steady and continuous power supply from the hydropower resources.

Keywords: Cosmogenic nuclides, erosion, hydropower generation, landslides, land use, siltation.

doi :10.4038/jnsfsr.v38i1.1721

J.Natn.Sci.Foundation Sri Lanka 2010 38 (1): 3-14

Keywords: Cosmogenic nuclides, erosion, hydropower generation, landslides, land use, siltation