Detecting changes of shoreline at Kuakata coast using RS-GIS techniques and participatory approach

Abstract

The land-water interface is of great importance due to its significance in resource extraction, coastal management and climate change vulnerability analysis. In the recent years, determination of shoreline requires more concern as the coast of Bangladesh is vulnerable to anticipated sea level rise due to climate change. Region specific shoreline determination is needed for resource extraction, coastal risk management and landuse planning. This report is produced to address the areas of erosion, accretion and stable shoreline along the coast of Kuakata for providing a basis to describe the extent of economic and environmental effects of present shore erosion and accretion. In this study, the shoreline change is primarily detected for three decades by comparing satellite imagery of 1989, 2003 and 2010, using Landsat TM 30m resolution images. Band Combination, Ratio Transformation, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) algorithms are used to extract shoreline from land water boundary. Later Band Combination (BC) is specifically used to measure the differences from year to year. These change detections were compared and verified by using Participatory Rural Appraisal (PRA) tools like- Transect Walk, Time Line Analysis, Cause and Effect Diagram, Key Informant Interview and Focus Group Discussion. Application of these tools also reveals the impacts due to this change. The study area, Kuakata, is a dynamic coast. Comparison of distances between derived shorelines and reference shorelines consistently shows that from 1989 to 2010 total 11.81 km2 coastal land has been eroded and 2.34 km2 land has been accreted. The coastline is retreating about 4.7 km2 per decade. Information from the Participatory Rural Appraisal (PRA) implies that, at the coast of Kuakata, the rate of erosion is higher than the rate of accretion. This result validates the finding of image interpretation from RS-GIS method. It shows that mainly fisheries and tourism is affected by the shoreline change. Marine and climatic factors are the main causes of this change. This complex shoreline change has great significance since it is one of the major tourist spots in Bangladesh.