Resistivity Characterization of Aquifer in Coastal Semiarid Areas: An Approach for Hydrogeological Evaluation

In coastal and semiarid regions, the scientific interest lies in imaging the saltwater intrusion and delineating freshwater aquifer zones, respectively. Direct current resistivity (DCR) and induced polarization (IP) geophysical methods are commonly used to assess hydraulic characteristics of the aquifer. Particularly, the main reason for hydrogeophysical application of both DCR and IP is that the electrical characteristics of aquifers depend mainly on the geometry of the pore space and the porosity controlling the soil and rock effective transport properties. For preliminary hydrogeological investigations, these methods are applied at a wide range of field and laboratory scales. Accordingly, the vulnerable zone to the saltwater intrusion and/or contamination can be characterized by high accuracy. Furthermore, empirical and semiempirical relationships are widely used to predict the aquifer petrophysical characteristics, e.g., hydraulic conductivity, using the inversion results of such electrical methods. Equally, conventional and nonconventional DCR inversion algorithms are developed to reduce the nonuniqueness problem of actual resistivity interpretation and, consequently, to obtain more meaningful models than previously reported. As case histories, this chapter demonstrates the efficiency of DCR method for hydrogeological assessment in Nile Delta, Egypt, emphasizing on technical constraints to achieve sustainable development in coastal and semiarid areas.