Shoreline dynamics in response to sea-level changes on the eastern coast of Bangladesh

Abstract

The eastern coast of Bangladesh has undergone significant geomorphic changes since 1990, with the shoreline predominantly prograding towards the Bay of Bengal. Analysis indicates that the northeastern (Mirsarai- Banshkhali) coast experienced seaward progradation, with a maximum progradation of 3.87 km and an average rate of 0.13 km/year over the past 30 years. Conversely, the south-eastern coast (Cox’s Bazar toward Teknaf) exhibited landward movement due to erosion, with a maximum retreat of 2.9 km and an average rate of 0.096 km/year. These changes were quantified using remote sensing and the Digital Shoreline Analysis System (DSAS), an ArcGIS extension, to calculate Net Shoreline Movement (NSM) and Linear Regression Rate (LRR) with 95% confidence intervals. Shorelines were manually digitized from Landsat images at a fixed scale of 1:2500 to ensure precision. Mean Sea Level (MSL) data from two tidal stations revealed fluctuating trends over time. At Enayethat station, a weak uphill positive correlation was found between sea-level rise and shoreline erosion ( R 2 = 0.06), whereas at Lemshikhali station, the MSL decreased between 1990 and 2019, and a moderate uphill positive correlation ( R 2 = 0.43) with shoreline erosion was observed. The findings indicate that accretion along the eastern shoreline surpasses erosion. Sedimentation in the estuary and the stabilizing influence of eastern hills contribute to a long-term trend of shoreline stability and seaward expansion. Importantly, no direct relationship was identified between sea-level rise and coastal erosion, highlighting the dominance of localized geomorphic and sedimentary processes in shaping shoreline dynamics. These results could reflect similar patterns of change in other tropical shorelines worldwide.

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