Demarcating saline water intrusion pathways using remote sensing, GIS and geophysical techniques in structurally controlled coastal aquifers in Southern India

Application of remote sensing and geographical information system (GIS) with the help of ground truth studies like vertical electrical soundings (VES) and water quality measurements gave a comprehensive picture on saline water intrusion pathways in the structural controlled aquifers of Uppanar and Cauvery River systems located in Sirkazhi and Mannanpandal coastal areas of Southern India. The detailed geomorphic units and lineaments were mapped using IRS LISS-III (1:50,000 Scale) and SRTM Elevation Digital data under GIS environment. The area is mainly alluvial deposits of Holocene Age and classified into three major geomorphic units (i.e., fluvial, fluviomarine, and marine geomorphic units). The identified lineaments are mostly trending North-northeast (NNE)–South-southwest (SSW), Northeast (NE)–Southwest (SW), Northwest (NW)–Southeast (SE), East–West (EW) and East-Northeast (ENE)–West-Southwest (WSW) directions. Some of them are potential for fresh groundwater occurrence and movement. The lineaments trending NE–SW, NNE–SSW, and ENE–WSW act as pathways for saline water intrusion to the inland. The lineament L1 (NNE–SSW trending) conformed as a sinisterly shifted fault played a significant role in saline water intrusion. The area within the parallel lineaments L2 and L3 oriented ENE–WSW direction indicates low topography, beach ridges, paleo-channel sinuosity, large aerial extent of tidal flats, and backwater inundation. All the above geomorphic units gave indirect evidence of land subsidence, which was confirmed with the help of sub-surface geo-electrical signals obtained through VES and in situ groundwater quality measurements. Integrating all the above results, the saline water spread and fresh water pockets were identified.