Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria |
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| Authors: | A A Adepelumi B D Ako T R Ajayi O Afolabi E J Omotoso |
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| Institution: | (1) Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria;(2) Department of Physics, University of Lagos, Lagos, Nigeria |
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| Abstract: | Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration
into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic
system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity
(VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between
1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity
curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of
four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between
125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond
to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish
groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities
values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation
are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion
into the aquifers can be accurately mapped using surface DC resistivity method. |
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| Keywords: | Resistivity Coastal Saline water Aquifer Nigeria |
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