Study on Saline Water Intrusion into the Shallow Coastal Aquifers of Periyar River Basin, Kerala Using Hydrochemical and Electrical Resistivity Methods

Abstract

Seawater intrusion generally occurs when withdrawal of fresh groundwater from coastal aquifers results in declining groundwater levels, facilitating lateral and/or vertical migration of saline water causing deterioration of groundwater quality. Electrical resistivity sounding techniques and hydrochemical studies are widely used to determine the interaction between groundwater and saline water/seawater in coastal aquifers. Vertical electrical soundings were carried out at 15 locations in the midland and coastal plain reaches of Periyar River basin in central Kerala, India (9° 55′-10° 20′ N latitude and 76° 05′-76° 25′ E longitude) using CRM 500 model aquameter. In-situ water quality parameters of water samples from 63 shallow well were also measured using handheld multi-parameter instrument. The cation and anion content of selected water samples (32 nos.) were also determined. Electrical resistivity profiles were interpreted qualitatively and quantitatively to obtain nature and thickness of different resistivity layers. The depth to fresh-saline water interface was delineated from resistivity model. The study indicates majority of the curves obtained are Q type with 3 layers. The depth to saline-fresh water interface varied from <1 to 5 m at different locations. The high salinity clay horizons are identified at various depths. Hydrochemical data was analysed using hill-piper diagram and statistical plots to understand groundwater-seawater mixing/interaction in the coastal aquifers. The dominant groundwater type is Na-Cl followed by Mg-Cl at few places. Higher pH, EC and TDS is noted in the western part towards seaward side. Turbidity levels are found increasing towards the southern part. The TA, TH, Ca2+,Mg2+,K+ content of the water samples found increasing towards southwest parts. The Na+, Cl− and (SO4)2− content is found higher in the northwestern parts.