Abstract:
Groundwater quality and the water table behavior at Weligama Bay have been
studied in the aftermath of the Tsunami. 90 affected shallow dug wells, situated on a
8 km coastal strip, were selected for the study. The wells are sunk into the
permeable quaternary sand deposits overlying precambrian granite gneiss. The top
quaternary sandy aquifer in the coastal margin at Weligama Bay is very permeable
and hydro-geological conditions are very favorable for saltwater intrusion. The study
helped to prepare the hydro-geological and the hydro-geo-chemical maps of the
area.
Prior to the Tsunami, water of these wells was non-saline and used by the
people for drinking and other domestic purposes. The preliminary results of the study
revealed that the electrical conductivity (EC) of wellwater in all wells situated in the
Tsunami-affected region have become saline; the EC values, on average, increased
from 300 to around 1300 μ Siemens/cm). Total dissolved solids of the wellwaters
were around 1.000 mg/l.
It can be concluded that the underground pressure wave which has likely
developed due to the Tsunami may have disturbed the freshwater-saltwater
equilibrium resulting in the mixing of fresh groundwater with saline water.
