Assessment of Sub-surface Hydrogeology of Coastal Aquifer using Geophysical Technique in Sagar Island, West Bengal

The Vertical Electrical Sounding method is used in this study to discover the subsurface hydrogeology of Sagar Island. The major goal is to interpret the sub-surface formation and to identify aquifer features of this Island. The geophysical investigation that has involved the electrical resistivity method, indicates that all the major subsurface formations occur throughout the Island are extensive. In general, five major subsurface formations are interpreted. These are the top highly unconsolidated sediments underlain by a saline water zone comprising clay, silt and sand lenses continuing to a depth of 21–34 m. Below this, a brackish water zone occurs within 21–150 m depth, which is underlain by thick impermeable clay layer. Further down, fresh water aquifer occurs within fine and medium sand layers. To circumscribe the brackish water-fresh water zones and to illustrate the groundwater potential zones, Dar-Zarrouk parameters are estimated such as longitudinal conductance, transverse resistance, average longitudinal resistivity, average transverse resistivity, coefficient of anisotropy. It is also found that the southern section of the region has extremely high transverse resistance and more promise than that of northern part in this study region. The analysed data of coastal aquifer characteristics like hydraulic conductivity and transmissivity is found as 5.619–15.493 m/day and 1571.44–4555 m ² /day respectively. Spatial variation maps of aquifer parameters are also prepared using geospatial software.