Sayoba Kafando's research while affiliated with Ministère de la Santé du Burkina Faso and other places

This characterization study of the aquifer horizons is based on the geostatistical analysis of the drilling data in order to map the intrinsic parameters of the aquifers, namely the size of the alterations and the size of the fissured fringe. The STRM data were also used to map the topographic levels. Cross-analysis of all these parameters with borehole flow rates allowed us to define a context pattern that is favorable to groundwater deposits, by identifying the influence of the size of these parameters on productivity. The application of the geophysical method (electric drag and geoelectric tomography) has made it possible to obtain a 2D vertical section of the subsoil structure based on the distribution of electrical resistivity. The alteration profile includes the alterite reservoir, the fissure reservoir located above the solid rock sometimes affected by fractures (fault). The size of these different horizons varies from one point to another, thus defining contexts that are more or less favorable for the existence of groundwater deposits. The alteration thickness (AT) mapping defined two map units: alteration thicknesses of 15m or less and those greater than 15m. Erosion would have played a large role in this distribution as there is a clear link between alteration thickness and topography. The alteration thickness (AT) unit of less than or equal to 15 m has great surface water potential. It is the area where the topography is fairly low, and the fractured edges are generally of considerable thickness. They frequently coincide with the large shallow areas drained by the major waterways.

The North-East of Burkina Faso is made up of formations of the Birimian basement rock. The region has a Sahelian climate where surface water resources are very limited. In order to assess the hydraulic potential of the existing aquifers, remote sensing and geophysical techniques (aeromagnetic and ground electric) were used. Satellite image processing and aeromagnetic survey data were used to generate a lineament map that was subsequently validated on the basis of existing geological, hydrogeological and topographical data, geomorphological field surveys and ground geophysical work. The resulting map displays a more or less dense network of 405 magnetic lineaments with a cumulative length of 1,787,676 meters as opposed to 94 lineaments from Landsat 8 images with a cumulative length of 970,054 meters. The average length of the magnetic lineaments is 4,414.01 meters while the average remote sensing length is 10,317.72 meters. The identified NE-SW and WNW-ESE fracture corridors are propitious for the presence of fracture aquifers. In addition to the lineament validation, the ground geophysics performed through electrical surveys allowed the characterization of the aquifers in the study area. Alteration thicknesses are generally less than 20 meters deep. The fractured horizon can reach 100 meters thickness under the alterites. The kernel density map highlights areas of good aquifer potential that could constitute significant groundwater reserves. Mapping aquifer potential is a crucial step in ensuring sustainable and efficient use of groundwater resources.

Topic 2.k. Hydrogeology and hydrogeologists from Sahelian countries: specific challenges for the achievement of SGD targets.

People in the semi-arid region of central Burkina Faso rely heavily on groundwater resources from basement rock aquifers for potable uses. In this study, the hydrogeochemical processes that control groundwater quality and contribute to better water resource management were characterised using major ion geochemistry, the calculation of water quality indices, and through the use of spatial geostatistical analysis. A total of 360 groundwater samples were collected in hand-pumped borewells. The overall low total dissolved solids of the groundwater indicates a fast recharge regime during the rainy season. Generally, the groundwater was circumneutral to alkaline in nature with dominant Ca2++Mg2+ and HCO3− concentrations. Based on the calculated water quality indices, most of the borewells sampled produced groundwater that was suitable for human consumption. However, a few borewells exhibited high As and F− concentrations that exceeded drinking water permissible limits. The high As concentrations were likely derived from weathering of volcano-sedimentary rocks, whereas, those of F− appeared to be from granitic rocks. Bivariate plots showed that geochemical processes such as silicate weathering, mineral dissolution and precipitation, ion exchange together with evapotranspiration were the primary factors influencing the groundwater solute acquisition. In addition, desorption and ion exchange under alkaline pH conditions could enhance As and F− enrichment in the groundwater. Spatial distribution maps of ionic strength and electrical conductivity identified the northern sector of the study area as the groundwater recharge areas, which should require protection and a periodic groundwater monitoring plan. The findings of this study may help decision-makers in setting up suitable groundwater quality management strategies and selecting locations for future borewell development in this semi-arid environment and fractured crystalline aquifers.

Les mesures in-situ de paramètres physico-chimiques, l’échantillonnage et l’analyse des ions majeurs des eaux de dix-sept (17) forages dans les environs de Kongoussi, province du Bam, Centre-Nord Burkina Faso, ont permis de mettre en évidence une distribution hétérogène des ions majeurs. Il ressort en termes d’abondance relative, l’ordre suivant des concentrations moyennes HCO 3 - > Ca 2+ > Na + > NO 3- > Mg 2+ > Cl - > K + . Concernant les faciès d’eau, c’est celui bicarbonaté calcique et magnésien (HCO 3 -Ca-Mg) qui domine. La principale origine de ces ions dans l’eau est l’altération des roches et le lessivage des sols. Toutefois, une origine anthropique s’aperçoit à travers les concentrations en NO 3 -, Cl - et K + des eaux de certains forages, sans pour autant être excessive pour Cl - et K + . La potabilité générale fait ressortir quelques forages avec des concentrations de NO 3- supérieures aux normes de 50 mg/l recommandés par l’Organisation Mondiale de la Santé (OMS). Les fortes concentrations de NO 3- entraînent l’apparition d’un faciès chloruré-nitraté. Les résultats montrent également qu’aucune eau ne présente de dureté supérieure à 300 mg/l (eau très dure), même si un peu plus de 41% se situent dans la frange eau dure.