HYDROCHEMICAL CHARACTERIZATION OF THE SUPERFICIAL AQUIFER OF DOBA, SOUTHERN CHAD
Keywords:
Hydrochemistry, Aquifer, groundwater, Mineralization, DobaAbstract
Water is a very important resource and ensures the survival of man on a global scale. In the south of Chad, more precisely in (Doba), this resource is buried in vast areas made up of sedimentary formations (sands, sandstones). The latter host Cretaceous and Continental Terminal aquifers whose knowledge of chemical and piezometric properties is limited. The objective of this work aims to know the water level, characterize the nature of groundwater from the chemical elements and by determining the relationships between the ions and the origin of the mineralization of the groundwater. A total of 31 in situ measurements (temperature, Ph, TDS, salinity, conductivity), 38 piezometric measurements and 25 water samples are taken during field campaigns during low water periods. After investigations, it appears that the piezometric heights vary from 359 to 423.88 m. The highest point is in the South-West at Békondjo 2 (P13) and the depressions in the center at Ndounambo (F4), a little to the East at Dogouti 1 (F1) and at Bedogo in the North-West (P20). Temperatures range from 21.2 (well P5 at Bo bouete) to 33.3°C (well F1 at Dogouti). All the water sampled has pH values between 7.11 (Békondjo F6 borehole) and 8.89 (Ndounambo P8 well), thus indicating a basic character. The waters have conductivities between 17.9 (well P15 at Mismadji) and 368 µs.cm-1 (well P21 at Divers). TDS values range from 13.1 to 261 mg/l. The distribution of the waters analyzed in the piper diagram shows two categories of water (groundwater, surface) divided into three facies: Sodic and potassium carbonate Na-K-(CO3), calcium bicarbonate and magnesium Ca-Mg-(HCO3 + CO3) facies as well as the sodium and potassium chloride facies. The waters have an average nitrate concentration (between 3 and 19 mg/l). Geochemical modeling shows that the waters are mostly supersaturated with respect to dolomite, balanced majority and undersaturated with respect to aragonite and calcite. The carbonated and bicarbonated waters composed mainly of calcite, dolomite, show that the origin of the mineralization of the waters of two layers would be linked to the lithological nature and by the dissolution of the minerals. Geochemical modeling shows that the waters are mostly supersaturated with respect to dolomite, balanced majority and undersaturated with respect to aragonite and calcite. The carbonated and bicarbonated waters composed mainly of calcite, dolomite, show that the origin of the mineralization of the waters of two layers would be linked to the lithological nature and by the dissolution of the minerals. Geochemical modeling shows that the waters are mostly supersaturated with respect to dolomite, balanced majority and undersaturated with respect to aragonite and calcite. The carbonated and bicarbonated waters composed mainly of calcite, dolomite, show that the origin of the mineralization of the waters of two layers would be linked to the lithological nature and by the dissolution of the minerals.