ELECTRICAL RESISTIVITY SURVEY FOR GROUND WATER POTENTIALS IN SHAKWATU, NIGER STATE, NIGERIA.

Abstract

ABSTRACT The Schlumberger configuration of the geophysical electrical resistivity method was employed to investigate the groundwater potential in Shakwatu, Niger State, part of the topographical Minna Sheet 164. Geologically the area is considered as part of the crystalline basement complex characterized with rocks such as migmatite-gneiss, granite, quartzite and schist. A total of 36 VES points were established along six profile lines employing the SAS 4000 Terameter. The interval between the profile lines and the intervals between the VES points was set at 100 m respectively. The maximum current electrode spacing (AB/2) was set at 100 m while the maximum potential electrode separation (MN/2) was set at 15m. The geoelectric data were plotted with the aid of the Win resist inversion software. Geoelectric parameter obtained from the iterated model geoelectric curves were interpreted through qualitative and quantitative methods such as geoelectric sections, iso-resistivity maps and iso-patch maps. Three curve types were noticed from the model geologic curve. These include the HA (ℓ1 > ℓ2 < ℓ3), A (ℓ1< ℓ2 < ℓ3) and AK curve types. All the geoelectric sections of the six profiles are composed of three geoelectric layers. The apparent resistivity of the first and second geoelectric layer ranges from 18 Ωm to 695 Ωm and 11 Ωm to 1782 Ωm respectively with a thickness range of 0.5 m to 1.6 m and 1.1 m to 16.4 m for the first and second layers. The depth to the first layer ranges from 0.5 m to 1.6 m and 1.9 m to 17.5 m for the second geoelectric layers. The third geoelectric layer shows a resistivity range of 493 Ωm to 5631 Ωm which extends to an infinite depth. The first layer iso-resistivity map indicates low to moderate resistivity with the lowest resistivity indicated within the southern, central and north-western portion of the mapped area. The iso-resistivity map of the second geoelectric layer indicates low resistivity values across the layer. The north-eastern, south-eastern and south-western portions of the area displayed the lowest resistive zones; the northern portion is the resistive portion of this layer. The isoresistivity map of the third geoelectric layer indicates moderate to high resistivity values. The potential VES points for groundwater exploitation in the study area includes P1V3 which indicates low to moderate resistivity at greater depth. VES points P6V1 and P2V2 which indicate a fairly thick overburden material are also considered as potential points for groundwater exploitation.