Dear ISGEAG-project owners,
We hope that the implementation of your project goes well.
As NOEVA (HydroGeophysics in Coastal zone of Benin) project owner which is funded by Via-Water program, we would like to inform you that our web page has just been created on the Via water website (https://www.viawater.nl/projects/noeva-hydrogeophysics-in-coastal-zone-o...).
Our main goal is to develop a new approach based on geophysical method (TDEM, ERT and MRS) by which groundwater resources of African coastal cities can be better known and then sustainably used.
Recently, our team was working on a project named GRIBA (Groundwater Resources In Basement rocks of Africa) aiming at improving the geophysical implementation for borehole siting in hard rocks area and funded by the African and European Union. Through this project, we gained a lot of experience and knowledge that we will be happy to share with you.
We wrote an article about borehole siting in hard rocks context using direct current geophysics. In this paper we presented a figure (Fig1) showing that the electrical profiling anomalies selected as targets result from clayey areas within the saprolitic layer (Fig1-a). Borehole F1 (Fig1-c) was drilled on one of these anomalies for which interpretation of electrical sounding is at right (Fig1-b) and was negative (i.e. yielded less than the threshold of 0.7 m3/h). Based on the ERT interpretation, a less clayey area was selected to drill the second borehole F2 in the surroundings. The borehole F2 has a higher and acceptable yield of 1 m3/h and is therefore positive.
Fig. 1. EP, VES and ERT results on mica shist area. a) EP with Schlumberger and Wenner arrays; b) VES on anomaly N°1 on Schlumberger EP; c) ERT section using WA and WB arrays.
Finally we conclude that:
- Electrical profiling frequently misleads practitioners by siting boreholes in clayey zones
- Electrical soundings are often affected by 2D effects and their interpretations are carried out with a 1D hypothesis
- As compared to 1D techniques, ERT results in a better resolution of both 2D geological structures and characterization of the main hydrogeological targets which are the saprolitic and the stratiform fractured layers.
Did your research works carried out in Kenya lead you to similar conclusions?
The paper is actually in press and we will send it to you once it would have been published to start discussions together on geophysical implementation for borehole siting in hard rock area.
Please do not hesitate to let us know if you know or hear about similar projects with which it would be interesting to discuss.