Monitoring Coastal and Seafloor Changes in The Gulf of Mannar, Southeast Coast of India Using Remote Sensing and GIS TechnologyM. Thanikachalam Assistant Professor, Department of Civil Engineering, Adhiyamaan College of Engineering, Hosur-635 109 aisuwariyaa@yahoo.com V. A. Kumaresan Professor & Head, Department of Civil Engineering, Adhiyamaan College of Engineering, Hosur-635 109 S. Ramachandran Director, Center for Research, Anna University, Chennai-600 025, INDIA ABSTRACT Three kinds of approach was attempted to identify the changes of coastal and off-shore morphology of the Gulf of Mannar. Survey of India (SOI) topographic map (1969) and IRS LISS-III (1998) satellite data are used for shore line change and coastal land form mapping. Multi-date bathymetry data (1975 and 1999) are used for bathymetry mapping and identify the seafloor change. The multi-date shoreline date analysis indicates that 23.49 km2 and 4.34 km2 of the mainland coast and 3.3 km2 and 4.10 km2 of island coast have been accreted and eroded over a period of 30 years (1969-1998). The multi-date bathymetry data analysis indicates that the 0.51m sea floor depth have been decreased all along self region of the Gulf of Mannar. Seaward migration of shoreline, newly formed spits, swales, beach ridges, mudflat, strandlines and reduction of seafloor depth indicates that the Gulf of Mannar sea floor have been rising by tectonic movement. INTRODUCTION The coastal environment is very dynamic with many cyclic and random processes owing to a variety of resources and habitats. It play a vital role in nation’s economy by virtue of their resources, productive habitats and rich biodiversity. India has a coastline of 7,516 km and nearly 250 million people live within a distance of 50 km from the coast. The coastal zone is endowed with a variety of coastal ecosystems like mangroves, coral reefs, lagoons, sea grass, salt marsh, estuary etc. Coastal ecosystems are important for millions of people around the world as they provide subsistence. The coastal ecosystems are now highly disturbed and threatened due to rapid increase of population and developmental activities along the coast. In the state of Tamil Nadu, between the year 1988 and 1998, 25.56 km² of coral reefs and 2.16 km² of seaweeds were lost in Gulf of Mannar (Thanikachalam and Ramachandran 2002a, 2002b, 2002c and 2003). Between the year 1986 and 1993, 0.36 km² area of mangrove in Pichavaram was lost and nearly 2500km² of the mangrove were lost in entire India between 1986 and 1994 (Krishnamoorthy 1995). Apart from the anthropogenic activities, natural causes are also play an important roll in coastal environment changes. Current approaches to the monitoring and management of coastal ecosystem are not capable for sustainable development. The modern scientific tools of remote sensing, GIS and GPS are extremely valuable in coastal environmental studies. Availability of repetitive, synoptic and multi-spectral data from various satellite platforms, have helped to generate information on varied aspects of the coastal and marine environment (Nayak 2002). The present study has been attempted to monitor coastal and seafloor changes of the Gulf of Mannar, using remote sensing and GIS techniques. STUDY AREA Gulf of Mannar (Figure1), extends 140 km in the SW-NE direction between 78º 5’ and 79º30’ E longitudes and 8º47’ and 9º15’ N latitudes and it covers an area of about 10, 500 km². There are 21 islands, situated at an average distance of about 8 km from the coast and running almost parallel to the coastline. The Gulf of Mannar is endowed with a combination of ecosystems including mangroves, sea-grass, seaweed and corals reefs. Gulf of Mannar exhibits various types of reefs such as fringing, patch, and coral pinnacles. The coast of Gulf of Mannar is mostly underling by Quaternary to Recent formation. The west of this coastal area is bound by heavy crystalline metamorphic rocks of Pre Cambrian and having breath of 10-100 km (Ramasamy 1997). Being a gradient coast it has developed well fabricated network of deltas, backwater, creeks, protruding deltas, estuaries, back swamps and coral reef etc. In 1989 Gulf of Mannar was declared as a Marine Biosphere Reserve jointly by the State Government of Tamil Nadu and the Government of India.  Figure 1. IRS LISS-III Imagery of Gulf of Mannar (Study Area) MATERIALS AND METHODS Three types of approaches have been attempted in the study (1) analysis and interpretation of optical remote sensing data (IRS LISS-III 1998) for coastal land form mapping, (2) analysis of the multi-date bathymetry data for see floor changes (NHO Chart, 1975 and ground truth studies, 1999), (3).analysis and interpretation of optical remote sensing data (IRS LISS-III 1998 data) and Survey of India Topographic sheets (1969) for shoreline-change mapping. Coastal Geomorphology Mapping Geocoded IRS1D LISS – III imagery on 1:50,000 scale were visually interpreted based on image characteristics, and various coastal geomorphic categories were identified and mapped along the coast of Gulf of Mannar. In the present study, an image interpretation key indicating tone/colour, size and pattern developed by Space Applications Center, Ahmedabad SAC 1991), was mad. The basic information like transport network, tanks, rivers etc are transferred from SOI toposheet. After identification and delineation, an accuracy test was made for 118 sample points on SOI toposheet. The study area map was divided into grids and intersecting points of each grid within the study area were taken as sample points for validation of classified satellite data in ground truth checking. Over the ground, out of the 118 sample points, 105 points were found to be correctly interpreted giving an accuracy of about 90 per cent. The georeferenced geomorphology map was digitized, edited, labeled and projected using ARC-INFO GIS. Finally a coastal geomorohology map was generated using intercept operation of ARC/VIEW. The area statistics of coastal geomorphology in the map were generated.
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