Shoreline change rate estimation: Impact on salt production in Kutubdia Island using multi-temporal satellite data and geo-statistics

Abstract

The coastline is a natural interface that separates the wet and dry parts of the beach. Shoreline configuration is always influenced by natural and anthropogenic forces. Storm surge is one of the major natural events that has converted the shape of shoreline along the Kutubdia island. With the use of the Digital Shoreline Analysis System (DSAS), the coastal area was evaluated to estimate the change dynamics of Kutubdia Island. This highly active coast with erosion and deposition has inherent complexity in determining the shoreline movement and quantifying the rate of change. The study examined the positional change of the shoreline of the island between 1980 and 2021 including its impacts on salt production using Geographic Information System (GIS) tools and multi-temporal LANDSAT images. To distinguish between water and land features, the LANDSAT images were radiometrically corrected and a spectral index, the Normalized Difference Water Index (NDWI) was used. The shorelines were extracted using a histogram-based Otsu's Binary threshold approach and image-based visual interpretation. The Shoreline Change Envelope (SCE), Linear Regression Rate (LRR), and End Point Rate (EPR) was used to calculate shoreline change rates. EPR and LRR both estimated average change rates of −4.125 m/yr and −4.647 m/yr, respectively. Between 1980 and 2021, an overall land area of 9.2439 sq. km was lost, while there were no significant land depositions. The landward movement was more noticeable on the northern side of the island. The eastern side showed no significant alterations. The short-term (in 2031) and long-term (in 2041) coastline positions have been forecast based on the demarcated shoreline. The results of the forecast also show that the shoreline will move landward but not significantly seaward. Island erosion is particularly dangerous in the northern and southern zones. The result also shows that salt production is decreasing due to island erosion, especially in the south. If the erosion continues at the same rate salt production will decrease almost by 4563.38 tons between 2021 and 2041. The results of this study may help with the proper management and planning for Kutubdia Island. Moreover, this can also be used in statistical modeling, to predict where the shoreline will be in the future.