Identification of potential groundwater recharge zones: a case study of KwaZulu-Natal, South Africa
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Date
2022
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Publisher
University of Zululand
Abstract
Urbanization has accelerated the changes in the uMhlathuze watershed in Kwazulu-Natal resulting in a deterioration in the quantity and stability of water resources, hence calling upon the development of groundwater resources. This study combined the use of GIS and remote sensing to demarcate groundwater potential recharge zones in the uMhlathuze catchment and Maputaland region using various pertinent parameters. The AHP approach and Catastrophe theory were used to determine acceptable zones by assigning weights to the 10parametersand their sub-criteriafor the uMhlathuze catchment, whilst the potential groundwater zones of the Maputaland coastal plain of Kwazulu-Natal is identified by comparing the Analytic hierarchy process (AHP) –Multi-criteria decision-making (MCDM) technique and Boolean logical approach. The map of groundwater potential zones for Maputaland was prepared by assimilating the 8 thematic layers, i.e., geology, geomorphology, lineament density, soils, slope, rainfall, and land use. Each thematic layer were assigned with subjective relative weights under AHP-MCDM technique and Boolean logic and were overlaid in a GIS platform to identify the groundwater potential zones. The groundwater potential zones were delineated under two different GIS techniques to obtain confident results. Weights of thematic layers were allocated using AHP normalized eigen vector methodology and weighted linear combination method was employed to find the groundwater potential index. Whereas in a Boolean approach, AND operator was applied in order to integrate thematic layers to delineate the groundwater potential zones. The AHP and the emerging Catastrophe theory was applied to the drainage density, geology, morphology, lineament density, soil type, rainfall, land use/land cover, transmissivity and aspect parameters and their sub-criteria for the uMhlathuze catchment and then integrated in a GIS environment. The Catastrophe theory consisted of firstly standardization of the parameters and sub-criteria, followed by the normalization of values using the complementary principle according to the model type and mathematical function encompassed by the model. Once they were normalized the highest mean value of the parameters were assigned the highest factor weight, whilst the lowest mean value was assigned the lowest factor weight. The delineated groundwater potential maps using AHP-Boolean-MCDM technique for Maputaland indicates that 6.0% (310.5 km2) from total area falls under very good; 67% (3467 km2) good; 25% (1294 km2) poor and 2% (103.5 km2) under very poor, whereas in Boolean 6logic about 70 % of the area (i.e.,3623 km2) constitutes good and 30 % (1552 km2) of the areas constitutes poor groundwater potential zone and the for the uMhlathuze catchment 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 the AHP and Catastrophe theory respectively. Further, the obtained results in Maputaland indicate that the geology, geomorphology, land use and slope played a vital role in groundwater recharge. This pioneer study in Maputaland coastal plain explores the baseline data of the potential groundwater zones. Furthermore, in the uMhlathuze catchment, it was deduced that due to the hard rock complexion of the catchment, this attribute significantly limited presence of ‘Good’ and ‘Very good’ zones. The resultant groundwater recharge potential recharge zones maps were validated against TDS and nitrate concentrations, and groundwater level data of boreholes in the study area. It was revealed that the lowest and highest TDS, nitrate, and groundwater levels overlap with the ‘Good and Very good’ and ‘Low and Very low’ groundwater potential recharge zones respectively. The results emanating from this study can be used in further understanding of the available groundwater resources and can be helpful in future to find suitable groundwater exploration sites in the area. It was inferred that the convergence and use of GIS and remote sensing for delineating groundwater potential recharge zones are effective and may be utilized for groundwater planning and governance.
Description
A thesis submitted to the Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Maters of Science in the Department of Hydrology at the University of Zululand, South Africa, 2022.
Keywords
Groundwater, groundwater resources, recharge zone, Maputaland coastal plain