Estimation of Aquifer Hydraulic Parameters Using Geo-electric Method in the Dukwi Wellfields, North-eastern Botswana

Abstract

Abstract Aquifer hydraulic parameters were estimated using geo-electric methods in the Dukwi wellfields, northeastern Botswana. 16 vertical electrical sounding (VES) were recorded using the Schlumberger electrode configuration with maximum half current electrode spacing of 500 m. The data were inverted using the Interpex RESIXIPtm software. In-situ measurements of physico-chemical parameters were conducted in 19 groundwater samples. Pumping test data were also analyzed to determine aquifer hydraulic parameters. Statistical and linear regression models were used for the interpretation of the data. The main aquifer is the Mea Arkose formation, and its average estimated hydraulic conductivity and transmissivity is 31.60 m/day and 1442 m2/day, respectively. The mean transverse resistance and longitudinal conductance of the aquifer and the rock overlying the aquifer, respectively, is 1932 Ωm2 and 4.57 Ω-1. The R2 value for the geo-electrical and pumping test hydraulic conductivity and transmissivity values is 0.6871 and 0.8896, respectively. The estimated hydraulic conductivity has a positive and good correlation (R2 = 0.6606) with the resistivity and a strong correlation coefficient (R2 = 0.8948) is obtained between the transmissivity of the aquifer and the Transverse resistance. Based on the correlations, equations that relate the resistivity of the aquifer to the hydraulic parameters such as transmissivity and hydraulic conductivity were formulated. These equations enable the determination of the aquifer hydraulic parameters where there is a paucity of pumping test data. Furthermore, these equations can be used in other parts of the country, and elsewhere, that have similar geological sequences and hydrogeological setup.