Estimation of hydraulic characteristics from electrical resistivity data in coastal aquifers of southern India

Abstract

The applicability of geophysical techniques has been examined for evaluating aquifer properties like transmissivity and hydraulic conductivity of coastal aquifers, Tuticorin, Tamil Nadu. The pumping test data of 10 wells are interpreted by using forward modelling to obtain the aquifer characteristics in the study area. The available vertical electrical soundings (VES) data in the vicinity of the sites of pumping test have been interpreted; and true resistivity and thickness are determined at each site in the study area. Empirical relationships are established for estimating the hydraulic parameters from the electrical data.

The area under study is divided into three major geological formations viz. Archaean (hard rock), Tertiary and coastal sediments. The empirical relationships have been shown (1) between formation factor and hydraulic conductivity; (2) between transmissivity and transverse resistance and (3) between aquifer resistivity and hydraulic conductivity, in three different geological formations. The result shows a linear relationship between hydraulic conductivity and transverse unit resistance and between hydraulic conductivity and formation factor. These relations are further used to estimate the hydrogeological parameters viz transmissivity and hydraulic conductivity at remaining 18 vertical electrical sounding points, where pumping test data is not available. The hydraulic properties of aquifer at different points are then used to generate the corresponding contour maps. The thematic maps are finally utilized for the selection of suitable well sites in the study area using the electrical and aquifer parameters. The results indicate that the hard rock formation near the coast ofTuticorin is the most potential zone of groundwater for future exploitation.