GEOPHYSICAL ANALYSIS OF GROUNDWATER CAPACITY IN PARTS OF KHANA LGA, RIVERS STATE, NIGERIA, USING TPRF MODEL

Abstract

Geophysical analysis of groundwater capacity in parts of Khana Local Government Area, Rivers State, Nigeria was carried out using TPRT (an acronym for Thickness, Transmissivity, Porosity, Reflection coefficient, and Fracture contrast) model to identify productive aquifer zones for citing boreholes for community water supply. Electrical resistivity data acquired in twenty-one (21) locations using vertical electrical sounding method of Schlumberger configuration have been used to study the hydrogeological properties and groundwater storage potential of bedrock aquifers in the study area.. The data acquired were processed and interpreted using auxiliary curve matching and computer automation method to delineate the different geo-electric layers, their resistivities, thicknesses, and depths. The hydraulic conductivity, transmissivity, fracture contrast, reflection coefficient were estimated and plotted in the form of 2D maps to describe the spatial variations of these parameters in the area. The results of the study revealed the presence of three to five geo-electric layers. The geo-electric layers from top to the bottom, corresponds to the topsoil layer, lateritic layer, weathered rock layer, fractured rock layer, and the fresh basement rock. Lateritic and/or fractured rock layers were not delineated in some places. The weathered and fractured rock layers correspond to the aquifer units. The thickness of the weathered aquifer ranges from 7.4 to 59.1 m while the resistivity ranges from 8.1 to 2204.0 Ωm. The transmissivity, T_r, and hydraulic conductivity, K, range from 8.8 to 812.5 m²/day and 0.4 to 54.9 m/day, respectively. The reflection coefficient and fracture contrast map showed the presence of water-bearing fractures and shared some similarities with transmissivty and hydraulic conductivity maps. The consistencies between the overall groundwater potential map and aquifers parameters distributions maps suggest the appropriateness of the model for predicting groundwater potential of weathered rock in a basement complex area. The northern, and southern parts of the study area, having GW_P greater than 0.5 (50%), were recommended for groundwater development through boreholes drilled to a depth ranging from 50 m and above.