Water in African soil

1Thirty percent of Africans do not have access to drinking water in sub-Saharan Africa, despite the construction of tens of thousands of wells and boreholes in recent decades. Forty percent of the boreholes drilled fail to discover water or, when they do, it is not enough to meet the demand. This raised the question of the approach used to determine the location of boreholes.

Groundwater exploration using magnetic resonance.

2In Africa, 40% of the subsoil consists of ancient, hard rocks. Deemed to be non-porous, they are assumed to let water flow when they are fractured. These areas are generally searched for on the surface using various techniques, including the analysis of aerial images or in situ soil resistivity measurements.

3In 2012, to assess this approach the GRIBA project was deployed in three countries where the subsoil consists of ancient rocks: Benin, Burkina Faso and Uganda. After analysing the results of many boreholes drilled over the past decades, and testing a number of new sites, it appeared that the main source of drinking water does not lie in fractures but in underground areas where rocks are altered and reduced to a sand-like state. This was a major breakthrough: groundwater should not only be sought in fracture zones.

Borehole equipped with a pump, Benin.

••• A new approach to help locate potable groundwater •••

4In 2015, researchers took it a step further by developing a method used to characterise these invisible, deep-seated sand alteration areas from the surface. It required two instruments: one standard tool used to measure electrical resistivity in two dimensions and detect sand alteration areas; and the other, RMP, developed by IRD and used to determine the volume of water available and estimate the potential withdrawal volume. This enabled the setting of sustainable abstraction thresholds, and Benin is acquiring the equipment needed to test this approach on a larger scale.

“This research, conducted in partnership with IRD, helped train junior and senior Benin researchers in the implementation of this new groundwater prospecting approach in bedrock areas. In addition, the population and the authorities are now aware of groundwater levels in the communities surveyed. At the end of the day, policy-makers have become aware of how effective this new approach is, and have incorporated it into tender specifications for drinking water supply in Benin.” 
Professor Nicaise Yalo, University of Abomey-Calavi, Benin