Borehole logging and slug tests for evaluating the applicability of electrical resistivity tomography for groundwater exploration in Nampula complex, Mozambique

Farisse Chirindja, Jan Erik Rosberg, Torleif Dahlin

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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 Wm). 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.

Original languageEnglish
Article number95
JournalWater
Volume9
Issue number2
DOIs
Publication statusPublished - 2017

Subject classification (UKÄ)

  • Water Engineering

Keywords

  • Borehole logging
  • Electrical Resistivity Tomography
  • Groundwater
  • Hard rock aquifer
  • Hydraulic conductivity
  • Slug test

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