Abstract:
Water-bearing formations underlying Benin City and its environs in Southern Nigeria were
investigated to determine their structural characters, thickness and areal extent as well as their
respective storage parameters. The aim of this study is to investigate the subsurface
hydrogeological conditions and morphology of aquifers. The study area is underlain by the Coastal
Plain Sand of Miocene to Pleistocene age in southern Nigeria.
The methodology adopted in this study involved collection of lithologic logs from existing
forty five (45) boreholes in study area and geo-referencing of the wells’ positions. The logs were
plotted in space and the stratigraphic horizons were correlated in 2- & 3- dimensions using
SURFER, WINLOG, WINFENCE and STRATA EXPLORER which are terrain modeling
computer packages. Aquifer thickness and transmissivity (T) were calculated from profile plots.
Six 2- dimensional profile plots and one 3- dimensional panel diagram were constructed for the
area.
The major stratigraphic units in the study area are laterite, clayey sands, clay, sands and
gravelly sand. Two major aquifer horizons were found in the area and these occur as continuous
beds of the sandy formations. The upper aquifer horizon is characterized by fine to medium sandy
texture having average thickness of 31.72m, average transmissivity of 1820.23m2/day and mean
hydraulic conductivity of 54.48m/day. It generally occurs at depths between 19.58m and 55.16m
below ground surface. It has hydraulic connection with the ground surface through the overlying
materials and therefore generally occurs under unconfined conditions. The lower aquifer unit is
characterized by medium to coarse sandy texture having average thickness of 35.51m, it generally
occurs at depth between 45.27m and 100.31m below ground surface.
