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The shoreline is a more dynamic, and complex region of all geological features present, as it has a mixed result of tidal, Aeolian, tectonic, and sometimes riverine activity. The shoreline change has its impact, but it is not so visible. To observe this a long and continuous set of data is needed. The following project is done for a shoreline length of approximately 112 km of the North of the Coromandel Coast, as a trial and error work covering the major settlements of Puducherry, Cuddalore, and Chidambaram. Data used are derived from 1972 (from SOI Toposheets) to TM data of 2013. To derive the Shoreline from the satellite data, the band ratio of Red band to the IR band is done. The shorelines are digitized and saved along with the appropriate MM/DD/YYYY added to the attribute table. Digital Shoreline Analysis System (DSAS) is an extension for ArcGIS, developed by USGS. Using the extension, transects are laid for every 50 m. Then using LINEAR REGRESSION RATE (LRR), the change for every 50 meters is analyzed.
In a long term of about 40 years, the shoreline has undergone a lot of erosion, in almost all parts of the study area, other than the coast of Vellar, and Coleroon. Understanding holistically, the northern part of the study area given in part A has undergone severe erosion which is most probably because the littoral currents have null or very minimal effect on the coast of Puducherry and Cuddalore, due to the artificial coasts and seawall constructions. The effect of the artificial coast is so evident that the North and South coast has severely eroded, and stands in contrast.
Whereas the short-term variations there has been a general trend of erosion from the base year of observation, 1972 (SOI Toposheet) to 1980 (LANDSAT MSS) which accounts for around 12.65 Km2. But then, there is a change of trend from 1980-1999 where the coast shows a depositional environment, for about 4.9 Km2, and erosion for 2.15 Km2, which, comparatively a strong change in the trend of the coast. This, again continues for further for the time between 1999-2002, Where the accretion has dominated, creating deposits for 7.53 Km2, and erosion in the region is a mere 0.408Km2, and major erosion is seen in the north side of the mouth of Coleroon (0.181 Km2). This accretion might have been due to the sediment dump in the Bay of Bengal, from the rivers, which got redistributed along the coast.
But again, in-between the period of 2002-2006 the whole shore has undergone erosion of about 6.03 Km2, which is most probably due to the Tsunami in the Indian Ocean, on December 24, 2004. Due to the lack of data availability, this is still a probable conclusion only. Accretion is seen in the shore of Puducherry, owing to the construction of a harbor, which became fully functional in the year 2003. From 2006 to 2009, the area of accretion is only 0.1 Km2, but the area eroded is 4.65 Km2.
Co-Author - Salghuna N N