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- Urbanization has accelerated changes in the quantity and stability of the water resources in the uMhlathuze watershed of KwaZulu-Natal. This study applied the use of GIS and remote sensing to demarcate groundwater potential recharge zones in the uMhlathuze catchment using AHP approach and Catastrophe theory by assigning weights to 10 parameters with their sub-criteria and the results were validated against groundwater quality data. It was discovered that 22.92% and 26.38% of the catchment is encompassed by ‘Low’ groundwater potential recharge zones, 0.37% and 0.08% by ‘Very low’ groundwater potential recharge zones, 9.42% and 10.26% by ‘Good’ groundwater potential recharge zones, 66.87% and 63.19% by ‘Moderate’, and 0.42% and 0.09% by ‘Very good’ for AHP and Catastrophe theory respectively. The resultant map demonstrated that recharge potential of groundwater is lowest in mountainous regions coupled with hard rock geology of low transmissivity, whereas the highest potential prevails in lower slopes and plains with more permeable soil. The findings of the validation revealed that the lowest and highest total dissolved solid, nitrate and groundwater level overlaps with the ‘Good and Very good’ and ‘Low and Very low’ groundwater potential recharge zones respectively. From the collective findings of this study, it is inferred that the convergence and use of GIS and remote sensing for delineating the groundwater potential recharge zones are effective. The study further recommends that this method can be applied in research/projects involving the implementation of artificial groundwater recharge structures for better groundwater planning and governance.
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- The sources of chemical constituents of groundwater and its associated hydrogeochemical processes in the part of Mhlathuze catchment was identified. Groundwater of the area is classified into soft to very hard and the nature is identified as acidic to alkaline. The overall electrical conductivity is < 3000 μS/cm except in three wells. The predominant water type is NaCl (69% of samples) and CaMgCl facies. Gibbs plots, mCa/Mg ratio, mNa/Cl ratio, Ca + Mg vs HCO3+SO4 plot, Na + K vs HCO3 plot, Ca/Na vs HCO3/Na, Chloroalkaline indices (CAI 1, CAI 2) and Ca + Mg–HCO3–SO4 vs Na + K–Cl plots confirm the impact of silicate, carbonate mineral weathering and ion exchange reaction in this aquifer. However, few wells are influenced by the evaporation process. Groundwater is highly undersaturated with sulphate, chloride minerals and saturated with carbonate minerals. CA revealed that Cl and SO4 are derived from anthropogenic sources and a significant positive correlation between HCO3 and Cl reveals that wastewater recharge has most likely simulated the mineral weathering in the vadose zone, which could have further enhanced HCO3 and Cl in the aquifer. PCA resulted in three factors. Factor 1 defines the influence of geogenic and anthropogenic processes while Factors 2 and 3 imply the mineral weathering and nitrification processes. Hierarchical cluster analysis defines that evaporation, anthropogenic input, silicate and carbonate weathering and nitrification process are the sources of chemical constituents of groundwater in this aquifer.
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