Comprehensive analysis of shoreline fluctuation pattern in and around Gangasagar Coast, Sundarbans Delta, India

The Gangasagar coast, forming the southern fringe of the Sundarbans delta, represents one of the most dynamic and hazard-prone coastal environments of eastern India. Over the past five decades (1975 to 2025), the shoreline has undergone significant spatial and temporal shifts, documented through satellite imagery, topographic analysis, and systematic field observations. Historical shoreline positions were extracted from Landsat datasets using MNDWI analysis at 8-15 year intervals, allowing spatio-temporal comparisons that reflect post-cyclone shoreline adjustments. Variations in the low water line across Beguakhali, Gangasagar and Dhublat sectors reveal alternating episodes of erosion and accretion controlled mainly by recurrent cyclonic disturbances. Intense storms such as Aila, Amphan, and Yaas triggered large-scale coastal retreat, embankment collapse, and mangrove degradation. Phases of limited recovery were observed only during relatively calm intervals, yet subsequent events repeatedly reversed these trends. Between 1975 and 2025, the shoreline retreated landward by approximately 697 m at Beguakhali, 69 m at Gangasagar, and 1064 m at Dhublat, indicating the highest erosion intensity in the Dhublat sector. The cumulative geomorphic imprint of recurring cyclones indicates a long-term transformation of the Gangasagar shoreline towardincreasing instability, reduced sediment resilience, and progressive loss of coastal land and ecosystem integrity.