Impact of the 26-12-04 tsunami

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• Topography: A coastal belt about thirty meters above sea level surrounds the island. Much of the coast consists of sandy beaches indented by coastal lagoons. In the Jaffna Peninsula, limestone beds are exposed to the waves as low-lying cliffs in a few places. In the northeast and the southwest, where the coast cuts across the stratification of the crystalline rocks, rocky cliffs, bays, and offshore islands can be found.
• Geology: The core of the island is composed of Precambrian crystalline rocks. The coastal plains in the west, east and south of the island are formed by sand flats and beach barriers. The low area in the north of the island is formed by the clayey and sandy sediments deposited by the Cauvary River system. In the past, the coral reefs that surrounded the southern coast served as buffers against erosion. But illegal reef breaking and coral mining, combined with negative impacts of tourism and development (sewage, agricultural pollution, physical damage) have greatly reduced the effectiveness of the reef barriers.
• Hydrogeology: Most people in rural Sri Lanka depend on wells for their drinking water. Along the coast groundwater is abstracted mainly through shallow wells dug in the sandy sediments of the beach barriers.
• Vulnerability: Intrusion of saline water during the tsunami flood is expected in the permeable sandy sediments and in porous limestone aquifers; in many areas stagnant water remained after the tsunami, increasing the period of intrusion; retreat of coastline will cause inland movement of salt water interface.
  Reports were received of geysers (of groundwater?) appearing from the ground just before the tsunami wave flooded the terrain.
• Damage areas: Fresh groundwater resources have been polluted by sea water along the east and south coast. The MUDWS estimated that 12,130 wells were damaged.
• Water supply: The water distribution network is partially damaged in some places and completely destroyed elsewhere. There is not only a scarcity of drinking water, but also a shortage of water for agricultural purposes. Most water purifying plants in the south have been damaged beyond repair. Decontamination of wells is going on by pumping.
• Monitoring: The Water Board has requested WHO to lead the implementation of a water quality monitoring system

Information from: scidev.net, USAID, USACE and WHO,

Ref.: Geological map of South and East Asia, sheet no. 3. 1:5,000,000,CGMW, 1990

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