Multi-decadal shoreline variability on the eastern coast of Sri Lanka: contrasting erosion hotspots and stable control sites through quantitative assessment of coastal instability (2010-2025)

Abstract

Coastal erosion has emerged as a critical global challenge, yet large-scale quantitative assessments of shoreline variability remain scarce across tropical marine environments. Longterm, spatially resolved data are essential for distinguishing persistent geomorphic loss from seasonal fluctuations and for informing evidence-based coastal management strategies. This 15-year multi-decadal analysis (2010–2025) provides a quantitative assessment of shoreline variability across the Eastern Province of Sri Lanka, addressing data scarcity. Satellite imagery from Landsat and Sentinel-2 combined with automated shoreline detection reveals substantial spatial variation in coastal behaviour across the study area. Analysis of twelve coastal sites reveals distinct geomorphic patterns: six sites experience active erosion (Kalmunai, Oluvil North, Arugam Bay, Vakarai, Passikudah, and Foul Point) with retreat rates ranging from −0.5 to −3.5 m/yr, four sites show seaward accretion (Okanda, Kattankudy, Oluvil South, and Pulmoddai) with advance rates of +0.2 to +4.5 m/yr, and two sites maintain stable geomorphic conditions (Nilaveli and Dutch Bay). These site-specific, quantified rates enable coastal managers to prioritise intervention locations and assess the effectiveness of coastal protection strategies. The methodology demonstrates how long-term satellite-derived shoreline monitoring can fill regional data gaps and provide quantitative foundations necessary for sustainable coastal zone management and informed policy decisions in data-scarce tropical regions.