Mathematical Modelling of Groundwater Flow System of a Water Table Aquifer in Nsukka Area, Southeastern Nigeria

ABSTRACT Two main geological formations outcrop in the area which is within latitudes 6"45'N-7"00tN and longitudes 7O15'E - 70301E, being part of the Anambra basin of southeast Nigeria. These are the Ajalli Sandstone that is of Middle Maastrichtian age covering most of the area and the Nsukka Formation of Upper Maastrichtian age that is less prominent and overlies the Ajalli Sandstone. These two formations belong to the same hydrostratigraphic unit and give rise to thick and extensive water table aquifers. Mathematical models of the regional flow system in the area were made using data from over thirty boreholes in the area. A graphical solution of Laplace equation was achieved by I construction of a map of the hydraulic heads and flownet for the area. Analytical solution was achieved for specified flow cell by direct integration while numerical solutions of Richard's and Poisson's equations were carried out using computer software ASMWIN (Aquifer Simulation Model for Windows) for the entire domain. Aquifer constants derived from pumping test analysis using Cooper-Jacob's method were used as input data for the numerical simulations. Two flow systems exist in the area. The fust is an upper localized perched system (LPS) resulting from the entrapment of vertical flow through the regolithic Nsukka Formation by the underlying .