This study is aimed at evaluating groundwater potential of Ipinsa-Okeodu area, near Akure, Southwestern Nigeria. A multi-criteria model was developed for achieving this aim; the GRT model which is based on geology of each sounding point, resistivity, and thickness of the aquifer across the study area was successfully used to evaluate the aquifer potential of the area for future groundwater development programme in the area. Geophysical investigation involving vertical electrical sounding was carried out across the study area. A total of one hundred and two (102) vertical electrical soundings (VES) data were acquired using Schlumberger array with maximum half-current electrode separation of 150 m. Three to five geoelectric layers were delineated across the study area. The predominant curve types are KH, H, K and A. The maps of aquifer layer resistivity and aquifer layer thickness were generated and synthesized with the geology of the study area in producing the GRT model map/groundwater potential map. The groundwater potential map shows that the area is characterized by five groundwater potential zones; poor, low, moderate, good and high. The northwestern regions, north central and part of the southwestern regions are high groundwater potential zones, the northern and most part of southeastern zone are of moderate potential, while small portion in the southeastern and northern zones are of low groundwater potential.

ABSTRACT:Integrated surface geophysical methods were used in investigating causes of pavement instability along a portion of Akure-Owo expressway, southwestern, Nigeria. The methods comprise of ground magnetic profiling, Very Low Frequency Electromagnetic (VLF-EM) profiling and geoelectric sounding. The magnetic profile shows a drop below 31500nT at distance 100m and above 32500nT at distances 140 and 310m, these drops in value could correspond to lithological contacts or bedrock depressions. The combined plots of raw real and filtered real VLF-EM data show conductive zones at distances 70m, 230-240m and 350-360m, which could be indicative of fractured zones or conductive clay materials. The 2-D geoelectric section shows bedrock depressions at distance 80-160m (stable segment) and 240-360m (unstable segment), while bedrock fractures was delineated beneath VES points 1, 3, 5 and 10, corresponding to distances 0, 80m, 160m and 400m respectively. The topsoil resistivity varies from 83 to 865 ohm-m, while resistivity in the weathered layer materials ranges from 182-1139ohm-m along the stable segment and 27-262ohm-m along the unstable segment. The low resistivity values observed beneath the unstable segment are typical of expansive clay. Thus the instability of the road pavement along the studied portion of the road is probably precipitated by the presence of near surface bedrock depressions, occupied by low resistivity weathered materials, typical of expansive clay and sandy clay, adjudged unsuitable construction materials.

This study was aimed at mapping the subsurface extent of saline water intrusions into aquifers at the eastern part of Dahomey basin, Nigeria. The study adopted geoelectric sounding methods. 108 vertical electrical soundings (VES) and 9 induced polarization soundings (IPS) data were acquired using Schlumberger array technique. Three aquifer units were delineated across the study area. The resistivity of the first, second and third aquifer layers varies from 0.2 to 1569 ohm-m, 0.5 to 904 ohm-m and 0.4 to 665 ohm-m respectively, while depth to the top of first, second and third aquifer varies respectively from 0.7 to 151.5 m, 1.4 to 305.5 m and 12.9 to 452.9 m. The depth to the first aquifer layer is shallow (less than 5 m) in the coastal area which makes this area to be highly vulnerable to anthropogenic pollution while their proximity to Atlantic Ocean makes them susceptible to saline water intrusion. In all the three aquifer units, the coastal area, Agbabu and other few locations in the mainland are characterized by low resistivity values (below 60 ohm-m) indicating possible presence of brackish or saline water. IP sounding results showed that all the low resistive layers in the mainland are characterized by clayey materials. The integration of VES and IPS results enabled the delineation of the saline water lateral extent across the study area. There is a strong direct correlation (r² = 0.8564) between location distance from the saline water source and depth to saline water in the study area. This can therefore serve as a predictive model to determine depth to saline water at any location within the saline water zone in the study area.

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Magnetics and Electrical resistivity methods were used in the evaluation of the subsurface integrity of a 2500 m segment of Ipinsa road off the Ilesha-Akure expressway adjacent to the Federal University of Technology, Akure, Ondo State, Nigeria in order to provide guidelines for the authority whenever the road is to be constructed. The road was investigated using geophysical prospecting methods involving Magnetics profiling and Vertical Electrical Sounding (VES) technique. The magnetic data were analysed first by taking care of diurnal variation and the results were presented as relative magnetic. The VES results were presented as geoelectric sections. The results from the two methods were stacked for easy correlation. The results from the Magnetics method study shows the presence of near-surface linear geologic structures and of varying length, depth, and altitude at different distances (350, 550, 650, 840, 870, 900, 1080 and 1160 m) and depths (5, 12, 13, 15, 15.5, 16, 17 and 19 m) respectively, which suggest the probable fracture zones that are inimical to the foundation of the road subgrade. The vertical electrical sounding survey were conducted at points of anomaly and non-anomalous zones based on the magnetic survey results. This is done to further delineate the fracture zones and correlate the results to get enough information of the subsurface. The corresponding geoelectric results delineated weathered/fractured bedrock with resistivity range of 222 - 412 Ωm at distances 650, 800 - 900 and 1080 - 1160 m along Traverses A and B. Likewise at distances 1380 - 1600 m, 2040 m, 2240 m, 2260 m and 2540 m along traverses’ C and D. The integrity assessment of the Ipinsa road network sub base lithology was successfully assessed using the geophysical modeled results and possible fractured bedrock and saturated/clayey sub soil material zones that are inimical to road stability were delineated. The research findings are valuable for precise decision in road infrastructural design.