True 2-D Resistivity Imaging from Vertical Electrical Soundings to Support More Sustainable Rural Water Supply Borehole Siting in Malawi
Abstract
:Featured Application
Abstract
1. Introduction
2. Materials and Methods
2.1. Study Setting
2.1.1. Geological and Hydrogeological Setting
2.2. Survey Methodology: Rationale and Approach
2.3. Geophysical Survey Methods
2.3.1. Survey Configuration and Equipment Preparation
2.3.2. Measurement Acquisition
2.3.3. Survey Site Selection and Survey Preparation
2.3.4. Survey Acquisition
2.3.5. Survey Processing
- Main input file R2.in, containing, inter alia, a definition of the quadrilateral mesh, a list of the electrodes with their positions, a surface-elevation profile to account for the topography; a definition of parameter blocks (i.e., zones of same inverted resistivity over neighbouring cells) and settings of inversion parameters (to calculate a sensitivity matrix);
- File protocol.dat listing all resistances recorded in the survey and their respective pairs of current electrodes and potential electrodes.
2.3.6. Survey Interpretation
2.4. Evaluation of Aquifer Potential
2.5. Demonstration of Site Application
3. Results
3.1. Malaza Survey
3.1.1. Site and Survey Layout
3.1.2. Cross-Section
3.1.3. Aquifer Potential
3.2. Msako Survey
3.2.1. Site and Survey Layout
3.2.2. Cross-Section
3.2.3. Aquifer Potential
3.3. Dete Survey
3.3.1. Site and Survey Layout
3.3.2. Cross-Section
3.3.3. Aquifer Potential
3.4. Muzongo Survey
3.4.1. Site and Survey Layout
3.4.2. Cross-Section
3.4.3. Outcrop Analysis
3.4.4. Aquifer Potential
4. Discussion
4.1. Method Performance
4.1.1. Imaging Performance
4.1.2. Operational Performance
4.2. Potential for Technology Deployment
4.2.1. Applications
- Integration with drilling: The most important application in Malawi would be assisting improved siting of supply boreholes. It may also help identify lithologies, faults and fractures, and thereby would help anticipate the mechanical behaviour of formations to be drilled and aid optimal selection of drilling methods.
- Integration with other surface geophysics: Combined deployment with MP may be beneficial, as, although only qualitative answers are provided by MP about the subsurface configuration, it may still enable the identification of lineaments or help distinguish lithologies with different magnetic signatures that may appear similar on resistivity cross-sections. There is no benefit associated with combining the resistivity method implemented with conventional VES or EMP used in Malawi.
- Integration with borehole logging: Borehole-scale geological calibration and validation of the geophysical survey section (not possible in the current study due to a lack of nearby logged boreholes) will increase confidence in its geological interpretation and predictive use. Geomechanical parameters of drilled formations (hardness, stiffness, abrasivity, etc.) may be compared to resistivity cross-sections, to check for any correlations. Drill-cutting analyses and borehole CCTV image may help identify geological features too small or of insufficient contrast to be identified by resistivity. They may help identify unexplained features observed on resistivity cross-sections and whether transitions are real or artefacts of inversion smoothing. Conversely, large-scale features on cross-sections may help interpret much smaller-scale drill cutting or CCTV image observations.
- Integration with aquifer testing: Aquifer shape and dimensions, presence and continuity of confining units and aquifer boundaries, and aquifer heterogeneity and zonation are critical parameters to inform the analysis of aquifer pumping test data and may all be determined on the resistivity cross-sections. Likewise, pumping test and borehole rest water-level measurements permit more quantitative hydrogeological conceptualisation of the resistivity section.
4.2.2. Hardware and Software Requirements
4.2.3. Capacity Building
5. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Leborgne, R.; Rivett, M.O.; Wanangwa, G.J.; Sentenac, P.; Kalin, R.M. True 2-D Resistivity Imaging from Vertical Electrical Soundings to Support More Sustainable Rural Water Supply Borehole Siting in Malawi. Appl. Sci. 2021, 11, 1162. https://doi.org/10.3390/app11031162
Leborgne R, Rivett MO, Wanangwa GJ, Sentenac P, Kalin RM. True 2-D Resistivity Imaging from Vertical Electrical Soundings to Support More Sustainable Rural Water Supply Borehole Siting in Malawi. Applied Sciences. 2021; 11(3):1162. https://doi.org/10.3390/app11031162
Chicago/Turabian StyleLeborgne, Romain, Michael O. Rivett, Gift J. Wanangwa, Philippe Sentenac, and Robert M. Kalin. 2021. "True 2-D Resistivity Imaging from Vertical Electrical Soundings to Support More Sustainable Rural Water Supply Borehole Siting in Malawi" Applied Sciences 11, no. 3: 1162. https://doi.org/10.3390/app11031162
APA StyleLeborgne, R., Rivett, M. O., Wanangwa, G. J., Sentenac, P., & Kalin, R. M. (2021). True 2-D Resistivity Imaging from Vertical Electrical Soundings to Support More Sustainable Rural Water Supply Borehole Siting in Malawi. Applied Sciences, 11(3), 1162. https://doi.org/10.3390/app11031162