Abstract:
An integrated geophysical and hydrogeological approach has been used to investigate the
groundwater potential over the crystalline basement complex rocks of Ire – Akari Estate,
OritaObele, Akure, Southwestern Nigeria.This is with a view to characterise the study area into
groundwater potential zones. The continuous failure of pipe borne water supply and the
tremendous increase in population in the study area in the last ten years has stretched the available
water facilities to their limits. Based on this,the inhabitants of the study area depend mainly on
groundwater from hand dug wells and some functioning boreholes for their daily water needs
hence a growing demand for more groundwater.
The geophysical investigation involved the Very Low Frequency Electromagnetic (VLFEM)
and the Electrical Resistivity Methods using the Dipole-Dipole and the Vertical Electrical
Sounding (VES) techniques.The VLF-EM and the dipole-dipole profiles were conducted along the
established six traverses in an approximately east-west direction,ninety six (96) VES was
conducted while static water level measurements were carried out in sixty hand dug wells across
the study area.
Both the 2-D resistivity structure and the geoelectric sections revealed subsurface geologic
units consisting of the topsoil, laterite, weathered layer, fractured basement and the fresh basement
bedrock. Their resistivity values generally range from 12 – 372 ohm-m,39 – 617 ohm-m, 12 – 576
ohm-m, 51 – 714 ohm-m and305 – ∞ ohm-m respectively while the thickness values vary from
0.5 – 4.9 m, 1.8 – 17.6 m, 2.5 – 30 m, 4.8 – > 40 mrespectively. The depth to basement bedrock
range from5 – 37.8 m. The conductive zones delineated by the VLF-EM method, the weathered
layer and the fractured basement constitute the main aquifer units within the investigated area.The
static water level measurement for the peaks of dry and raining seasons generally varies from 1.3
– 9.9 m and 1.8 – 10.7 m respectively.
In conclusion, the groundwater potential map generated for the investigated area was used to
characterize the study area into low, medium and high groundwater potential zones.
