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Kwame Nkrumah University of Science and Technology (2009)

Geophysical investigation for groundwater in the Gushiegu-Karaga and Zabzugu-tatale Districts of the Northern Region of Ghana using the electromagnetic method

Tsikudo, Blessing Kwasi

Titre : Geophysical investigation for groundwater in the Gushiegu-Karaga and Zabzugu-tatale Districts of the Northern Region of Ghana using the electromagnetic method.

Auteur : Tsikudo, Blessing Kwasi

Université de soutenance : Kwame Nkrumah University of Science and Technology

Grade : Master of Science , 2009.

Résumé
Due to the lack of access to potable drinking water in the Gushiegu-Karaga and Zabzugu Tatale Districts of the Northern Region of Ghana, Geophysical investigation has been carried out with the aim of mapping out potential groundwater sites for boreholes to be drilled for these communities. Electromagnetic profiling using the Geonics EM-34 conductivity meter was carried out in 15 communities ; seven in the Gushiegu-Karaga and eight in the Zabzugu-Tatale District. The EM equipment was operated in the horizontal (HD) and vertical dipole (V.D) modes with a 20 m intercoil spacing, probing depths of 15 and 30 m respectively. Analysis and interpretation of the field results in the two districts revealed that potential aquifers within the various communities could be located with respect to two distinct features namely, weathered and fractured zones. Three lithologic logs for each District obtained for the points recommended have been presented and compared with profiling results in order to provide a scientific basis for siting of similar boreholes in virgin areas. The results also show a response, which is significantly different from that of the weathered and fractured zones. It indicates a nearly symmetrical negative response, with values as low as 5 mS/m in some communities. This was interpreted to be due to dike-like structures or a highly conductive material that has been masked, which could contain water. The lithologic logs of the communities in the Gushiegu-Karaga District revealed that the topmost part consists of brown loose laterite with the subsurface underlain with hard fresh fractured siltstone with at times, sandstone intercalations. The yield of the boreholes drilled within these communities was between 21 and 73 litres/min and the aquifer horizon averagely between 30-60 m. On the other hand, the logs of the communities in Zabzugu-Tatale District revealed that the topmost layer consists of brown sandy laterite with the subsurface underlain with grey hard quartzite with at times, siltstone intercalations. The yield of the boreholes drilled within these communities were between 10 and 117 litres/min and the aquifer horizon averagely between 30 and 70 m. The result of the study yielded a 75% success rate which confirms that the Electromagnetic Method is very suitable for sitting boreholes in these communities. To increase this success rate, it is recommended that the combination of two or more geophysical techniques such the Vertical Electrical Sounding and other EM methods be considered in the future to ensure a more accurate selection of potential drilling sites.

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