Mapping Coastal Erosion in Tamil Nadu Using Historical Satellite Imagery

Ramesh Saini

Independent Researcher

Himachal Pradesh, India

Abstract
Coastal erosion represents a multifaceted challenge for shoreline stability, ecological integrity, and socioeconomic resilience along the Tamil Nadu coast. This study harnesses four decades (1980–2020) of Landsat satellite imagery—spanning MSS, TM, ETM+, and OLI sensors—to map shoreline dynamics, quantify erosion and accretion rates, and pinpoint high-risk sectors. Images underwent radiometric calibration, atmospheric correction, and geometric registration before shoreline extraction via a dual approach: Normalized Difference Water Index (NDWI) thresholding complemented by supervised maximum likelihood classification. A baseline transect framework was established 500 m inland, with perpendicular transects at 100 m spacing generated in ArcGIS DSAS. We computed End Point Rate (EPR) and Linear Regression Rate (LRR) for each transect, revealing a mean retreat of 0.8 m yr⁻¹ and localized extremes up to 2.5 m yr⁻¹. Hotspots near Nagapattinam–Thiruthuraipoondi, Kanyakumari, and Ramanathapuram correlate with sediment deprivation by upstream dams, intense wave energy, and mangrove degradation. Accretion zones at river mouths underscore the role of fluvial sediment delivery. Correlation analysis implicates coastal development density (r = 0.61) and beach slope (r = 0.52) as significant drivers alongside sea-level rise (r = 0.38). Validation with 2021 differential GPS field surveys yielded a mean shoreline positional error of ±12 m, affirming methodological robustness. Findings inform coastal zone management: prioritized mitigation in erosion hotspots through nature-based solutions (mangrove restoration, dune rehabilitation), integrated sediment management, and routine satellite-based monitoring every five years. Implementing adaptive planning—restricting critical infrastructure in high-retreat zones and promoting soft engineering—will enhance resilience against climate change and anthropogenic pressures along Tamil Nadu’s dynamic coastline.

Keywords
Coastal Erosion, Shoreline Change, Tamil Nadu, Historical Satellite Imagery, NDWI, DSAS

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