Long-term erosion at the north of Hatiya Island in the Lower Meghna Estuary, Bangladesh

Hatiya Island, located in the Lower Meghna River Estuary, facing the Bay of Bengal, has experienced significant shoreline erosion at its northern tip over the past several decades. We analyzed satellite imagery from 1973 to 2021, alongside cross-sectional survey data of the Hatiya Channel, to quantify erosion rates and assess changes in estuarine channel configurations. Our findings indicate that the northern shoreline of Hatiya Island has retreated by approximately 12 km, with erosion rates ranging from 100 m/year to 550 m/year. According to the survey results, thalweg migration in the Hatiya Channel guided the shore position of the northern part of Hatiya Island in the middle two decades (1983–2000), with shoreline shifting and thalweg migration rates of 309 m/year and 384 m/year, respectively. From 2000 to 2020, the emergence and advancement of a submerged sandbar influenced thalweg migration, resulting in shoreline and thalweg migration rates of 166 m/year and 171 m/year, respectively. Analysis of river discharge, tidal water levels, and wave data suggests that variations in river discharge significantly impact the Hatiya Channel's configuration, altering shoreline positions. Thalweg migration and the progression of the submerged sandbar are likely the primary drivers of shoreline changes on northern Hatiya Island.