Assessment of spatial and temporal behavior of saline groundwater in a coastal aquifer: A case study from the Pungudutivu Isand, Sri Lanka.

Abstract

Miocene limestone aquifer is the only source of water for drinking, domestic and livelihood purposes in the Jaffna peninsula and its neighbouring islands. Groundwater resources are increasingly becoming scarce in these areas due to deterioration of groundwater quality. Severe water scarcity due to salinisation of groundwater is the major problem in the study area, in Jaffna and imposes limitations on lives and livelihoods of the people. Current freshwater supplied via waler bowsers are unable to fulfil the water requirements but have imposed water pricing on the local economy.

The present study is focused on demarcating fresh and saline groundwater bodies in the island and their spatial and temporal behaviour. 1600 wells were brought under initial monitoring to study the nature of water, whereas 36 representative sample localities amongst them were brought under monthly monitoring for Well-head and chemical parameters such as groundwater table depth, Electrical Conductivity (EC). Temperature, Total Dissolved Solids (TDS), Salinity, pH, HCO, and CT ions for a period of one year.

The study reveals that fresh groundwater resources are extremely scarce in the Pungudutivu Island where a majority of the wells (95%) are subjected to high salinity in the long dry season. Freshwater with an EC <1000 µS/cm are not found in the dry season and do not show a significant improvement in water quality even with the annual rains showing that only 14% of wells fall below EC < 1000 µS/cm in the wet season.

The flat and low elevated landscape with low elevated groundwater table and highly porous geological formations facilitate salinization of groundwater allowing mixing of sea water. Salinisation does not show any marked patterns either with local geology or land use. Detailed investigations are required to justify the sources and recommend appropriate remedial measures for sustainable livelihood development in the island.