Using Geospatial Techniques and Analytic Hierarchy Process to Map Groundwater Potential Zones.

Abstract

This study is conducted in Luvuvhu River Catchment (LRC) of South Africa, which has numerous major agricultural farms that are located in the upper catchment, especially in Levubu Valley. The significant irrigation developments in upper catchment have resulted in a decrease in the yield of surface water resources to such an extent that these resources struggle to meet domestic and industrial demand. The aim of this study is to delineate groundwater potential zones (GWPZ) as a way of establishing alternative water resources to relieve the overly stressed surface water resources. Various datasets are processed to extract groundwater controlling factors. Map layers of controlling factors are assigned weights according to their relative importance to groundwater occurrence using analytic hierarchy process and then integrated based on weighted sum analysis to generate GWPZ map. Rainfall infiltration breakthrough (RIB) and area under curve (AUC) are used to validate the GWPZ map. GWPZ map shows that lower catchment has very high groundwater potential covering about 409 km2 . Nonetheless, about 50% of LRC spatially falls within high groundwater potential zone. Groundwater recharge, based on RIB for three boreholes, that is, A9N0007, A9N0008, and A9N0018 around Levubu Valley is estimated at 8.3, 15.4, and 16.2%, respectively. Boreholes A9N0018 and A9N0018 correspond to moderate to high groundwater potential zone, whereas A9N007 coincides with low to moderate zone. Considering the groundwater recharge estimates and associated potential zones, RIB results correspond well with GWPZ map. Also, an AUC, based on 26 boreholes, of 70.9% is achieved; thus, indicating a reliable model.