IV. ANALYSIS OF SECTOR-LEVEL MEASURES USED TO INTEGRATE ENVIRONMENTAL CONSIDERATIONS IN TERMS OF PERCEIVED EFFECTIVENESS IN ACHIEVING POLICY OBJECTIVES
A. Types of measures and intended impacts: ministries and agencies responsible
3. Off-site effects of soil erosion
The loss of multipurpose reservoir capacity as a result of sedimentation is a major off-site effect. That loss has a major adverse impact on power generation and irrigation of agricultural land in the dry zone. Significant losses have been reported for some of the large reservoirs such as Polgolla (44.1 per cent in 17 years of operation) and Rantambe(27.8 per cent in four years of operation). Those figures account for an average annual loss of capacity of 2.52 per cent for Polgolla and 6.95 per cent for Rantambe. The comparatively faster capacity loss at the Rantambe reservoir may stem from the high percentage of annual crop cultivation in the area.
The other adverse effect is the rainfall run-off ratio. Changes without adequate conservation measures in land use from perennial crops, such as tea, in favour of annual crops may result in reduced reservoir capacity together with increased water yields from a rise in the rainfall run-off ratio. The net effect of such land-use changes on irrigation and hydropower generation will depend on the relative strengths of their negative and positive effects on reservoir capacity and water yield.
The increased cultivation of annual crops in contrast to perennials in hilly regions also causes damage to roads through increased erosion and rainfall run-off ratios. High erosion chokes up road drainage systems with silt, and road surfaces become flooded during high-intensity rainfall. Other adverse effects from the changeover to annual crops include frequent failures of road embankments and landslides. According to the records of the Road Development Authority, the total cost of maintaining one kilometre of A and B class roads in Nuwara Eliya District of the hill country has increased almost 350 per cent during the past five-year period.