Vulnerability assessment of coastal aquifer system for irrigation suitability — A classical approach from southern India

Abstract

The vulnerability of the shallow aquifer system for saline water intrusion has been evaluated using the classical tools at a coastal area, southern India. Groundwater samples (N=144) from Quaternary aquifer system within 25 km2 area in pre- and post-monsoon seasons were analyzed for major ion chemistry including Electrical Conductivity (EC). The hydrochemical parameters are examined applying classical irrigation suitability tools. Based on their weight percentages (ratios in meq/l) the dominance of cations and anions was established as Na-Cl and Ca-SO4 type. Results show that high hydraulic conductivity (10−2 to 1 cm/s) of the sandy aquifer enhanced the vertical recharge leading to major spatial distribution suitable for irrigation use in post-monsoon. The overexploitation of groundwater resources has generated reversal of hydraulic gradient enhancing salinity intrusion from marine sources in pre-monsoon. Further, the Differential Global Positioning System (DGPS) survey and water level measurements are assessed to demarcate the study area into zones of water table ‘above mean sea level (amsl)’ and ‘below mean sea level (bmsl)’. It was deduced that, the industrial effluent and seawater were the prime sources of groundwater salinity of water table ‘amsl’ and ‘bmsl’ zones, respectively. The area up to 600 m from marine source is found vulnerable which is falling under ‘Unsuitable’ category of irrigation classifications. The remedial measures are also framed to protect further extension of aquifer vulnerability for sustainable agriculture.