Estimation of Aquifer Hydraulic Characteristics from Surface Geoelectrical Methods: Case Study of the Rima Basin, North Western Nigeria

Abstract

Forty vertical electrical resistivity soundings (VES) were acquired, using a Schlumberger array. Three soundings were additionally made at existing boreholes in the vicinity of the study area for comparison. Since the area is a basement complex terrain, a maximum current electrode spacing of 200 m which is believed to probe down to the fresh basement in the area was used. This is believed to enable fresh basement in the area to be observed. The concept of Dar Zarrouk parameters (transverse unit resistance and longitudinal conductance in porous media) was used to determine aquifer hydraulic characteristics in the sedimentary formation underlying the area. The results of the interpreted VES data using a combination of curve matching technique and computer iterative modeling suggest that the area is underlain by between 3–5 geoelectric layers. The geologic sections derived from the equivalent geoelectrical sections revealed lithologic sequence of mostly five layers. However, there are minor isolated cases of three layers. The geoelectrical sections showed that the resistivity of the aquifer varies between 14.1 and 128.8 Ω m. The thickness of the aquifer ranges from 1.0 to 48 m while its depth from the surface lies between 1.0 and 50 m. Relationships between aquifer characteristics and the geoelectrical parameters revealed the hydraulic conductivity K and transmissivity T variations to be 3.10–28.34 m/day and 10.0–796.6 m2/day, respectively. The maximum K and T occur around VES 4 and 14; thus the maximum yield could be expected around VES 4 and 14.