Impact of the 26-12-04 tsunami

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• Topography:Mountainous with small coastal planes
• Geology: Range of mountains of Tertiary Marine Sedimentary rocks and Late Cretaceous igneous rocks. There is coral along the coasts everywhere. Alluvial sediments in low areas.
• Hydrogeology: Groundwater is a major water source. The best aquifers are found in the coralline limestone and the alluvial sediments.
• Vulnerability: Intrusion of saline water during the tsunami flood is expected in low sandy areas; Previously fresh groundwater resources may be saline due to changes in shorelines
• Damage areas: Nicobar Islands suffered most of the damage. Much damage also on the east side of South Andaman.
  The topography of the Andaman and Nicobar Islands have been quite dramatically altered - shorelines have shrunk, beaches have been washed away and in some instances, islands have been split into separate bodies.
• Water supply: The CGWB reports that improvement in water quality is achieved due to natural flushing because of rain as well as pumping for long hours. Many wells which got damaged are yet to be reinstated. The ground water sources in the high land areas remained unaffected due to Tsunami. Geophysical studies carried out in Little Andaman and Car Nicobar Island has indicated a shallow saltwater/freshwater interface and therefore dugwells are the only feasible structures. In Little Andaman at many places in the limestone terrain a reduction is observed in spring discharges, while in some places an increase in spring discharges has been observed.

(information from http://www.cgwber.nic.in/andaman.htmand http://tsunamiandaman.tn.nic.in)

• Topography: width of coastal plain varies from about 1 km to more than 10 km Large flat areas near the coast are found in de delta of the Cauvary River near Nagappattinam and in the area north of Madras
• Geology: coastal plain with alluvial sediments and coral reefs; alluvium mainly clayey but sandy parts also exist
• Hydrogeology: shallow alluvial phreatic aquifer pumped by private open dug wells; deep sandy alluvial aquifers are situated more inland, pumped by tube wells for public water supply; at Pondicherry aquifers along the coast are overpumped and suffer from seawater intrusion.
• Vulnerability: Intrusion of saline water during the tsunami flood is expected in the permeable sandy sediments; in some areas stagnant water remained, increasing the period of intrusion; retreat of coastline will cause inland movement of salt water interface
• Damage areas: see map
• Water supply: over 1,500 wells were contaminated with salt water; new tubewells are sited and drilled
• Remarks: The CGWB reports that open wells and tubewells adjoining the sea shore within 300-500 m., turned saline because of inundation and flooding of sea water. Subsequently, it has been observed that there is improvement in ground water quality due to natural flushing as well as heavy pumping of these wells to restore water supply. UNICEF is working with the Government to establish water quality monitoring

• Topography: in the northern and southern part large width of coastal plain, in the middle part coastal plain is narrow
• Geology: alluvial sediments stretch all along the coast, mainly clayey but sandy parts also exist; the thickness varies from a few meters to hundreds of meters
• Hydrogeology: shallow alluvial phreatic aquifer pumped by private open dug wells deep sandy alluvial aquifers are situated more inland, pumped by tube wells for public water supply
• Vulnerability: Intrusion of saline water during the tsunami flood is expected in the permeable sandy sediments;
• Damage areas: effect less than in Tamil Nadu; 300-800 meter inland; Water entered some towns
• Water supply: wells are located inland and were not affected
• Remarks: water samples show no increase in salinity

• Topography: in the northern and southern part narrow width of coastal plain, in the middle part coastal plain is wider, with a large lake near Cochin
• Geology: coastal plain with alluvial sediments and coral reefs; alluvium mainly clayey but sandy parts also exist
• Hydrogeology: shallow alluvial phreatic aquifer pumped by private open dug wells deep sandy alluvial aquifers are situated more inland, pumped by tube wells for public water supply
• Vulnerability: Intrusion of saline water during the tsunami flood is expected in permeable sandy sediments;
• Damage areas: see map
• Remarks: The CGWB reports that open wells and tubewells adjoining the sea shore turned saline because of inundation and flooding of sea water. Also here, improvement in ground water quality has been observed due to natural flushing and pumping.

(information from UNDP and WHO)

(Ref.: Geological map of India, 6th ed., 1:2,000,000, Gov. of India, 1963)

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