DEVELOPMENT OF DRASTICLYS MODEL FOR GROUNDWATER VULNERABILITY MAPPING WITHIN THE AKURE METROPOLIS

Abstract

Groundwater vulnerability to contamination risk is conceptualized in this study by evolving a novel vulnerability modeling with a view to enhance groundwater management resources sustainability within Akure metropolis. The vulnerability modeling technique christened “DRASTICLYS” is a modified version of the renowned DRASTIC model. Database consisting of different data sources including hydrogeological, geophysical, remote sensing, weather and geochemical were utilized for the model development. Extracted from the created database were the derived pollution potential conditioning parameters (PPCPs) namely Depth to Water Table (D), Net Recharge (R), Aquifer Media (A), Soil Media (S1), Topography (T), Impact of Vadose Zone (I), Hydraulic Conductivity (C), Lineament Density (L), Borehole Yield (Y) and Longitudinal Conductance (S2). From the two hundred and seventy-nine (279) depth soundings conducted in the study area, fourteen (14) curve types, which had the H curve type predominant (90%) were obtained. The produced pollution potential conditioning parameters themes were weighed and ranked using the mechanism of Analytical Hierarchy Process (AHP) technique under Multi Criteria Decision Analysis (MCDA) to adapt the model to the study area. The criteria weights generated were used to develop DRASTICLYS vulnerability index modeling algorithm used to produce DRASTICLYS Groundwater Vulnerability Prediction Index Map (GDVPIM) for the area. The map enabled the zoning of the study area into five groundwater vulnerability potential zones of no vulnerability, very low vulnerability, low vulnerability, moderate vulnerability and high vulnerability. The DRASTICLYS model results show moderate to high vulnerability in the central portions and eastern flank of the area. The efficiency of the developed DRASTICLYS model against the conventional DRASTIC method was evaluated using geochemical data. The geochemical analysis results show that the central portion of the study area is poorly protected. Success accuracy of 95% and 90% for the DRASTICLYS and DRASTIC models were obtained. Statistical analysis conducted on both models correlated satisfactorily with geochemical results. The results showed 78% and 74% for the DRASTICLYS and DRASTIC models respectively. Thus, DRASTICLYS model proves more efficient and reliable than the conventional DRASTIC model. This model constitutes an implementable template for use in similar terrains and thus serves as a guide to planners and managers of groundwater resources