Joseph I. Amah, Elizabeth I. Okoyeh and Solomon O. Onwuka
The hydraulic parameters and hydrostratigraphy of the thick Cretaceous aquifers namely; the Upper Maestritchtian Nsukka Formation, and the Middle Maastritchian Ajalli Sandstone Formation were computed and geostatistically analysed in this paper.The two aquifers belong to the same hydrostratigraphic units in that they exhibit similar hydraulic characteristics with similar lithologies at depths where regional saturation occurs The hydraulic conductivity (K), Transmissivity (T) and specific capacity of the boreholes when correlated from layer to layer showed high spatial variability. Transmissivity (T) is highly variable from 35m2/day around the southeastern boundary at Diogbe to 2219.17m2/day at Ibagwa-aka. The hydraulic conductivity varies from 0.56m/day to 30.52m/day following the same trend. The hydraulic conductivity field shows a highly heterogeneous layering pattern when referenced to a vertical stratigraphic column with an equivalent horizontal conductivity Kx 0f 9.28m/day and vertical hydraulic conductivity Ky of 5.86m/day, giving an anisotropy factor of 1.58. The Nsukka and Ajalli Formations are considered by this research report to be homogeneous but anisotropic consisting of at least five hydrostratigaphic units of about 50m layer thickness laid in succession .The asymptotic longitudinal dispersivity (AL) of the sequence is estimated at 30.5m.The layer within 120m-220m above sea level is the most prolific layer. The utility of this research lies in the understanding of the producing zones of the sequence, parameter estimates for aquifer management ,hydrodynamic dispersion studies and contaminant modelling in the area.
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