Mapping the Hydraulic Potential of Fissured Aquifers in the Poni Watershed in South-West Burkina Faso

The Poni watershed, located in southwest Burkina Faso, is characterized by crystalline basement geological formations. The hydrogeology of the watershed is characterized by two types of aquifers: alterite aquifers and fissured aquifers. Fissured aquifers are still the most widely used for drinking water supply. The general objective of the present work is to map the hydraulic potential of fissured aquifers in the Poni watershed, in order to identify areas with high hydraulic potential for sustainable and rational management of groundwater resources. Four methodological approaches were developed, the first three of which resulted in thematic maps of fracture density, drainage density and alteration thickness, using Landsat 8 and airborne geophysical images, Digital Terrain Model (DTM) data and borehole data. Next, four flow classes were defined according to the minimum flow required for the various types of drinking water supply works in Burkina Faso, followed by a study of their distribution on the various thematic maps produced for the definition of the coastlines. Finally, a weighting was made on the basis of coasts and coefficients assigned to each parameter for mapping the hydraulic potential of fissured aquifers. Field data (boreholes, structural measurements and hydrogeological indices) and previous studies were used to validate the mapping. Analysis of the distribution of borehole flow rates on the various thematic maps shows that borehole productivity is optimal for a fracture density of between 1.55 and 1.9 km/km2, a drainage density of between 0.28 and 0.35 km/km2 and an alteration thickness of less than 25 m. Hydraulic potential was mapped using the weighting method, based on the distribution of borehole flow rates on maps of weathering thickness, drainage network density and fracturing density, highlighting three hydrogeological domains: the low-productivity zone, occupying 24.40% of the basin’s fissured aquifers, mainly found north of Gaoua, in the south-central and eastern parts of the basin around Gbomblora; the medium-productivity zone, occupying almost 31.57% of the fractured aquifers, is found mainly in the central-eastern part of the basin between Gaoua and Perigban, to the east of the commune of Gaoua, to the west of Kampti and to the west and north-east of Midebdo; and the good-productivity zone, representing 44, 04% of the basin’s fissured aquifers, it is located mainly in the north-western part of the basin, north of Loropéni, east of Kampti, around Perigban and in the south-east, notably north-east of Batié. The high-productivity zones almost overlap with all the Water Production Centers (CPE) identified within the watershed during a hydrogeological study commissioned by COWI in 2019 on the search for high-productivity zones on the crystalline basement. This study constitutes a guide which will guide groundwater research and must be carried out before any land use project.