Geoelectrical Sounding Data Research Articles

Modeling of aquifer using vertical electrical sounding data with kriging interpolation in Padang City

Aquifer is an underground layer of water. Currently, many residents of Padang do not know the exact position of the aquifer. Many drilling activities have been carried out to find ground water. But the results are not in accordance with the predetermined depth targets. This situation will be affected to the costs incurred for drilling. This study aims to model aquifers in Padang and find out their depth and thickness. One way to identify aquifers is to use geoelectrical resistivity method. In this study, researchers used a one-dimensional vertical electrical sounding (VES). The collection of geoelectrical sounding data is spread in 36 points in Padang. To modeling the aquifer layer, kriging interpolation method is used. Based on the results of processing rock resistivity models, it was found that the average aquifer depth in Padang is about 6.23 meters, with the shallow depth in 1.01 meters and the deepest in 20.02 meters. While the average thickness of aquifers is about 7.47 meters, with the thinnest thickness in 1.68 meters and the thickest in 11.74 meters. The aquifer layer was identified as unconfined aquifer.

Groundwater resource evaluation in the western part of Kushtia district of Bangladesh using vertical electrical sounding technique

Geoelectrical sounding, borehole litholog, and groundwater data have been used for the exploration of groundwater resources in the western part of greater Kushtia district, Bangladesh. This study aimed to delineate the boundary and the depth of aquifers, and assess their vulnerability to near-surface contaminants. Fourteen geoelectrical sounding data are interpreted and the corresponding geoelectrical logs are correlated with the available nearby horehole lithologs. Four distinct geoelectrical layers are identified within the depth of 105 m, namely thin topsoil (8.0–97.6 Ωm, 0.5–3.6 m), conductive clay-silt-sand layer (8.6–27.5 Ωm, 1.3–49.4 m), medium resistive fine grained aquifer (25.8–45.0 Ωm, 10.1–30.4 m), and high-resistive coarse grained water-bearing aquifer (35.0–64.9 Ωm, 30.0–76.9 m). The shallow aquifer (third layer) is found to occur at a depth ranging between 1.7 and 51 m, whereas the deeper aquifer (fourth layer) is found to occur within the depth between 14 and 52 m, both saturated with water. The groundwater resistivity and formation resistivity factor in the study area is found to vary from 15 to 30 Ωm and 1.93 to 2.68, respectively. The narrow low-protective layer has made the shallow aquifer highly vulnerable to surface contaminant in the study area.

Geo-electrical soundings and analysis to investigate groundwater aquifers at Khulna City, coastal area of Bangladesh

Geo-electrical soundings using the Schlumberger configuration were carried out in the coastal city srea of Khulna, Bangladesh, to identify different water bearing horizons within the coastal plain sands. Geo-electrical sounding data were interpreted by partial curve matching technique to obtain the initial model parameters. This initial model was then used to obtain the final layer parameters through inversion technique. The best-fitted models were correlated with the litholog. Results show that two major water bearing horizons exist in the area: (i) an upper zone consisting of fine grained sands having apparent resistivity of 2–10 Ω m and (ii) a lower zone consisting of medium to coarse grained sands with 6–38 Ω m apparent resistivity value. The resistivities for most of the aquifer zones are found to be very low, which may be due to the salinity of groundwater besides their packing and grain size.

Delineation of layer boundaries from smooth models obtained from the geoelectrical sounding data inversion

Two techniques have been presented for the delineation of boundaries from smooth models obtained by smooth inversion techniques of geoelectrical sounding data, such as straightforward inversion scheme, Occam’s and Zohdy’s methods. The smooth model consists of a large number of equally spaced layers, wherein the real geological boundaries are missing. The techniques proposed here suppress the geologically irrelevant boundaries and support the real structural boundaries present in the geoelectrical data. In the first technique, solution of linear inverse problem is improved iteratively through weighted minimum norm inverse, the weight being taken from the current solution. The technique is referred as Iterative Straightforward Inversion Scheme. The second method is analytical, based on the application of smoothing filter, referred in the literature as edge-preserving smoothing. A few examples of theoretical magnetotelluric, dc resistivity and field sounding data have been presented to demonstrate the capabilities of the techniques. The methodologies also reduce the conspicuous oscillations in the smooth solutions caused by the conversion of sharp boundaries to the smooth ones.

In situ measurements of the direct-current conductivity of Antarctic Sea ice: implications for airborne electromagnetic Sounding of Sea-ice thickness

AbstractAirborne, Ship-borne and Surface low-frequency electromagnetic (EM) methods have become widely applied to measure Sea-ice thickness. EM responses measured over Sea ice depend mainly on the Sea-water conductivity and on the height of the Sensor above the Sea-ice–sea-water interface, but may be Sensitive to the Sea-ice conductivity at high excitation frequencies. We have conducted in Situ measurements of direct-current conductivity of Sea ice using Standard geophysical geoelectrical methods. Sea-ice thickness estimated from the geoelectrical Sounding data was found to be consistently underestimated due to the pronounced vertical-to-horizontal conductivity anisotropy present in level Sea ice. At five Sites, it was possible to determine the approximate horizontal and vertical conductivities from the Sounding data. The average horizontal conductivity was found to be 0.017 Sm–1, and that in the vertical direction to be 9–12 times higher. EM measurements over level Sea ice are Sensitive only to the horizontal conductivity. Numerical modelling has Shown that the assumption of zero Sea-ice conductivity in interpretation of airborne EM data results in a negligible error in interpreted thickness for typical level Antarctic Sea ice.

Estimates of the relative specific yield of aquifers from geo-electrical sounding data of the coastal plains of southeastern Nigeria

This paper discusses a method of estimating aquifer specific yield based on surface resistivity sounding measurements supplemented with data on water conductivity. The practical aim of the method is to suggest a parallel low cost method of estimating aquifer properties. The starting point is the Archie's law, which relates porosity and degree of saturation to electrical resistivity derived from geoelectrical field curves. Geoelectrical sounding using the Schlumberger electrode array were conducted in the Njaba River sub-basin covering an area approximately 575km 2 . The Njaba River sub-basin is underlain by the Coastal Plain Sands (Benin Formation). The formation is made up of very friable sands with minor intercalations of clay. The data were interpreted to obtain the layer resistivities of the saturated and unsaturated zones. Porosity and degree of saturation and hence the specific yield were estimated from the electrical resistivity according to Archie's law. In spite of the uncertainties that exist in the relationship between resistivities and porosity and degree of saturation due to the generalized assumption on the material constants in Archie's law, the values of the specific yield obtained with the suggested geophysical method agree well with the values obtained from aquifer test in the study area. This study gives an insight into the groundwater potentials of the study area. Nigerian Journal of Technology and Education in Nigeria Vol. 8(1) 2003: 69-83

A geostatistical methodology to estimate the base of the Trifa aquifer (Morocco) with limited drilling and geo-electrical sounding data

The paper presents the methodology used to estimate the base and thickness of the Trifa aquifer, north-east Morocco, from very limited drilling and geoelectrical sounding data. The methodology is applicable where the aquifer is a single horizon with considerable lateral variation. The procedure is based on geostatistical techniques: kriging of apparent resistivities, calibration of the resistivities with information from drilling, co-kriging of resistivities and estimation of the thickness of the aquifer by inverting the apparent resistivity formula. Calculated and measured substratum levels are obtained by subtracting the estimated and measured thickness from the topography at the drilling and geo-electrical sounding locations. By co-kriging the estimated substratum levels with the measured values in the drilling locations, a map of the substratum over the plain was prepared.

Groundwater prospecting and management in an agro-based rural environment of crystalline terrain of India

An integrated hydrogeological investigation was made to delineate the socioeconomic problems in the agro-based rural environment of the crystalline terrain of Guntur district, Andhra Pradesh, India. The integrated investigation comprised geoelectrical (GE) surveys, remotely recorded data and pumping tests. The subsurface layer parameters obtained from the sounding interpretation are presented in the form of GE sections and a fence diagram. Characteristic resistivities of various layers were obtained by correlating the known lithology with the GE sounding data. Total transverse resistance (TTR) and total longitudinal conductance (TLC) were computed from the interpretation of the sounding data. The TTR map was compared with the depth of bedrock map and the values of TLC were correlated with the thickness of geoelectrical layers and water quality. Lineaments were mapped from the satellite imageries. Hydraulic properties were determined, using the standard pumping test analysis. Potentiality of aquifer zones was assessed, after comparing the known thickness of aquifer formations with the corresponding discharge (Q) values. The integrated study helps to evolve a criterion to classify the groundwater potential zones (GPZ) into low, medium and high, based on the thickness of the aquifer zone and its corresponding resistivity, TTR, TLC and Q. A management plan has been proposed for sustainable development of groundwater in the region to eliminate water scarcity and its related problems.

Aquifer parameter estimation from surface resistivity data.

This paper is devoted to the additional use, other than ground water exploration, of surface geoelectrical sounding data for aquifer hydraulic parameter estimation. In a mesoscopic framework, approximated analytical equations are developed separately for saline and for fresh water saturations. A few existing useful aquifer models, both for clean and shaley sandstones, are discussed in terms of their electrical and hydraulic effects, along with the linkage between the two. These equations are derived for insight and physical understanding of the phenomenon. In a macroscopic scale, a general aquifer model is proposed and analytical relations are derived for meaningful estimation, with a higher level of confidence, of hydraulic parameter from electrical parameters. The physical reasons for two different equations at the macroscopic level are explicitly explained to avoid confusion. Numerical examples from existing literature are reproduced to buttress our viewpoint.

Geoelectrical inversion for a one-dimensional anisotropic model and inherent non-uniqueness

Summary It has been shown that the inversion of geoelectrical sounding data from an anisotropic underground structure with an isotropic model can strongly distort the image of the resistivity distribution of the Earth. Because of this it is useful to extend the models to include an anisotropic earth. The inverse model used in this paper is a layered earth with general anisotropy, such that a 3 × 3 resistivity tensor is assigned to each layer. This symmetric, positive-definite resistivity tensor is parametrized by three principal resistivities and three Euler angles. Therefore, together with the thickness, seven parameters for each layer of the earth have to be resolved. The Marquardt–Levenberg method is used to invert the Schlumberger resistivity sounding data with an anisotropic model. The inversion results using synthetic data show that for an anisotropic earth, rather than all parameters, only particular parameter combinations can be resolved uniquely. Theoretical investigations support these conclusions and confirm that unlike the general non-uniqueness in geoelectrical inversion resulting from inaccurate, insufficient or inconsistent data, the non-uniqueness of geoelectrical inversion for an anisotropic model is an inherent one, which means that no unique solution can be obtained, even if perfect data are assumed.

Geoelectrical soundings and their relationship to hydraulic parameters in semiarid regions of Jalore, northwestern India

Geoelectrical soundings using the Schlumberger configuration were carried out in the close vicinity of twelve pumping test sites in the Jalore district of Rajasthan, India, to relate geoelectric and hydraulic parameters. Geoelectrical sounding data were interpreted by partial curve matching technique to obtain the initial model parameters. This initial starter model was then used to obtain the final layer parameters through inversion technique. From the inversion technique, the best-fitting, lower bound (minimum) and upper bound (maximum) models were derived under 1% error level. The best-fitted models were correlated with the litholog. The resistivities for most of the aquifer zones are found to be very low which may be due to deteriorating quality of groundwater besides their packing and grain size. The resistivities of collected water samples were determined to compute the formation factor and porosity. Computed formation factor and porosity were correlated with hydraulic conductivity. The formation factor is directly related to hydraulic conductivity whereas porosity is inversely related. The normalised aquifer resistivity was correlated with hydraulic conductivity and normalised transverse resistance with aquifer transmissivity. The hydraulic conductivity is found to be closely related with normalised resistivity and the transmissivity with normalised transverse resistance.

An effective ridge regression procedure for resistivity data inversion

The inversion of geoelectrical sounding data for the subsurface resistivity structure is a difficult task due to the nonlinear and nonunique nature of the problem. An effective algorithm for inverting resistivity data by ridge regression is described. It uses a line search procedure in a two-stage least-squares minimization process resulting in a stable and rapidly convergent algorithm. A FORTRAN-77 routine RIDGE based on the algorithm, its implementation and a driver program for magnetotelluric inversion MTINV, are discussed. The procedure is applied to magnetotelluric (MT) and transient electromagnetic (TEM) data to demonstrate its effectiveness and general applicability.

GEOELECTRICAL MODELS INVOLVING LAYERS WITH A LINEAR CHANGE IN RESISTIVITY AND THEIR USE IN THE INVESTIGATION OF CLAY DEPOSITS*

AbstractA model has been set up for the interpretation of geoelectrical sounding data for certain kinds of clay deposits containing gradually varying amounts of sand. The model assumes that in the so‐called gradient layer, resistivity varies linearly with depth. Model calculations show how such a layer can be replaced by two homogeneous layers.An inversion procedure using the Marquardt algorithm has been developed for the interpretation of sounding data obtained with the Schlumberger array; it assumes a gradient layer beneath several covering layers. The procedure is demonstrated on two clay deposits. A comparison is made between the newly developed interpretation, the traditional approach using model curves, and computerized inversion for a homogeneous layer model.

A GENERALIZED CAGNIARD GRAPH FOR THE INTERPRETATION OF GEOELECTRICAL SOUNDING DATA

AbstractThe Cagniard method of interpreting geoelectrical sounding data is based on the use of an empirical graph which expresses the relation between the resistivity and thickness of the second subsurface layer on one side, and on the other side the replacement resistivity and replacement thickness which are derived from the two‐layer sounding curve which is asymptotic to the second branch of the observed sounding curve. In his method separate graphs of this type are required for different values of the resistivity of the third subsurface layer. In the present paper a generalized Cagniard graph is derived which has the advantage of being independent of the value of the resistivity of the third subsurface layer. Finally, the accuracy of the method is discussed, and a procedure is described for extending its use to cases where more than three subsurface layers intervene.