Application of RS and GIS in Damage Assessment and Rehabilitation of 26th December 2004 Great Indian Ocean Tsunami Event in Car Nicobar Island, India3 MATERIALS AND METHODOLOGY 3.1 Materials Used: Software — ArcView, ERDAS IMAGINE etc. Data — Survey of India (SOI) topographic Maps, Satellite imageries- IRS-IC LISS III (24 Feb. 1999), IRS-P6 (16 Feb. 2005 & 01 Feb. 2005), GPS-Garmin etrex & Garmin vista, Sony Handycam, Sony Digital still camera, High precision Oregon scientific Altimeter, Measuring tapes, Staff etc. 3.2 Methodology: The IRS P-6 satellite has been found to be very sensitive system in this regard. The tilting of camera to see the affected areas from an easterly path of the satellite has been proven to be of a high practical utility combined with wide viewing of these images, the information may play a significant role in mapping the tsunami efforts for sustainable development in the region. The digital analysis of the P6 digital satellite data was done by using the image processing software (ERDAS IMAGINE 8.4). The various steps have been followed in order to find out the best results in deciphering the precise delineation of the various tsunami affected areas as proposed objectives. It is observed that the image enhancement techniques with brightness contrast and break points have became very successful in delineating the inundation of tsunami water on the islands by acquiring the actual reflectance values from the satellite data. The natural colour simulation was done to map coastal features precisely. The coastal mapping was made by on screen digitization (Fig 1). The wave height, run up elevation, coastal erosion delineation and impact of damages was made by using the DEM/DTM. On the basis of the elevation data of the surface a Digital Terrain Model (DTM) creates topography by geometric surface in a computer environment. This method provides best approach (Alpar B et.al 2004) to a 3D terrain surface using elevation points which were defined on a horizontal plane, from various data sources such as measured data, topographic maps, bathymetric data and images. In the present study the DTM was produced from topographic maps and SRTM data and has a cell size of 22 meters. The field data of the various locations that were collected with the help of handheld GPS (Garmin etrex & vista) were used as overlay on the Digital terrain model to verify the tsunami wave height as well as the distance from the sea.  4 RESULT & DISCUSSIONS: There are number of observations by various workers on the characteristics of past tsunami hazards such as Yalciner et.al. (1999, 2000 and 2001), Altinok et.al. 1999; Musaoglu 2000; and International Coral Reef Initiative/International Society for Reef Studies (2005) that has provided a rapid assessment and monitoring are worth mentioning. In the present studies tsunami hazards are delineated and assessed by the various observations during investigations and the results have been finalized in the following manner: 4.1 Tsunami Wave Heights The tsunami wave height are measured based on the satellite imageries and the DEM generated using SOI contour and 1m SRTM data with a vertical resolution of +/-1m.On the basis of the elevation data of the surface a Digital Terrain Model (DTM) creates topography by geometric surface in a computer environment. This method provides best approach (Alpar B et.al 2004) to a 3D terrain surface using elevation points which were defined on a horizontal plane, from various data sources such as measured data, topographic maps, bathymetric data and images. In the present study the DTM was produced from topographic maps and SRTM data and has a cell size of 22 meters. The field data of the various locations that were collected with the help of handheld GPS (Garmin etrex & vista) were used as overlay on the Digital terrain model to verify the tsunami wave height as well as the distance from the sea. In order to assess the tsunami height on all the sides of island, four strategic locations were selected viz. North eastern (NE), North western (NW), South eastern (SE) and South western (SW) part. A maximum tsunami wave height was 15m on the south east and minimum is 0.7 m with a distance from the shoreline of 400 m and 368.58 m respectively (Fig 45-48 and Table 3-6). The photograph taken from a low altitude aircraft also depicts the evidences of tsunami wave heights and the distance from the shore on the SE part of island (Fig 49). The various indicators such as wave heights, water stains on the buildings, salt burnt trees and broken branches of the trees and debris on the trees are used in the field survey. The manual methods are used to assess the heights. The south-east facing coastlines near Malacca area were struck by the highest waves, some more than 15 m high. Waves that hit the north facing coastline of Mus and Passa were lower, about 8-10 m high, but the area’s low-lying land allowed those waves to penetrate far inland. It is observed during the survey that many two storied buildings are inundated by tsunami waves and trees have the debris carried by tsunami water (Fig 2). The hypothesis of tsunami height was made by measuring wave heights at intermediate points along the coastline and to collect additional data on sediment-deposit profiles (USGS, http://walrus.wr.usgs.gov/tsunami/sumatra05 /heights.html).Effort s were focused mainly around the very south-east end of island around Malacca, Kakana, Chukchucha, Lapathy and Kimus to collect data. Wave heights of 15 m (50 ft) at those sites suggest that the tsunami waves may have been 10 to 15 m high along the entire stretch of coast from Malacca to Kimus.  4.2 Run Up Elevation In general, the extent of vertical run-up of seawater during tsunamis depends on earthquake parameters, geographical location, velocity of tsunami waves and their frequency, near shore bathymetry, beach profile and land topography. Due to these parametric variations in various coastal areas including islands, the run-up levels and landward penetration characteristics of seawater were the location specific and varied within a location and even in an island. In the case of Nicobar Island the run up levels varied from 2 m to 19m and the distance of penetration from the coast ranged from 295.87 to 1202.57m (Fig 3b). Bilham et.al. (2005) have drawn the preliminary conclusions on the slip pattern of 26 Dec 2004 earthquake that due to high rate of slip in the southern 650 km of the 1300 km North –South rupture zone of 2004 Andaman-Sumatra earthquake, the principal tsunami was generated in the Sumatra area. Time lag between earthquake and land subsidence in Car Nicobar on 26 Dec 2004 which is estimated to be 15-20 min has been interpreted as the high rate of slip was in the Nicobar region resulting generation of near-field high tsunami (19m run up level) in this zone. The above parameters have caused the land subsidence at Nicobar Islands due to the earthquake. The run up levels recorded at Andaman groups of Islands were different due to the low sip rate, caused by the earthquake. Similar types of diversified results were observed in 26th December 2004 Tsunami affected coastal areas in Thailand, Indonesia and Sri Lanka. Run up levels varying from 0.3 to 32 m were recorded in Indonesia and from 2.5 to 10 m in Sri Lanka (Yalciner, et.al, 2005) and Seychelles (2.5m) . It is observed that the run up level was affected by the earthquake mechanism and resulted to different run up levels at different coastal areas. In case of Nicobar Island, the run levels were varied from place to place as shown in the Fig3.  4.3 Inundation Inundation distances in the island were so large that they were most easily measured from satellite images, where sediment deposited by the waves and vegetation killed by the saltwater are clearly visible (Fig 3). Satellite images show that such waves that struck many such villages Malacca, Kakana, Kimus and Mus located SE, SW and NE parts of the islands. Items broken and bent by the tsunami waves were used to determine flow directions. The team found that the large tsunami waves flowed around natural barriers, flooding lowlying areas behind them. The inundation is marked on Kakana beach and Kimus beach (Fig 4).  4.4 Tsunami Flow Direction The Car Nicobar Island has been affected by the water inundation. The Team found that the large tsunami waves flowed around natural barrier, flooding low lying areas behind them. Flow direction has been marked by number of indicators such as water mark on the walls of the buildings, trees, DEM, satellite imageries, items broken and bent by the tsunami waves were used to determine the flow direction. It is observed that Nicobar Island, being very near to the earthquake source, the tsunami water inundated from all the sides and flown towards the inland. The flow direction of the tsunami water was from all sides of the island (Fig 5).  |