Electrical Resistivity Tomography and Induced Polarization for Mapping the Subsurface of Alluvial Fans: A Case Study in Punata (Bolivia)

Abstract

Conceptual models of aquifer systems can be refined and complemented with geophysical data, and they can assist in understanding hydrogeological properties such as groundwater storage capacity. This research attempts to use geoelectrical methods, Electrical Resistivity Tomography and Induced Polarization parameters, for mapping the subsurface in alluvial fans and to demonstrate its applicability; the Punata alluvial fan was used as a case study. The resistivity measurements proved to be a good tool for mapping the subsurface in the fan, especially when used in combination with Induced Polarization parameters (i.e., Normalized Chargeability). The Punata alluvial fan characterization indicated that the top part of the subsurface is composed of boulders in a matrix of finer particles and that the grain size decreases with depth; the electrical resistivity of these deposits ranged from 200 to 1000 Ωm, while the values of normalized chargeability were lower than 0.05 mS/m. The bottom of the aquifer system consisted of a layer with high clay content, and the resistivity ranged from 10 to 100 Ωm, while the normalized chargeability is higher than 0.07 mS/m. With the integration of these results and lithological information, a refined conceptual model is proposed; this model gives a more detailed description of the local aquifer system. It can be concluded that geoelectrical methods are useful for mapping aquifer systems in alluvial fans.

Characterization of Aquifers in Metamorphic Rocks by Combined Use of Electrical Resistivity Tomography and Monitoring of Spring Hydrodynamics

“…Thus, a given rock type can have a large range of resistivity, from about 100 to 1 million Ωm, depending on whether it is saturated or dry. This characteristic is useful in the detection of fracture zones and other weathering features, such as in engineering and groundwater surveys [7][8][9][10]14,17,18].…”

“…More frequent but less productive springs are attributed to the draining of the shallow part of the alteration zone (mostly saprolite). Combination of the ERT method with spring monitoring proved to be very effective as a first and relatively inexpensive methodology for hydrogeological characterization of crystalline terrains, both in local and catchment scales.Geosciences 2020, 10, 137 2 of 18 complexity can be studied effectively by ERT to define aquifer geometry and geological structure and to gain insight into hydrogeological processes [6][7][8][9][10].Resistivity profiling gained renewed popularity during the 1990s with the introduction of computer-automated data collection systems and robust data inversion methods [11][12][13]. Recent advances in field instrumentation has led to the development of multi-channel, multi-electrode systems for quick and reliable data acquisition that greatly reduces human, computational, and time resources [2].…”

“…Geosciences 2020, 10, 137 2 of 18 complexity can be studied effectively by ERT to define aquifer geometry and geological structure and to gain insight into hydrogeological processes [6][7][8][9][10].…”

A Multidisciplinary Approach for Clarifying the Recharge Processes and Origin of Saline Water in the Semi-Arid Punata Alluvial fan in Bolivia

“…In order to confirm and assist in the interpretation of hypothesis (4), several geophysical campaigns were performed. The methods used were Electrical Resistivity Tomography (ERT) and Transient Electromagnetics (TEM), for more details about the surveys layout and results refer to Gonzales Amaya, Dahlin, Barmen, and Rosberg [15] and Gonzales Amaya, et al [45]. Figure 7 shows the electrical resistivity distribution and the corresponding hydrogeological interpretation from two different areas in the Punata fan: area 1 (A-1) and area 2 (A-2), refer to Figure 1a for location.…”

“…(a) Study area and location of water samples. The water samples are classified in surface water and groundwater; (b) Cross section of the Punata alluvial fan, where the question mark means that the depth to bedrock is still unknown, from Gonzales Amaya, et al[15].…”