Abstract:
Geophysical investigation has been undertaken to determine the cause(s) of a dam failure
at the College of Education, Ikere Ekiti. The area is underlain by the Precambrian
Crystalline Basement Complex rocks of Southwestern Nigeria with the lithology consisting
mainly of Older granite and Fine-grained biotite granite. The geophysical methods adopted
for the study are magnetic, electromagnetic, electrical resistivity and Spontaneous Potential
(SP). Traverses were established both parallel (T1, T2, T6, T7) and perpendicular (T3, T4,
T5) to the azimuth of failed dam axis. The field data were processed and filtered using
suites of software which include Oasis montage™, 2D Euler deconvolution, Diprowin,
Winresist and Karous Hjelt, thus, enabling qualitative and quantitative
evaluations/interpretations. The results are presented as profiles, sections, charts, tables and
maps. The magnetic profiles delineated various anomalies with notable positive amplitudes
ranges from 65 to 400 nT and notable negative amplitudes ranges from -20 to -250 nT.
Electromagnetic profiling shows dominant high conductivities on T2, T4, T5 and T7
indicating potential fractures/water saturating media. Dipole-dipole results revealed the
existence of some discontinuities along some traverses. The geoelectric layers delineated
are the topsoil (57 to 1938 Ω-m), weathered layer (31 to 774 Ω-m), partly
weathered/fractured basement (80 to 811 Ω-m), and the fresh basement (1900 to ∞ Ω-m).
SP troughs with maximum amplitudes ranging from -6 to -75 mV along T1, T2, T4, and
T5 are indicative of some streaming potentials possibly occasioned by fractures/faults. The
magnetic, and resistivity studies indicate shallow basement with depth to bedrock ranging
from 0.8 to 20 m. The major fractured zone delineated within the study area extends from
the northwestern upstream region, transverses T5, T4, and terminates at T2. These
identified structures strike parallel to the dam axis and are confined to the central area of
the reservoir and apparently cannot constitute the major medium for the reservoir leakage.
Since the results obtained at T1 and T6 (dam embankment) do not show signatures
indicative of shows that no seepage path exists beneath the dam. This study has shown that
the failure of the dam cannot be ascribed to geological factors, thus the failure may have
been due to other factors presumably associated with construction.
