Environmental Sustainability and Mass Movement Hazard in Kotmale Reservoir Surroundings

Abstract

Sri Lanka experienced several devastations due to mass movement in the past with the Central Highlands being the most vulnerable and mostly affected region. There was a significant increase in mass movements following the alterations to the environment and this is especially true in the sensitive environment of the Kothmale Reservoir surroundings. The introduction of Reservoir directly and indirectly made pathways to mass movements. Many other factors also interact and combine in complexity to influence such movements. The study utilized field observations and existing Maps of the area with Landsat ETN satellite images that were analyzed using MFWORKS software. 100 square kilometer surroundings of Kothmale Reservoir was the study area. Geological, Soil, Land Use, Hydrological and Slope parameters were utilized to analyze the hazard of mass movement. By comparing above parameters it was concluded that, 33% of the surroundings of the Kothmale Reservoir is highly susceptible to Mass Movements even without the Reservoir. What the reservoir has done was to contribute further to the causation of Mass Movement and thus the high hazard region had increased to 38% with 15% increase purely due to the addition of the reservoir. But it is not only the reservoir that has contributed to Mass Movements in this region. Lack of measures to regulate the dynamics of land use in this fragile environment has further worsened this critical scenario. For example, when comparing the Hazard Maps of 1992 and 2001, there was an increase in the high hazard zones. The least hazard zones which were almost 50% of the total had been reduced to 20% by the 2001 and conversely high Hazard zones had doubled their share from 20% to almost 42%. Thus stabilization of the Land Use dynamics in the Kothmale Reservoir Surroundings will be of utmost significance for the future sustainability of the Kothmale environment and to reduce the hazard of Mass Movements.