Abstract
In Nampula province, Mozambique, there is a high number of water wells considered as having failed for having too low a pumping yield. Two Electrical Resistivity Tomography (ERT) measurement campaigns were conducted in the area for evaluating the reasons of failures. However, in some cases it was difficult to verify and interpret the ERT results by only using the inadequate lithological description presented in drilling reports. In this paper the integration of borehole logging and slug testing is presented as a solution to add more information and to enhance the interpretation of ERT models. The borehole logging tool measured resistivity, magnetic susceptibility and natural gamma. The logging results proved that the ERT models are accurate in estimating the resistivity for basement (>1400 Ωm), fractured layer (220–1400 Ωm), semi-weathered layer with clay accumulation (10–220 Ωm), and weathered and leached layer (220–2700 Ωm). The slug testing gave results of high hydraulic conductivity (K) values where the ERT indicates well-developed weathered and fractured layers, and low K values where these are less developed. The borehole interpretation can be extrapolated using the ERT model to give a geometric characterization of the aquifer. Therefore, the implementation of the ERT method in groundwater exploration is encouraged.
Highlights
Geophysical methods have made a valuable contribution to identification of groundwater resources in basement aquifers [1,2]
The surveyed surveyedboreholes boreholes all located in Nampula province
The inverted Electrical Resistivity Tomography (ERT) models were classified in three different layers based on the information of Acworth weathering profile
Summary
Geophysical methods have made a valuable contribution to identification of groundwater resources in basement aquifers [1,2]. As the geology is complex, the interpretation of geophysical data is always problematic It needs additional information from aerial photography, geological and tectonic maps and core description to reduce uncertainties. When such information is not available, a combination of different geophysical methods can improve the interpretation. There is a report with information about the drilling rate, geological logging, borehole and groundwater depth, dynamic and static level, and pumping test and water quality results. The accuracy of these reports is questionable due to inconsistency of the information. It was reported as a failure rate of about
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