Understanding the interrelationship between electrical anisotropy and groundwater yield in a typical Basement Complex area

Abstract

The rocks in the Basement Complexof southwestern Nigeria exhibit electrical anisotropy as a result of their heterogeneous nature caused by weathering, near-surface effects or presence of fractures. It is known that groundwater yield (Y) in a typical Basement Complex aquifers is related to its coefficient of anisotropy (λ). Therefore, it is essential to study the correlation between Y and λ in the basement complex. Ten (10) vertical electrical sounding (VES) points using Schlumberger array were studied in areas underlain by migmatite gneiss and quartzite rocks. The current electrode spacing (AB/2) varies from 1 m to a maximum spread length of 100 m. The quantitative interpretation of VES curves was done by using partial curve matching and computer assisted program called WinResist version 1.0 software. Dar Zarrouk parameters were estimated from the interpreted VES curves and thus coefficient of anisotropy (λ) was calculated from these parameters. Data on the groundwater yield at the VES points were also obtained. The results show that as λ increases, Y also increases with coefficient of correlation (R2) of 0.86 and 0.79 for migmatite gneiss and quartzite rocks respectively. To further investigate the relationship between Y andλ, a regression analysis was performed. The regression analysis that was performed on the dataset shows that λ contributes significantly to the regression models of the two rocks. The relationship between Y and λ reveals that groundwater yield could be predicted from the values of λ in a given locality.