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Geophysical investigation of saline water intrusion into
freshwater aquifers: A case study of Oniru, Lagos state
L.
Adeoti1, O. M. Alile2* and O.
Uchegbulam3
Department of Physics, University of Lagos, Akoka, Lagos,
Lagos State,
Nigeria.
Department of Physics, Covenant University, Ota, Ogun State,
Nigeria.
Department of Physics and Energy Studies, Western Delta
University, Oghara, Delta State, Nigeria.
*Corresponding author. E-mail:
owenalile@yahoo.co.uk.
Accepted 5 January, 2010 |
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A total of five electrical imaging lines were measured using
the wenner configuration. And a total of twelve VES was
carried out within the area of investigation. The lines were
aligned almost in a linearly NS azimuths, perpendicular to
the ocean. The results were presented as profiles,
multi-profiles, maps, pseudo sections and inverted sections.
Interpretations of these results involve both qualitative
and quantitative deductions from 1D and 2D geoelectric
models. WingLink software was utilized for plotting,
filtering, modeling and iterations of the resistivity data.
From the quantitative interpretation and nearby well log
data five distinct layers were identified. The layers are
dry and unconsolidated sand, clayey sand, saline sand,
saline clay and freshwater sand. The resistivity of the
topsoil varies from
3259.59 Ohm-m on VES 2 - 67.04 Ohm-m on VES 12.
The resistivity of the freshwater sand varies from
1649.76 Ohm-m on VES 6 - 158.28 Ohm-m on VES 10.
The resistivity
of the saline layer (saline sand/clay) varies from
2.06 Ohm-m on VES 12 - 39.88 Ohm-m on VES 3.
The depth to saline/freshwater interface varies from
12.97
m on VES 8 -
63.01 m on VES 5.
The quality of groundwater varies from poor polluted saline
water saturated sand/clay through intermediate water quality
clayey sand/sand to freshwater sand. The interpreted results
show saline water plumes where they occur in different part
of the area investigated. The 1D and 2D results correlate to
a very high degree indicating saline water intrusion between
depth interval of 13 and 64 m in the study area. Two major
freshwater aquifers (shallow < 6 m and deep > 60 m) where
delineated with most of them occurring unprotected. The
results showed the effectiveness and usefulness of
electrical resistivity and induced polarization method in
mapping saline water intrusion problem in coastal areas.
Key words:
Geophysical investigation,
saline water,
aquifers,
coastal terrain. |
