Browsing by Author "B. A. Ojulari"

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    Assessment of saltwater–freshwater interactions using water samples and borehole logging information in the Lagos coastal region, Nigeria
    (Environmental Earth Sciences, 2021-07-27) M. A. Yusuf; B. A. Ojulari; K. O. Ibrahim; T. A. Abiye
    An analysis of borehole logs with hydrophysical data from the Lagos coastal belt, Southwestern Nigeria, was carried out to evaluate the subsurface lithological units and geo-environmental impact of seawater intrusion into coastal freshwater. Forty f ive (45) borehole logs, consisting of natural gamma, electrical resistivity log and hydrophysical parameters were integrated to delineate saline and fresh aquifer zones and propose simplified conceptual models for adequate groundwater characterisation and development. The qualitative interpretation of the borehole logs revealed a complex lithology of alternating sequences of sand and clay layers. The study also showed that the subsurface was variably intruded by saline water indicated by low resistivity values with freshwater/saline water boundaries occurrence at depths ranging between 14 and 157 m from west to east. The variation in depths of occurrence of freshwater/saline water interface is dependent principally on the proximity to saline/brackish water source as well as variation in lithology. Complementarily, the average electrical conductivity (EC) of 1770 μS/cm (GW1–7) and 1676 μS/cm (GW8–13) recorded in groundwater at Apapa in the west and Island at the central part, respectively, further confirmed saline incursion of the coastal aquifers in the region. This study demonstrates versatility of geophysical borehole logs in identification and differentiation of the subsurface lithology and its fluid content.
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    Geo-Electric Assessment of Kali Failed Dam Project Aliero, North Western Nigeria
    (International Journal of Geosciences, 2020-08-27) U. Z. Magawata; Ibrahim Mohammed; B. A. Ojulari; A. I. Augie; Salisu Musa
    An integrated geophysical investigation using very low frequency electro magnetic (VLF-EM) and electrical resistivity methods using (VES) technique has been carried out for investigation of possible causes of dam failure in Kali, Aliero Northwestern Nigeria. A total of Three 3 (VLF-EM) traverses and Ten 10 vertical electrical soundings (VES) techniques have been carried out to identify the fracture zones, seepage and possible threat that lead to the col lapse of the dam. The interpretation of VLF-EM data is carried out qualita tively using Fraser and Karous-Hjelt filters and the interpretation of sounding data is done using IPI2 win software. VLF-EM data signifies the exact fracture zones founded on higher values of relative current density that coincide to the subsurface fracture. The survey was conducted on an interval of 10 m interval along traverses at South-North direction ranging from 620 - 640 m in length. The plot of filtered real and filtered imaginary identified noticeable fracture zone close to the surface which was later further delineated by (VES) tech nique. VES soundings were carried out at locations of prominent VLF ano malies presumably typical of basement fracture using AB/2 of 80 m. Results interpreted show layers thickness and their corresponding resistivity, top soil (0.5 m to 3.45 m, 51.9 Ωm to 318 Ωm), underlain by clay to confined clay (4.56 m to 54 m, 7.88 Ωm to 60.2 Ωm) which is underlain by fractured/fresh basement (5.76 m to 73.9 m, 40.3 Ωm to 197 Ωm). The overburden materials underlain are far away to subsurface (bed rock) in most of the area to support the dam. The clay materials which could serve as conduit, exist within the shallow overburden which was not excavated during the construction. Therefore it was concluded that the dam cannot retain its strength to oppose the dam against collapse.