Lateral and vertical mapping of salinity along the coast of Ghana using Electrical Resistivity Tomography: The case of Central Region

Abstract

Seawater intrusion into coastal aquifers is a worldwide problem causing water quality challenges in most communities along the coast, and has prompted many investigations into its occurrence, sources and age. However, there is still a major challenge when it comes to evaluating the spatial distribution of the problem in coastal aquifers towards groundwater management. Therefore, this study has employed electrical resistivity tomography technique to delineate both the lateral and vertical distribution of the salinity within some thirteen coastal communities in the Central Region of Ghana. The survey was conducted using the multiple-gradient array technique with the aid of a multi-electrode ABEM Lund Imaging System along selected traverses from the coastline into the communities. 2-D resistivity pseudo-sections generated from the survey data showed a unique resistivity distribution within each community, influenced by the underlying local geology and seawater intrusion. Low resistivity layers (< 50 Ωm), which may be associated with saline water saturated geologic formations, are observed within almost all the communities investigated at both shallow and deeper depths. The study also revealed that, seawater intrusion has affected freshwater aquifers in the communities by more than 5 km in-land from the sea and need to be tackled.