Hydro-geophysical techniques for safe exploitation of the fresh groundwater resources in coastal area

Abstract

Vertical disposition of the freshwater aquifer lens and their progressive change on lateral scale are relevant to understand the short circuiting of fresh and saline water at coastal areas. Since, half of the world population dwells within 50 km of coast line, the freshwater aquifers at coast are deteriorating at alarming rate. There are well-defined water well construction plans for coastal aquifer management, but mostly fails while execution due to lack of precise knowledge of subsurface lithological layer setup. In the present study, an attempt has been made to investigate such precise information about subsurface lithological layer setup to protect the freshwater resources at coastal area, applying noninvasive hydro-geophysical technique. Integrated electrical parameters, hydrochemistry, topography, and water table assessment have been applied to decipher the geometry of freshwater lens at Cuddalore coast, India. Results show in this study (1) the electrical resistivity (ρ) 1–10 Ω-m of subsurface formation, electrical conductivity (σ) 30,891 µS/cm of groundwater, and water table 1.55 m above mean sea level (MSL) confirms the zone of effluent contamination; (2) the zone showing ρ = 1–10 Ω-m, σ = 6172 µS/cm, water table 6.46 m below MSL is attributed to the saline water intrusion; (3) freshwater formations are identified in beach ridges underlain by clay layers with ρ = 30–60 Ω-m, σ = 453 µS/cm and water table above MSL; and (4) water well design is proposed to tap the freshwater aquifers avoiding vertical short circuiting of saline and freshwater.