TITLE:
Seepage Investigation on an Existing Dam Using Very Low Frequency Electromagnetic (VLF-EM) Methods: A Case Study of Shagari Earth Dam, Sokoto, North Western Nigeria
AUTHORS:
U. Z. Magawata, D. S. Bonde, B. U. Abdullahi, Basiru Qudus, M. N. Yahaya
KEYWORDS:
Overburden, Interfaces, Occurrence, Heterogeneity, Embankment
JOURNAL NAME:
International Journal of Geosciences,
Vol.11 No.2,
February
17,
2020
ABSTRACT: Very low frequency
(VLF-EM) was used to assess variations in overburden composition, bedrock
lithology and the hidden Sedimentary structures within the foundation of
Shagari Dam of the sedimentary basin of Northwestern Nigeria. Four
VLF-electromagnetic (EM) traverses were occupied at 10 m in-tervals. The VLF
normal and filtered real component irregularities identify major geological
interfaces suspected to be faults/fractured zones. The points of crossover
between the real and imaginary components delineate the fractured zones, which
were identified as areas of possible seepage (sloughing and piping). The fractured
zones are suspected to be present at all traverses. In total, 38 fractured
zones were identified along the dam embankment and canal site, while 17 major
fractures occurrence dippers along the Traverses at a point, Traverse 1 (F3,
F4, F5, F7, F10, F11),
Traverse 2 (F12, F13, F21, F22),
Traverse 3 (F23, F24, F29) and Traverse 4 (F32,
F33, F34, F38), and coincide with cross over
point at 4 traverses. These seepage zones cause heterogeneity in the sub-surface
structure that could be prime to dam failure which in turn leads to the
flooding, decreases in irrigations activities of the peoples leaving around the
dam and loss of several hundreds of life when care not taken. The result of the
study suggests that VLF is suitable for observing seepages in embankment dams.