Groundwater Potential Zones Assessment Using Geospatial Models in Semi-Arid Areas of South Africa

Abstract

Water resources are under tremendous pressure as a result of the growing demand for water to meet human needs. Hence, it is necessary to delineate groundwater potential zones (GWPZs) to sustainably develop and manage groundwater resources. In this study, the geospatial-based analytical hierarchy process (AHP) and frequency ratio (FR) techniques were used to identify the GWPZs. Seven factors (geology, rainfall, slope, lineament density, soil, drainage density, and land use/land cover), which partially or entirely influence the groundwater potentiality of an area, were accessed separately and later combined to create GWPZ maps. Weights and ranks were assigned to the factors to perform the AHP model using existing knowledge. The FR was performed by calculating the percentage ratio between the dependent variable (boreholes) and the independent variable (factors). The preparation of the contributing factors and the creation of the resulting models was done using ArcGIS 10.8. The final GWPZ maps were classified into five zones: very low, low, moderate, high, and very high. About 80 boreholes in the study area were randomly subset into training and testing datasets; 58% were used for model training, and the remaining 42% were used for validation purposes. The receiver operating characteristic (ROC) curves for the GWPZs models were generated, and the areas under the curves (AUC) were calculated. Validation of the models shows that the FR model is more efficient (85.3% accuracy) than the AHP model (83.2% accuracy). The findings show that the AHP and FR models are reliable and can be adopted to characterize GWPZs in arid or semi-arid environments.