Mapping and Analysis of Land Use/ Land Cover Change in Kelani Watershed, Sri Lanka

The Kelani watershed is recognized as the second largest watershed in Sri Lanka. Kelani river is the main drinking water resource of people those who live in the Kelani catchment area. Kelani watershed is a productive eco-system which provides habitats for various inherent plant and animal species. But at present, it has been revealed that various human activities affect badly on the watershed of the Kelani river. Land Use/ Land Cover (LULC) change in the watershed can directly or indirectly impact on the natural balance of the terrestrial and aquatic eco-systems of the watershed area. In the present study, an attempt was made to detect the LULC change in the Kelani watershed during past nineteen years from year 2000 to 2019. Kelani watershed region which was the study area of the present research was delineated using SRTM (Shuttle Radar Topography Mission) DEMs (Digital Elevation Models). Satellite images of years 2000, 2010 and 2019 were classified according to the LULC types using Supervised Classification technique. The classified images were subjected to the analysis in order to determine the extent of each LULC type and their changes. In the present study, the quantities of LULC changes which have taken place in the Kelani watershed from year 2000 to 2019 were determined and mapped. Post classification change detection analysis was executed using cross classification technique on a pixel by pixel basis. It resulted in a two-way cross matrix containing different combinations of "from-to" change classes and a thematic layer representing them. The vegetation cover in year 2000 has been decreased by 333 km2 during the 19 years’ time period. Built-up areas have been increased by 367 km2. Bare lands have been decreased by about 21 km2. Water bodies have been decreased by 13 km2. This study illustrated that the extent of the water bodies, bare land and vegetation which were present in year 2000 have been declined by around 41%, 17% and 17% respectively within the nineteen years’ time period. Increment of built up areas was 208% during the same time period. Obtained results provided better evidences of deforestation and rapid urbanization in the study area