Modeling Spatio-Temporal Shoreline Shifting of a Coastal Island in Bangladesh Using Geospatial Techniques and DSAS Extension

Abstract The study attempted to assess the changes in shoreline and erosion-accretion of newly formed island at the mouth of the Meghna river estuary in Bangladesh using multi temporal satellite images and GIS techniques. The current study used NDWI an MNDWI to delineate land and water boundary to extract the shoreline and also used some overlay analysis to measure the erosion-accretion. DSAS extension is used for analyzing the shifting of the shoreline. The results (1990-2015) show that the island has 1192 hectares of land accreted during this time period, and about 1 km of its shoreline lost during this time period as it has broken in few places. Most accretion found in the northwestern part and erosion in southeastern and southwestern part. The study area was divided into four different segments and about 115 transects were constructed, of which about 74 shows the seaward movement and 44 shows landward movement. Seaward movement and rate of shoreline shifting is higher in the northwestern part where net shoreline movement (NSM) is +1897 meters and end point rate (EPR) is +73 m/year. Landward movement and the rate of shoreline shifting are higher in southeastern and southwestern part of which net shoreline movement (NSM) is about -2680 meters and end point rate (EPR) is about -129 m/year. The highest landward movement is found as -2680 meters and highest seaward movement as +1897 meters. Accretion process is dominant while erosion process discontinued the shoreline in some places.