AEGAEUM JOURNAL ISSN NO: 0776-3808
Cyclone and its Effect on Shoreline Changes in Archaeological Sites, East Coast of Tamil Nadu, India
Sathiyamoorthy G, *Sivaprakasam Vasudevan, Selvaganapathi R & Nishikanth C. V
Department of Earth Sciences, Annamalai University, Annamalainagar, Tamil Nadu, India.
ABSTRACT : The contact line between sea and land, is knows as shoreline and they are experiencing changes due to the long-shore current, tides, wave, and storm surges, etc. The Shorelines played a major role in human settlement and favours the clustering of Port cities from ancient to present. The changes in the shoreline directly affect the livelihood of the coastal cities and also worn out the maritime archaeological sites, particularly during the late Quaternary period. A few archaeological sites including Arikamedu, Poompuhar, Tharangambadi, and Sembiyankandiyur show a direct/indirect relationship with the shoreline changes between 1972 and 2018. The shoreline changes between Pondicherry and Nagapattinam patch, with respect to the archaeological sites, quantify erosion -20.52 m/period in Arikamedu, Poompuhar, and Tharangambadi and -25.28 m/period along Sembiyankandiyur region during a span of 46 years. The maritime Archaeological, pride sites like Poompuhar, Tharangambadi and Sembiyankandiyur on the coastal region were submerged in the sea, the remand parts are also under the threat to vanish at a faster rate.
Keywords: LRR, EPR and NSM, Erosion and Accretion.
1. INTRODUCTION Coastal region of the south eastern part of India is significant with respect to archaeological studies. The modest tide and wave action in the Bay of Bengal has enabled the formation and continuance of many coastal sites. The regions like Arikamedu, Poompuhar, Tharangambadi and Sembiyankandiyur in Tamil Nadu are well suited for the study of maritime connectivity, trade, and interactions. The legacy of maritime sites was destroyed due to ongoing erosion activities and causes irretrievable loss on the information about the maritime structure and activities preserved within the archaeological sites. The present study focuses on the region between Pondicherry and Vedaraniyam region which has received considerable attention by the archaeologist.
2. STUDY AREA The proposed study area found within the southeast coast of India, bounded by the Bay of Bengal in the east. It extends between Pondicherry in the north and Vedaraniyam in the south, and lies between latitudes 11 ° 54’ N to 10 ° 16’ N and longitudes 79 ° 49’ E to 79 ° 49’ E. The length of the seashore of the study area is 243km (Fig 1).
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Figure 1 Location Map of the Study Area
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2.1. Archaeological Sites Arikamedu is an archaeological site in Southern India, in Kakkayanthope, Ariyankuppam Commune, and Puducherry and falls in between latitudes 11 ° 53’ N and longitudes 79 ° 49’E (Fig 2). It is located within 4 kilometers from the capital, Pondicherry of the Indian territory of Puducherry. The site was identified as the port of Podouke, known as an "emporium" in the Periplus of the Erythraean Sea and Ptolemy ( Begley el at., 1983) .
The Poompuhar port city established and nurtured by the Chola dynasty and maintained later on by Pallavas and Kalabras and remained as one of the leading ports of maritime history have become extinct around 2000-1000 Yr. BP.(?), (Soundar Rajan, 1994). The present Poompuhar is located within the latitudes 11 ° 09’ N and longitudes 79 ° 50’ E (Fig 3).
Sembiyankandiyur is an archaeological site in Nagapattinam district in Tamil Nadu , India and it falls between 11 ° 05’N latitudes and 79 ° 51’E longitudes (Fig 4). The artifact with the script found in this site was dated to 1500 B.C ( Subramaniam T.S., 2006) .
Tharangambadi, formerly Tranquebar is a town in the Mayiladuthurai district of the Indian state of Tamil Nadu on the Coromandel Coast . It lies 15 kilometers north of Karaikal , near the mouth of a distributary of the Kaveri River. Tranquebar was established on 19 November 1620 as the first Danish trading port in India ( IAR 1962 - 63) . It falls between 11 ° 01’ N latitude and 79 ° 51’E longitudes (Fig 5).
3. RESULTS AND DISCUSSION Analyses of changes in coastline were performed through Digital Shoreline Analysis System (DSAS) toolbar of Arc GIS. This allows classifying the coastal erosion and accretion pattern within the study area. Survey of toposheet and Landsat images were used to monitor the shoreline change along the study area coast for the period between 1972 and 2018. The causes and impact of surface changes were quantified along 66 transects. The process includes a comparison of historical shoreline (Andreson et.al.2017) through the perpendicular transects at 50 m intervals with a customized distance of 500m (Fig 2, 3, 4, 5). The quantified long-term rate of shoreline movement (LRR), short-term variation in shoreline (EPR) and net shoreline movement (NSM) along each transect were given in Table 1.
The result of the process highlights the Archaeological sites that have been experiencing a higher rate of erosion since, 1972. The combination of LRR, EPR and NSM forms significant information for the coastal archaeological risk assessment, which in turn useful in adopting suitable preventive measures. The results of shoreline changes along with the Archaeological sites Viz. Arikamedu, Poompuhar, Sembiyankandiyur, and Tharangambadi are given in Fig 2,3,4,5 respectively. The positive value of the long-term rate of shoreline movement (LRR) 6.14m in Arikamedu, 7.17m in Poompuhar, 5.02m in Tharangambadi, and 9.12m in Sembiyankandiyur (Table 1) results from the coastline with depositional / progradation trends. The shorelines dominated with erosion nature express the negative LRR values Viz. -1.39m in Arikamedu, Poompuhar, and Tharangambadi and -1.61 m Sembiyankandiyur.
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Figure 2 Shoreline change at Arikamedu Site
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Figure 3 Shoreline Change at Poompuhar Site
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Figure 4 Shoreline Change at Sembiyankandiyur Site
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Figure 5 Shoreline Change at Tharangambadi Site
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Table 1 Overall Shoreline Changes in the Archaeological site Archaeological site LRR EPR NSM -1.39 -2.01 -20.52 Arikamedu 6.14 7.84 45.66 -1.39 -2.01 -20.52 Poompuhar 7.17 9.27 53.2 -1.61 -2.48 -25.28 Sembiyankandiyur 9.12 9.83 56.38 -1.39 -2.01 -20.52 Tharangambadi 5.02 6.61 42.3
The short-term variation in shoreline (EPR values) for all the transects with respect to archaeological sites were calculated. The Positive EPR values representing accretion in the study area are 7.48m in Arikamedu, 9.27m in Poompuhar, 6.61m in Tharangambadi and 9.83m in Sembiyankandiyur. The negative EPR values of erosional coasts are -2.01m in Arikamedu, Poompuhar, and Tharangambadi and -2.48m in Sembiyankandiyur. The Net shoreline movement (NSM) statistics show that the coastal tracts of archaeological sites mostly prograded may be attributed to tropical cyclones effect. The NSM data points along each transect for the study period indicates erosional natures at Arikamedu, Poompuhar and Tharangambadi with -20.52m / period and -25.28m / period at Sembiyankandiyur.
3. CONCLUSION The result of the present study facilitates to generate baseline information about the prevalence of erosion / accretion processes in between Pondicherry and Vedaraniyam coastal tracts of Tamil Nadu. The LRR value -1.39m / year, EPR value -2.01m / year and NSM with -20.52m/period exposes the prevalence of erosional process in the study area irrespective of short-term, long-term, and net shoreline movement. On the other hand, the progradation values of LRR, EPR, and NSM were varied. This indicates that the progradation in the study area is influenced by the tropical cyclone. The similarity in the erosional values of LRR, EPR, and NSM reveals that the magnitudes of erosional processes are almost similar in the Arikamedu, Poompuhar, and Tharangambadi.
The Sembiyankandiyur LRR value of -1.61m/year, EPR with -2.48m/year, and NSM with -25.2m/period depicts that this region experiences more coastal erosion. The positive value of LRR as 9.12m/year, EPR as 9.83m/year, and 56.38m/period indicates simultaneous Progradation in this region. Sembiyankandiyur The archaeological site is more prone to shoreline oscillation when compare to the Arikamedu, Poompuhar, and Tharangambadi. The study warrants immediate attention to prevent the archaeological significant maritime port cities from the Coastal erosional activities.
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Acknowledgement The authors acknowledge the funding support of Department of Science and Technology - Interdisciplinary Cyber Physical Systems (DST-ICPS) – DST/ICPS/Digital Poompuhar/2017 (General) dated 14.03.2019.
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