Groundwater prospecting in Southern Sekyere West District using electromagnetic method
Loading...
Date
2000-02-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The Electromagnet (EM) method has been employed in the investigation of the groundwater potential in some communities within the Southern Sekyere West District.
The field technique involved the use of electromagnetic profiling in mapping the subsurface conductivities at two different depths, based on the principle of Electromagnetism. The equipment used is the Geonics EM34-3 equipment and was operated in the horizontal dipole (H.D) and vertical dipole (V.D) modes at a 20 m intercoil spacing and probing depths of 15 and 30 m respectively. The nature of the conductivities at these two depths for each profile in the communities was determined and potential zones of groundwater accumulation identified after a preliminary interpretation.
In general, a target conductivity range of 12 to 24 mS/m for sandstone areas and 28 to 65 mS/m for shally areas was expected for groundwater occurrence, based on previous results.
In addition to the qualitative interpretation of the profiling results, vertical cross sections, which effectively show potential zones of groundwater accumulation, have been prepared for some selected drill sites and the results compared with those from drilling.
The following results were obtained for some of the selected communities. At Asubuaso, the expected depth of striking groundwater, as deduced from the vertical cross-section was 17 m, while drilling yielded water at 18. m; at Kwabena Akura the expected depth was 20 m while the actual drilling records indicated water at 21 m; at Konab Akura the expected depth of striking water was 22 m while from the results of drilling, water was obtained at 44 m depth. However, between the depth of 22 and 44 m, the ground was very moist; at Denkyirakrom, groundwater was expected at 15 m, while the drilling indicated water at 16 m. At other places, the groundwater was deduced to be present but the drilling yielded dry holes. Other points which were not considered to be within the target conductivity range also yielded water during test drilling.
These results indicate that the electromagnetic (EM) technique can be used to effectively locate and map water bearing zones in subsurface rocks. However, due to ambiguities in the interpretation of the field results, it is necessary to backup this technique with geoelectrical sounding or other EM methods in order to optimise the conductivity profiling results for a cost effective borehole sitting programme.
Description
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of Master of Science in Geophysics, 2000