Conjunctive Use of Geophysical and Geological Data in the Study of an Alluvial Aquifer

Abstract

A geoelectric survey, composed of vertical electrical soundings, was conducted over part of the lower Platte Valley alluvial aquifer of east‐central Nebraska. Survey results, in conjunction with seismic‐survey data and test‐ hole‐log information, provided the basis to map the areal extent and thickness of a near‐surface, low‐permeability clay unit. Because of the low hydraulic conductivity of the clay, the unit forms a confining layer over a significant part of the aquifer. Generally, the approach to evaluating the lower Platte Valley alluvial aquifer for sustained yield has been to assume that the entire flow system is under water‐table conditions. However, numerical‐model simulations with and without the clay unit indicate that this confining layer has a significant effect on the hydraulic behavior of the groundwater flow system under pumping stresses. An estimate of the bulk porosity of the aquifer was made by using geoelectric data and applying the Archie equation. Values of porosity ranged from 0·27 to 0·43; although reasonable for fluvial sand and gravel, the range is higher than previous estimates.

Estimation of Aquifer Transmissivity Using Dar Zarrouk Parameters Derived from Surface Resistivity Measurements: A Case History from Parts of Enugu Town (Nigeria)

“…While dealing with basic equations of direct current prospecting, [34] observed that if one considers a geologic column built on a square unit (Figure 1), R is the resistance to the lines of current perpendicular to the strata, and, C is the conductance to the lines of current parallel to the strata. These theoretical relationships showing direct and inverse correlation between hydraulic conductivity and electrical resistivity has been explained with respect to four basic assumptions [5,6]: 1) In the case of a conducting basement, the hydraulic conductivity is directly proportional to the electrical resistivity: this applicable to Equation (1) ( Figure 2); 2) In the case of a resistive basement, the hydraulic conducting is inversely: this is applicable to Equation (2) (Figure 2); 3) In the case of an unconsolidated, sandy, clay-free aquifer, the hydraulic conductivity is directly related to the porosity [36] and inversely related to the electrical resistivity: this is applicable to Equation (1); 4) In the case of a clay-rich aquifer, the relationship between porosity breaks down in a more a complex manner leaving clay content as the primary factor controlling hydraulic conductivity: this is applicable to Equation (2). As a condition in sandy clay free hydrogeological environment, Kρ can be considered constant; in clay-rich environment K/ρ should remain constant.…”

“…As groundwater becomes more important as a source of uncontaminated water, improved hydrogeological knowledge, new groundwater exploration technologies and data processing methods must be efficient to facilitate investigations and evaluation of groundwater resources [1,2]. Many investigation techniques are commonly employed with the aim of estimating the spatial distribution of aquifer parameters such as hydraulic conductivity, transmissivity and aquifer depth [3].…”

Application of Secondary Resistivity Parameters to Determine Potential Aquifer Horizon: Case Study of Basement Rocks of Hussara, Northeastern Nigeria

“…The electrode configuration adopted for this study is the Schlumberger array. In this method four electrodes were placed along a straight line on the surface such that the current electrodes distance AB is equal to or greater than five times the potential electrode distance MN [9]. For the linear symmetry array of electrodes (AMNB), the apparent resistivity given by Gruntorad and Karous [8] is:…”

Resistivity investigation for well-site definition around Barika Village, Southeast Sulaimany city, Iraqi Kurdistan region.

“…In most earth materials, electricity is conducted electrolytically by the interstitial fluid. The resistivity is controlled mostly by porosity, water content and water quality than by the resistivities of the matrix (Ayer, 1989). The main target is identification of the horizontal and vertical variations in lithology, which might lead to more structural information about the subsurface.…”