Interpretation of results (left) and explanation about TDEM (right)

The first field experiment as part of the ISGEAG project was recently completed with big success. The geophysical field experiment was executed in Kajiado Town, Kenya, between 18th and 28th of April, 2017, with participants from KenGen, AMREF Kenya, University of Nairobi, the Kenya Water Institute (KEWI) and the Masai Technical Training Institute (MTTI). The area is characterized by a complex basement geology where a combination of new and traditional geophysical techniques where integrated in order to get a better understanding of the hydrogeology for sustainable drinking and irrigation water for the benefit of the population in the relatively rapidly growing capital of Kajiado County.

The project partners – Acacia Water, SamSam Water, KenGen and AMREF Kenya – performed both traditional and new geophysical techniques, including Time Domain Electro-Magnetics (TDEM) and Audio Magneto Telluric (AMT), and combined and compared the results, in order to test the applicability of the methods and to come to a new hydrogeological concept in which we were able to identify a promising local fractured aquifer near the Kajiado River, which runs from North to South along the western side of Kajiado Town.

In linkage to the VIA Water Kajiado Sponge City project, the project partners were able to ascertain a relative simple concept for intervention: combining recharge from excess of city rain and run-off water with riverbank infiltration that would artificially recharge this aquifer and therefore could form the basis of a sustainable future water supply for Kajiado town.

The mission was also perceived very educative and innovative for all participants, which included geologists, geophysicists, operators of geophysical equipment, students and trainees from various organizations and institutes. The main insights obtained included:
• The added value of Electrical Resistance Tomography (ERT) compared to the conventional horizontal electrical profiling (HEP) and vertical electrical soundings (VES);
• Better understanding of different possibilities as well as sometimes limited and misleading interpretation of HEP and VESes;
• Added value of using different electrode configurations with ERT;
• To be able to discuss and substantiate geophysical interpretations and to build a hydrogeological concept based on the measurement results;
• The impact and wide-range of possibilities on recharge and sustainability of this concept, with close linkages to the VIA Water Kajiado Sponge City project;
• The use and potential of TDEM/AMT in metamorphic basement, with increasing resistivity and vertical conductors (faults) compared to ERT;
• Resolution and exploration depth of TDEM compared to ERT.

At this very moment we are still analysing the excellent data series provided by the different geophysical methods used. Nevertheless, the top figure shows a first concept of interpretation of the geophysical measurement results.