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Monitoring Changes in Seafloor Morphology Using Multi-date Bathymetry data: A Case Study of the Gulf of Mannar, Southeast Coast of India
4.2 Sea Floor Changes The sea floor depth contours with reference to chart datum (1975) measured at Tuticorin and Mandapam coasts during April 1999 are shown in the Figures 3. The variations of sea floor elevations to chart datum in the study area, measured along 10 transects that are perpendicular to shoreline with an interval of 250m are presented in the Figures 4a to 4d.  Figure 4. a) Sea floor changes at Tuticorin and Van Island b) Sea floor changes at Veppaloadi and Vilangu Shuli Island c) Sea floor changes at Marakkayarpattinam Coast d) Sea floor changes at Gundugul and Kursadi Island Recent depth contour map (1999) has been compared with bathymetry map of 1975; it reflects that the seafloor level decreased along the coastal and around the islands in the study area. It may be due to emerging of land due to tectonism. Many authors have reported that the coast of Gulf of Mannar is on an emerging phase due to tectonic movement (Foot, 1888; Ahmad, 1972; Stoodart and Pillai, 1972; Loveson and Rajamanicam, 1988; Ramasamy, 1989). Ramasamy, (1996), has build up a post collision tectonic model for the southern part of Indian and in which he has observed a series of geoenvironmental problems being caused due to such ongoing tectonic movement. In very few places particularly at river mouths and in island areas, the sea floor level has increased, which may be due to erosion caused by anthropogenic activities. The removal of corals in Tuticorin group of island by coral mining the depth has increased to about 1m (Thanikackalam and Ramachandran 2002). The average depth reduction of seafloor along the coast of the study area has been estimated as 0.51m over a period of 24 years. Assuming that the rate of change of depth of sea floor is uniform over a year, the rate of decrease of depth is estimated as 0.021m/year along the coast and 0.023 m/year around the island. |