Application of Remote Sensing for Damage Assessment of Coastal Ecosystems in India due to the December 2004 Tsunami

Abstract

Tsunami struck the Indian Coast including the Andaman and Nicobar Islands and the mainland coast on December 26, 2004. The tsunami ‘run up’ have significantly affected the coastal ecosystems on the Andaman and Nicobar Islands. Its effect on the mainland coast was less pronounced. Satellite data along with few ground surveys were used to assess damage to various ecosystems. Pre- and post-tsunami satellite data, mainly RESOURCESAT-1 AWiFs were used for the preliminary assessment. IRS LISS III and LISS IV data were also used in few cases. The impact on major ecosystems, such as mangroves, coral reef, sandy beaches, mudflats, tidal inlets, saline areas, forest, etc. was studied. The damage to ecosystems was categorized in to two types, total loss and degradation of ecosystems.

Mangroves of the Andaman and Nicobar Islands constitute about 18 per cent mangroves of the country. It was observed that the mangroves facing sea have undergone severe destruction. The mangroves have been eroded and trees have been uprooted. The mangroves along the creeks have been less damaged. Many mangrove areas remained submerged for a long time and thus destroyed. In the Andaman and Nicobar Islands, about 4700 ha mangroves were totally lost, while 10800 ha were damaged.

The giant tsunami waves smashed and crushed the reefs, while the backwash deposited the debris on the reef flat. The deposition of material killed the live coral colonies. It has been estimated that the Andaman and Nicobar Group of Islands lost reefs of about 50000 ha. About 11300 ha of reefs on the Andaman and Nicobar Islands were covered by sand, mud or detritus. The reefs of the Gulf of Mannar (south-east coast of India) have been affected marginally.

Most beaches have been affected on Islands and on the mainland coast. Few beaches have been washed away. On many beaches, sand has been deposited on the backshore. The nesting beaches for the endangered leatherback turtles that visit the Great Nicobar Island have been seriously damaged. On the mainland, sediments got accumulated on backshore in all tsunami-affected area. The deposition of heavy minerals, mainly ilmenite and garnet, were seen along the parts of the south-east and south-west Indian coasts. At few places, barrier islands/beaches were breached, on the south-west coast while the sand dunes were affected on the south-east coast. The tidal inlets on the mainland coast have either opened up or closed. In some cases, location of tidal inlets has also shifted. The lagoons have been contaminated by high saline water. Large tracts of land have become saline in the Andaman and Nicobar islands. About 25000 ha have been affected by salinity. Significant loss of forest, about 12000 ha was noticed on the Nicobar Islands.

The damage to ecosystem is critical as it directly affects livelihood of coastal communities. The enormous damage to the two vital ecosystems, especially the coral reef and mangroves, has affected the fishery resource in the area. Apart from some of the important species such as saltwater crocodiles, leather-back turtles and Megapode birds have been adversely affected.