Estimation of aquifer hydraulic parameters using geoelectric method in the Dukwi wellfields, northeastern Botswana

Abstract

A hydro-geophysical investigation was carried out in the northeastern parts of Botswana, in a wellfield called Dukwi, with the aim of estimating the aquifer hydraulic parameters employing the geo-electrical method. A Schlumberger electrode configuration of 16 vertical electrical soundings (VES) was carried out in the Dukwi Wellfield. The data were recorded with a maximum AB/2 spacing of 500 m and processed using the InterpexRESIXIP^tm software. In addition, physicochemical parameter measurements were carried out for 19 groundwater samples in the field. Aquifer hydraulic parameters, like hydraulic conductivity (K) and transmissivity (T), were computed from the pumping test data. An interpretation was made using statistics, including linear regression analysis. The major aquifer is the Mea Arkose Formation, and its estimated hydraulic conductivity and transmissivity ranges from 15.4 to 47.3 m/day and 539.9–2113.9 m²/day, respectively. The aquifer transverse resistance (Tr) and longitudinal conductance (S) of the rocks overlying the aquifer ranges from 945 to 2440 Ωm² and 1.5 to 9.7 Ω^-1, respectively. The R² value for the geo-electrical and pumping test K and T values are 0.689 and 0.896, respectively. The estimated K has a positive and strong correlation (R² = 0.946) with the resistivity. A strong positive correlation (R² = 0.892) is obtained between the estimated T and Tr of the aquifer. On the basis of these correlations, equations that relate the resistivity of the aquifer to its hydraulic parameters were formulated. These equations enable the evaluation of aquifer hydraulic parameters where there is a lack of pumping test data. Furthermore, these equations can be used in other parts of the country and in regions elsewhere that have similar geological and hydrogeological setups.