Application of RS and GIS in Damage Assessment and Rehabilitation of 26th December 2004 Great Indian Ocean Tsunami Event in Car Nicobar Island, India4.5 Sediment Deposits The team surveyed beach profiles to document erosion (common near the coast) and deposition (common inland) by the tsunami. Sand eroded from beaches probably provided much of the sand that was deposited inland. The survey team dug trenches in the tsunami deposits to measure their thickness and to examine other characteristics that can shed light on how high the waves were and how fast the water was flowing. Data from the sediment deposits will not only reveal about the recent tsunami but also help them recognize and interpret the deposits of ancient tsunamis, which, in turn, will help them better understand an area’s tsunami history and its likely tsunami risk. The Kakana beach and Aukchung beach are selected for the study. The sand deposit is 2.5 m at Aukchung beach and 1 m at Arong beach (Fig 6).  4.6 Coastal Subsidence The subsidence observed at beaches near Malacca Jetty is 0.75 m and a temple on Malacca beach which is submerged by 1-1.25 m approximately (Fig 7). It is inferred from the observation that the subsidence may be a result of an earthquake (mega thrust caused the rise of sea floor and subsidence at beach). It is also predicted by the model used by USGS survey of Sumatra that the type of earthquake that caused the tsunami—a megathrust—will raise the sea floor above the fault rupture and cause subsidence near the coast. The pre and post tsunami images have been studied for the observation of subsidence.  4.7 Erosion and Coastal Response The Car Nicobar Island underwent significant modification by the tsunami. The shoreline eroded, beach sand was carried inland, and the coastal plain was flooded. Compared to the erosion and deposition of sediment by the tsunami that occurred relatively quickly, within hours of the initial tsunami impact, coastal subsidence resulted in additional erosion and shoreline retreat during the weeks and months following the tsunami. The observations from the field studies indicate coastal erosion at Aukchung, Kimus and Malacca villages where the road is washed off, Mangroves and bridges (Fig 8) are damaged and underwater cracks extended inward where the high tide water is filled up. In addition, some parts of beaches have new sand deposition, located near Aukchung and at me places near Kakana where the beaches started rebuilding as soon as a few weeks after the tsunami, probably adding sand from nearby offshore. These reformed beaches were migrating landward through over-wash processes. Some beaches were still migrating landward, impacting roads and redevelopment plans for coastal villages. It is expected that the future shoreline retreat may continue to impact redevelopment in some areas.  4.8. Assessment of the Damages In order to assess the damages caused by the Great tsunami in the Car Nicobar Island the pre and post tsunami satellite data are critically analysed in the GIS domain. For this a base map is generated from the SOI topographic map of the region. The Base Map is later on updated from the field data and information obtained from the Nicobar Island Administration office. Based on this map the coastal area of the two scenes (pre and post) have been classified and vectorised using the ERDAS vector and ArcView software (Fig 1). Overlay analysis of these classified vector data is performed to find out the changes in the coastal corridor of the Island and ultimate the assessment of the damages is done form this analysis. The result of the assessment is tabulated as below (Table 1).  The Great Indonesian Earthquake of 26 December 2004 and a subsequent Great Tsunami event has led to the wide spread devastation in the Indian Ocean coast and all islands in its vicinity. These events have created ways and means to explore the nature’s mystery of natural processes/hazards in the Indian Ocean. The damages caused by these hazards are being accounted to the losses of millions of dollars and loss of property and life of people and many more homeless. The application of High resolution Remote Sensing data and GIS techniques are used to assess the tsunami hazards in the Car Nicobar Island. Maximum tsunami wave height was 15 meters of the SE pats of the island and minimum of 0.7 meters with a distance from the shore line of 400 meters and 368.58 metes respectively. The run up levels varied from 2-19 m and penetration distance from the coast, ranges from 295.87-1202.57 m on the inland. The tsunami water flowed from all the directions to the island. A considerable part of all the existing beaches hosting mostly infrastructural, commercial and residential complexes have been fully damaged. The sand deposits at Aukchung and Arong beaches are 2.5 and 1 meter respectively. The coastal subsidence near Malacca Jetty is 0.75 m and a temple on Malacca beach is 1-1.25 meters. The car Nicobar Island underwent significant coastal modification and the over all coastal area affected by the tsunami is 2075.26 ha. The study indicates considerable coastal erosion at Aukchung, Kimus and Malacca villages. ACKNOWLEDGEMENT The financial assistance provided under the DST grant No. SR/S4/ES-135/3.5/2005 is thankfully acknowledged. The authors are grateful to A&N Administration for their help during the field work. 
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