Hydrogeological condition and groundwater quality distribution in the tsunami affected Southern coastal area of Sri Lanka

Abstract

Groundwater monitoring in the tsunami affected southern coastal Weligama bay area was conductedduring May 2005 to July 2006 to determine the hydrogeological conditions and groundwater quality byselecting 90 dug wells where water level, electrical conductivity (EC), total dissolved solids (TDS)and pH was measured in monthly interval. The Weligama bay area is located in latitudes and longitudesof 80°22', 5°97'. The dug wells are sunk into the permeable quaternary sand deposits in the coastalmargin at Weligama Bay area is very permeable and-hydro-geological conditions are very favorablefor saltwater intrusion.

The study helped to prepare groundwater isograph map and the distribution ofEC, TDS and pH mapsusing the GIS package MAPINFO. Groundwater isograph map help to identify groundwater distributionof the coastal area of Weligama. There exist a closed relationship between topographical map &groundwater contour map.

The results of the study revealed that the Electrical conductivity of well water in all wells situated inthe Tsunami affected Zone are turned to be saline (EC in average increases from 150011 Siemens perem to around 4000 ~l siemens /cm.). According to the hydrographs prepared during the study period,unconfined quaternary aquifer ground water level intimately related to atmospheric precipitation. Thecharacteristic of the hydrograph provides a conclusion, that the recharge of unconfined ground waterin quaternary aquifer takes place during the period of monsoon rain and quality of ground water dueto tsunami has not changed specially.