Groundwater Exploration With Aem in the Boteti Area, Botswana

Daniel Sattel; Lesego Kgotlhang

doi:10.1071/EG04147

ISSN: 0812-3985
E-ISSN: 1834-7533

Groundwater Exploration With Aem in the Boteti Area, Botswana
Authors Daniel Sattel and Lesego Kgotlhang
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 35, Issue 2, Jun 2004, p. 147 - 156
DOI: https://doi.org/10.1071/EG04147
- Received: 03 Mar 2004
- Accepted: 01 Feb 2003
- Published online: 01 Jun 2004

Abstract

AEM data acquired with the TEMPEST system in the Boteti area, Botswana, were used to map lithologies and structures for potential fresh groundwater. The survey area is characterised by the Makgadikgadi paleolake system bordered by elevated terrain to the south. Lower-lying areas are characterised by a thick layer of Kalahari Beds with saline groundwater generally situated less than 20 m below surface. Elevated areas are generally characterised by Karoo sediments, consisting of sandstones and mudstones, at shallow depths.

Within the paleolacustrine terrain, target aquifers are freshwater zones associated with recharge pans above a saline water table. The correlation of AEM-derived conductivity-depth profiles with borehole records shows that the conductivity of Kalahari Beds is primarily a function of clay content, water saturation, and water salinity. The shallow conductivity structure from modelled AEM data outlines several resistive zones, some of them located within Boteti River alluvium beneath the present and past river channels.

In the elevated terrain, target aquifers are sandstones lying between dry alluvium or basalt, and mudstone. Basalts are characterised by very low conductivities and a strong magnetic response. The underlying sandstones and mudstones have low and high conductivities, respectively, and are offset by horst and graben structures, which are mapped in both the magnetic data and conductivity-depth sections. Resistivity iso-surfaces generated from the 3D conductivity data facilitate the spatial appreciation of the geometry of modelled structures. Favourable locations for freshwater exploitation interpreted from TEMPEST data include faults, dykes, a paleochannel incised into mudstone, and shallow fractured sandstone especially when overlain by basalt.

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References

Cooke, HJ. and Verstappen, H., 1994, The landforms of the western Makgadikgadi Basin of northern Botswana, with a consideration of the chronology of Lake Palaeo-Makgadikgadi: Zeitschrift fiir Geomorphologie NF, 28, 1-19.
Hydrogeo Pty Ltd and Water Surveys (Botswana), 2001, Groundwater resources investigation in the Boteti Area, inception report, groundwater resources, vol. 2: Department of Water Affairs, Botswana.
Lane, R., Green, A., Golding, C, Owers, M., Pik, P., Plunkett, C, Sattel, D., and Thorn, B., 2000, An example of 3D conductivity mapping using the TEMPEST AEM system: Exploration Geophysics, 31, 162-172.
Lane, R. and Pracilio, G., 2000, Visualisation of sub-surface conductivity derived from airborne EM: Ann. Symp. Environ. Eng. Geophys. Soc. (SAGEEP 2000) Expanded Abstracts, 101-111.
Lane, R., Heislers, D., and McDonald, P., 2001, Filling the gaps - validation and integration of airborne EM data with surface and subsurface observations for catchment management - an example from Bendigo, Victoria, Australia: Exploration Geophysics, 32, 225-235.
Macnae, L, King, A., Stolz, N., Osmakoff, A. and Blaha, A., 1998, Fast AEM data processing and inversion: Exploration Geophysics, 29, 163-169.
Sattel, D., 1998, Conductivity information in three dimensions: Exploration Geophysics, 29, 157-162.
Sattel, D., 2002, Modelling AEM data with Zohdy’s method: 72nd Annual International Meeting, Society of Exploration Geophysicists, Expanded Abstracts, session ACQ1.8, 30-33.
Sattel, D., 2003, The resolution of shallow horizontal structure with AEM: 16th ASEG Geophysical Conference and Exhibition, Extended Abstracts.
Sattel, D. and Kgotlhang, L., 2003a, Modelling aquifer structures with AEM in the Boteti Area, Botswana: Ann. Symp. Environ. Eng. Geophys. Soc. (SAGEEP 2003), Expanded Abstracts, 36-4.
Sattel, D. and Kgotlhang, L., 2003b, Groundwater exploration with AEM in the Boteti Area, Botswana: 16th ASEG Geophysical Conference and Exhibition, Extended Abstracts.
Smith, R.A., 1984, The lithostratigraphy of the Karoo Supergroup in Botswana: Geological Survey of Botswana, Bulletin 26, 239 pp.
Thomas, D.S.G. and Shaw, PA., 1991, The Kalahari environment: Cambridge University Press, 284 pp.

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Article Type: Research Article

Keyword(s): Airborne electromagnetics; EM modelling; groundwater exploration; TEMPEST

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Groundwater Exploration With Aem in the Boteti Area, Botswana

Abstract

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