Tsunami impact on shallow groundwater in the Ampara district in Eastern Sri Lanka: Conductivity measurements and qualitative interpretations

On 26 December 2004 a massive earthquake registering 9.0 on the Richter scale struck off the coast of Sumatra, Indonesia. This was followed by one of the most important tsunamis in history, with an impact on the coastal area of nearly 15 countries. In Sri Lanka several thousand shallow wells were damaged and polluted by salt. The east coast of Sri Lanka was strongly affected during the tsunami. Many wells were damaged because of the intrusion of salt water. In order to determine the boundaries of the well area affected by salt and the long-term evolution of the salt concentration in the aquifer, an experimental study of conductivity was carried out. The mapping of the conductivity wells shows that conductivity is high only in the area directly affected by the wave. Data analysis shows that there is a slow natural recovery process, reducing conductivity. The process is a combination of the downward gravity flow of salt water combined with a lateral fresh water flow toward the sea, but this remains a local phenomenon with different behavior of wells in apparently similar situations.