Delineation of Groundwater Potential Zones in Deep Midland Aquifers Along Bharathapuzha River Basin, Kerala Using Geophysical Methods

Abstract

The occurrence and movement of groundwater especially in fractured bedrock aquifers in a given area is governed by many factors viz., topography, lithology, geological structures, fracture density, aperture and connectivity, secondary porosity. The study is an attempt to delineate groundwater potential zones in deep midland aquifers along the Bharathapuzha river basin, Kerala, India. The study area (∼ 840 km2) is part of the Bharathapuzha river basin (10̊ 40′-10̊ 50′ N latitude and 76̊ 05′-76̊ 30′ E longitude), is mainly underlain by massive Charnockite/Charnockite gneiss type of rock formation. Vertical Electrical Sounding data collected from 66 locations was interpreted qualitatively and quantitatively to obtain layered resistivity parameters and potential fractured zones in the deep aquifer. Thematic maps of drainage, geology, geomorphology, slope and lineaments were prepared using toposheets and IRS P6 LISS III imagery. Slope map shows steeper slopes in the southern and northeastern part of the study area. Dendritic to sub-dendritic drainage pattern is dominant in the area, is often controlled by lineaments and fault zones. Qualitative interpretation of vertical electrical sounding (VES) data shows multi-layered profiles in most of the locations (> 4 resistivity layers). Out of 66 VES curves, 24 nos. are 5 layered, 23 nos. are 6 layered, 17 are 7 layered and 2 are 4 layered. Resistivity of first layer varied from 11.9 Ωm (VES-37) to 8089 Ωm (VES-3) and thickness varied from 0.78 m (VES-37) to 4.79 m (VES-64). Resistivity of second layer varied from 35.3 Ωm (VES-3) to 11382 Ωm (VES-11) and thickness varied from 0.364 m (VES-11) to 11.3 m (VES-59). Bore wells of moderate to high yield tapping the deep aquifer zones are mainly located along lineament intersections.