Appraisal of Hydraulic Flow Units and Factors of the Dynamics and Contamination of Hydrogeological Units in the Littoral Zones: A Case Study of Akwa Ibom State University and Its Environs, Mkpat Enin L.G.A, Nigeria

Abstract

Borehole-controlled one-dimensional geo-electric data were integrated with water samples obtained from boreholes drilled near the vertical electrical sounding at 12 locations to assay the dynamic parameters of the water-bearing units in the Akwa Ibom State University and its environs. The study area, situated in the coastal fringe of littoral zones, lies within 4° 30′–4° 35′ N latitudes and 7° 30′–7° 35′ E longitudes. The geophysical results show that the area has five classes of generic curve types, namely HQ $\left( {\rho_{1} < \rho_{2} > \rho_{3} > \rho_{4} } \right)$ having 16.7% of the curves; HK $\left( {\rho_{1} < \rho_{2} > \rho_{3} < \rho_{4} } \right)$ having 50% of the curves; KH $\left( {\rho_{1} > \rho_{2} < \rho_{3} < \rho_{4} } \right)$ having 16.7% of the curves; A $\left( {\rho_{1} < \rho_{2} > \rho_{3} > \rho_{4} } \right)$ with 8.3% of the curves and QK $\left( {\rho_{1} > \rho_{2} > \rho_{3} < \rho_{4} } \right)$ with 8.3% of the curves within the water-bearing repositories, which are characterized by depth range and mean values of 54.6–84.7 m and 71.3 m, respectively. Using formation factor, fractional porosity, hydraulic conductivity, permeability, aquifer quality index and flow zone indicator (FZI), hydraulic flow units were predicted with the aid of average cementation factor and pore geometry factor estimated in previous study from cored samples cum water samples in the area. The appraisal of the hydraulic conductivity enabled the estimation of $0.3\,\upmu{\text{Hz}}$ as drift frequency or drift velocity per unit depth. This estimated value of drift frequency is considered to be very low and hence responsible for retention of pore fluid and subsequent contamination of freshwater within the aquifer system by the saltwater incurred into the aquifer systems from saline water sources during recharge. Based on FZI, two hydraulic units (HUs = 47) occupying 8.3% and (HUs = 50) occupying 91.7% of the entire water-bearing units have been delineated to conform to specific flow zone, which are important in groundwater management. Evidently, the use of stratigraphic boundaries in characterizing the groundwater units have not accounted for the facies changes in hydrokinetic attributes as a wide spectrum of values of permeability conform to a unit FZI. The estimation of hydrokinetic parameters from this method is less expensive, benign and non-invasive. The estimated properties show good correlations and in accordance with documented literatures. This attests to the validity and workability of the method. The typing of water-bearing units on the basis of hydraulic units other than geologic units that do not account for the physical and chemical facies changes is significant in the management of aquifer system in the survey area and is known to be highly susceptible to contaminations from ingress of saltwater into its freshwater geologic units as well as contaminations from other sources.