Abstract
Aquifers along the coastal regions around the world are facing severe level of saline water intrusion problems. Rapid development and the associated increase in groundwater withdrawals intensify the problem. Extensive mapping of migration and extent of salt water plumes is difficult and costly. Several surficial geophysical methods have been developed for measuring salinity levels in coastal aquifers. The present study is an attempt to delineate the saline water and fresh water intrusion in parts of west coast of Maharashtra, India. A total of 86 vertical electrical soundings were carried out using the Schlumberger configuration. The contour maps for Dar-Zarrouk parameters viz. the transverse resistance (T), longitudinal conductance (S), and coefficient of anisotropy (λ) were computed at 84 sites to generate the resistivity regime of saline and fresh water bearing formations. The results exemplify that the Dar-Zarrouk parameters provide a practical elucidation in demarcating the saline and fresh water aquifers, particularly when the resistivity data interpretation encounters constraints due to intermixing of saline water aquifers, fresh water aquifers etc. Several NE-SW and NW-SE oriented major lineaments and its cris-crosses have been observed in this region.
Highlights
Saltwater intrusion can pose severe problems to coastal areas with freshwater aquifer having marine-aquifer hydraulic interaction
If the geologic sequence and clayey overburden is moderately thick, high longitudinal conductance is suggestive of better protective capacity of aquifers (Oladapo and Akintorinwa 2007)
The electrical conductivity (EC) values recorded at VES points 3.78 and 86 falls beyond the acceptable level for drinking prescribed by World Health Organization (WHO, 1984), and were attributed due to the intrusion of saline water from Arabian Sea
Summary
Saltwater intrusion can pose severe problems to coastal areas with freshwater aquifer having marine-aquifer hydraulic interaction. Saltwater intrusion happens when low density of fresh groundwater interacts with the high density of saltwater in natural conditions. Other sources of contamination include anthropogenic activity like domestic/industrial waste water and agricultural activities. In these studies, hydro-geochemistry analysis from monitoring wells and geophysical methods were used. The most widely used geophysical method to assign, in salinity mapping, is geo-electrical method (Loke, 2000). Various researchers around the world have applied geo-electrical method in demarcating coastal-area hydrogeology condition (Maiti et al, 2013; Gupta et al, 2014)
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