Demarcation of Coastal erosion trends in Southwest coast of Sri Lanka : A case study using coastline from Kollupitiya to Kalutara North in Sri Lanka

Coastal erosion is one of the severe problems face in Sri Lanka. It has been damaging to economically valuable lands along the coastal zone. Coastal erosion occurs due to both natural processes and anthropogenic activities. The impact of coastal erosion is more severe along the Western and Southwestern coasts of Sri Lanka (CCD, 1986). The study area of this research i.e from Kollupitiya to Kalutara North within the Southwest coastal zone of Sri Lanka is one of the highly populated coastal sectors and is rich in coastal resources compared to other coastal sectors of Sri Lanka. The main objective of this study is to demarcate the areas recorded severe coastal erosion since 1956 to 2016 from Kollupitiya to Kalutara North and to identify the factors influenced for such changes. Aerial photographs of the Survey Department Sri Lanka which were produced in 1956 were used to produce digital map of the historical coastline of the area. Using the Google Earth Satellite Image (20th September, 2016), digital map of the present coastline of the study area has produced. Arc GIS software has used to overlay these two maps and to demarcate coastal erosion trends during sixty years. It was observed that coastal areas in Mount Lavinia, Moratuwa and Panadura recorded higher coastal erosion compared to other locations in the study area. According to the overlay analysis it is very clear that some of the locations in these areas were eroded more than 50 meters within sixty years. When comparing historical landuse pattern with the present status of the landuse pattern, it has been clearly identified that there is a tremendous change in urbanization in coastal areas mentioned in the above. With the increase of urbanization in and around Moratuwa, Panadura and Mount Lavinia, a significant amount of natural vegetation had removed within sixty years. Also there are several artificial structures such as hotels, industries, etc. had been established at some locations within these coastal areas. However, when analyzing the data obtained from the CCD, NAARA and Meteorological Department, natural processes and environmental conditions did not much effect on coastal erosion in the study area. Therefore, variation of coastal erosion trends from Kollupitiya to Kalutara North is mainly due to anthropogenic activities.