Geohydrological Reconnaissance in Upper Volta

The landlocked Republic or Upper Voira lies in the heart of West Africa and comprises a wide lareritic plateau at the south edge of the Sahara Desert. From south to north, the rainfall decreases from about 1.200 mm. to less than 500 mm.; the evaporation increases from a low of 1,945 mm. to 3,385 mm.; and temperatures from 30° C to 34° C. Latentic rocks occur as surficial deposits over much of the reconnaissance area, and generally are ferruginous, hard, and cemented. The underlying bedrock consists primarily of granite and granodiorite with lesser amounts of metamorphics. The so‐called “under latérite” materials, consisting of the weathering products of the igneous and metamorphic rocks, constitute the principal aquifers in the investigated areas. These clays and sands generally can be counted upon to yield small supplies of water, adequate for at least domestic and stock use. Large‐diameter dug wells are used exclusively to tap the thin water‐bearing zones. Where 15 meters or more of weathered material occur above fresh bedrock, water can be found and exploited. A “good” well is one which produces 2,000 liters b per hour. The chief importance of the bedrock as a source of water is that it may yield at least a small quantity of water from fractures at most localities where ir is below the water table. Water in sufficient quantity and adequate quality is not now available to raise the standards of living in the 631 villages in the areas visited. Most of the immediate need can be met by developing ground water from the weathered material through large‐diameter dug wells.