Integrated geophysical approach in groundwater exploration of WallaB, Gwoza local government area of Borno state, Nigeria.
A combined geophysical investigation comprising electromagnetic (EM) and resistivity depth sounding carried out around Gwoza area indicate that the area is suitable for borehole development. The electromagnetic results along six profiles identified five locations that are favorable for detail vertical electrical sounding investigations. These locations with a conductivity range of 28-77 Sm-1 were further studied with the help of the Schlumberger electrode array. Both manual and computer interpretations of the resistivity survey indicate three geo-electric horizons in the study area. The first horizon is interpreted to be the overburden, a sandy clay horizon with thickness and resistivity values in the range of 0.90 – 1.50 m and 103.3– 320.7ohm-m respectively. Weathered granite consisting dominantly of clayey material is the second geo-electric unit. This unit has a thickness range of 7.20 –14.42m and resistivity of 12.0–20.7ohm-m. The most important hydrogeological horizon in the study area is the third horizon demonstrated by fractured granites. This is also the geo-electric basement for the maximum current electrode separation attained during the survey. Its resistivity is between 342.6 – 652 Ohm-m. As a result of the thickness of, and the low clay content of the third geo electric horizon, the authors recommend all the VES stations for future borehole location in the area.
Keywords: Electromagnetic Survey, Resistivity technique, Groundwater, Basement Complex.