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Report on visit to a WaterAid project, Nigeria, to carry out\ud workshops and assess geology of Benue State

By Alan MacDonald


This short report summarises activities and conclusions\ud from a visit to Nigeria by Alan MacDonald (6-21 January\ud 2001), other relevant information is attached. The terms of\ud reference for the visit were:\ud • to train WaterAid/WASU/BERWASSA staff to find\ud dolerite intrusions in Obi and Oju;\ud • to train staff in the use and interpretation of resistivity\ud equipment in Oju and Obi;\ud • carry out a desk study of the geological conditions of 7\ud LGAs in Benue State.\ud To meet these terms of reference a seven-day workshop\ud was undertaken in Oju/Obi comprising mainly fieldwork.\ud Three days were spent in Makurdi consulting geological\ud information available at the Geological Survey of Nigeria.\ud A summary of the main activities and recommendations\ud from the visit are given below.\ud 1. Boreholes drilled into dolerite intrusions offer the\ud cheapest and most sustainable water supply for much of\ud Obi. Therefore considerable time (1-2 days per community)\ud should be given to try to locate dolerite in communities\ud in Obi. The best method for finding it is to use EM34\ud and magnetics together and then validate using EM34 with\ud 40-m coil separations. WaterAid and WASU are competent\ud to carry out these activities.\ud 2. All workshop participants could competently use the\ud magnetic and EM34 equipment. Most could interpret the\ud data to identify areas with dolerite. However, for this year,\ud it is advisable for the WaterAid Engineer to validate interpretations\ud of any surveys.\ud 3. Resistivity is not a particularly useful technique in Oju\ud and Obi. Similar information is given by using EM34 at\ud 20-m spacings and then repeating with 40-m coil separation.\ud All participants recognised the pros and cons of using\ud resistivity and as a group we decided that we do not need to\ud continue using it in Oju and Obi. Most participants can\ud now roughly interpret resistivity data.\ud 4. The geological conditions of the 7 LGAs vary greatly.\ud The most difficult area for finding groundwater is probably\ud Gwer West. The geological conditions of all seven LGAs\ud are summarised in Table 3.\ud 5. The records from the 2000 drilling programme highlighted\ud several important issues.\ud • The boreholes were drilled and tested during the rainy\ud season when yields are artificially high.\ud • They were only grouted to a depth of one metre, therefore\ud leaving the laterite unsealed.\ud • The depth ranged from 22-51m (average 32.4 m) –\ud well short of the minimum depth of 40 m suggested by\ud BGS.\ud • The bailer tests were not carried out properly (and the\ud raw data not given) therefore it is impossible to assess\ud the yields of the boreholes.\ud 6. Several other issues arose during the visit, such as\ud the future use of the drilling rig; the distribution of reports\ud (both within the project and to other stakeholders). These\ud are discussed later in the report.\ud Summar

Publisher: British Geological Survey
Year: 2001
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