Evaluation of specific retention, specific yield, and storage-dependent drainability efficiency in a coastal milieu via geo-electrical technology

Abstract

ABSTRACT The aim of this research was the application of geo-electrical technology in the determination of specific retention, specific yield, and storage-dependent drainability efficiency within a major coastal milieu in Nigeria. This improves on past work where expensive and time-intensive pumping tests were employed to determine specific retention and specific yield. In addition to the determination of these key aquifer geo-kinetic properties, other important aquifer characteristics such as aquifer potentiality, protectivity, and vulnerability to contamination within this major coastal system were determined. Geo-electrical technology employed Wenner and Schlumberger arrays to undertake Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) surveys and results obtained were constrained by ground truth from lithological logs. Results from the electrical resistivity surveys indicated that the lithological strata comprised motley topsoil, coarse sand, fine sand, and sandy clay. Measures of specific yield and specific retention were generated as secondary geo-electrical indices. Specific yield intersected with specific retention at 73% storage-dependent drainability efficiency (SDE), indicating that this percentage must be exceeded for optimal groundwater extraction from the rock matrix's pore spaces during pumping. Aquifer transmissivity measures indicated high aquifer potentiality; longitudinal conductance measures indicated poor aquifer protectivity implying increased vulnerability of the aquifer to contamination.