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    Identification of potential groundwater recharge zones: a case study of KwaZulu-Natal, South Africa
    (University of Zululand, 2022) Ponnusamy, Dennisha
    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.
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    The flow and sediment of the Mlalazi estuary in Kwazulu-Natal, South Africa
    (University of Zululand, 2021) Mmako, Lesiba Vincent
    The catchments and estuaries are fragile systems that are prone to serious degradation from many different anthropogenic impacts (e.g. flow abstraction/diversion, sand mining, soil erosion etc.). In South Africa, many of the anthropogenic impacts on estuarine systems are generally derived from subjective expert opinions that are not supported by hydrodynamic data (Rasifudi, 2019). River flow is one of the main factor that control the dynamics of many estuaries worldwide (Zhou et al., 2014). It is important to understand the water flow depth, direction and velocity in estuaries since they affect and control the erosion, transport and deposition processes of alluvial sediment and nutrients. The Mlalazi Estuary is one of the best conserved estuaries situated along the eastern shoreline of the Kwa-Zulu Natal Province of the Republic of South Africa (RSA). This Estuary is classified as a Temporarily Open/Closed Estuary (TOCE). There is limited observe hydrological data that can be use to improve the decision making process within the Mlalazi Estuary in future. Therefore, a numerical model is useful tool to derive best estimates of flow dynamics and sediment transport. This study investigated the flow dynamics associated with fluvial events within the Mlalazi Estuary resulting from Q2yr, Q10yr, Q20yr, Q50yr and Q100yr flood return periods. The hydraulic modelling software, HEC-RAS (version 5.0) flow model, aided by GIS (HEC-geoRAS), was used to obtain estimates of the flow velocity and water level (depth) within the Mlalazi Estuary and floodplain. Available geometric data (DEM + bathymetry) was used to generate 174 river cross-section profiles at different interval spaces ranging from 60m to 200m along the Mlalazi Estuary. The Mlalazi run-off data simulated from the hydrologic model HEC-HMS (Rasifudi, 2019) was used as an upstream boundary condition. The model was calibrated and validated using the historical data from the 1987 flood survey and continuous water level data from monitoring sites established in 2015 by the Hydrological Research Unit of the University of Zululand. The hydraulic model gave satisfactory performance statistics for high flood events during calibration and validation periods. The model overestimated the Q2yr stage and velocity event in the upper estuary channel and underestimated the stage and velocity in the lower estuary channel. The simulated velocity and Hjulström-Sundborg diagram were used to analyse the fluvial sediments distribution in the estuary channel and floodplains. The inundation maps of different storm sizes revealed that erosion occurs mainly in the active estuary channel and deposition of alluvial sediment takes place on the floodplains. The study concluded that a physically based, numerical flow model is best method for providing reliable estimates for hydrodynamic data and information in estuaries with limited observed data like the Mlalazi Estuary. The study will also provide essential flow information needed to set up the Mlalazi Mouth Model, which will help to determine the ‘flow reserve’ of the Mlalazi Estuary.
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    Assessment of coastal aquifer contamination using geochemical and health risk assessment in Maputaland formations, South Africa
    (University of Zululand, 2021) Mthembu, Philisiwe Promise
    The Maputaland coastal plain of KwaZulu-Natal is among the popular tourist areas in South Africa. Groundwater is the foremostsource for drinking and irrigation abstracted from the unconsolidated aquifers where the infiltration rate is very high. This could possibly increase the risk of aquifer contamination.The main objectives of this study is to evaluate the hydrogeochemical processes, identify the intended sources of groundwater contamination, and understanding the extent of trace metal contamination and health risk assessment. In this study, 53 and 42 groundwater samples were collected from bore wells during 2018 and 2019 and were analysed for major ions, minor ions, nutrients and trace metals. Na-Cl water type was dominant in groundwater followed by Ca-HCO3. Cross plots revealed that ion exchange, reverseion exchange, silicate weathering, seawater mixing, and anthropogenic inputs from agricultural activities govern the groundwater chemistry. GIS methods were adopted to produce spatial distribution maps of major ions through which locations of groundwater contamination and the intensity of hydrogeochemical processes were identified. The water quality index (WQI) varied from 18.9 to 157.1 with an average value of 45.55. Majority of the samples are classified as good, 22 % as poor, 2 % as very poor and 7% under unsuitable category, which are spatially distributed towards the southern and western parts of the study area. Mean concentration of trace metals were in the order: Zn>Li>Al>Fe>Mn>Cu>Pb>As>Co>Cd in 2018 , Fe>Zn>Mn>Sr>B>Pb>Cu>Co>Cr>Cd>Ag>Al>Ni in 2019. Most of the trace metals were found to be within the WHO standards for drinking water except for Cd, Zn, Pb, Mn, Al and Fe. Health risk assessment of trace elements via ingestion and dermal absorption pathways was carried out. Hazard quotient through dermal absorption (HQdermal) and hazard index (HI) for Co and Mn were above 1 in adults, children and infants. HQ derma land HI for Cd was greater than 1 in children and infants. HQ derma land HI for As and Pb were greater than 1 in infants. This implies that these metals pose serious adverse risk on local people and infants are more vulnerable to health risk than children and adults. The heavy metal pollution index shows that the groundwater samples vary from low to high pollution class and 21% of the samples exceed the critical limit of 100 implying that they are highly polluted with respect to heavy metals and are unfit for human consumption. The heavy metal evaluation index and degree of contamination reveal that all the groundwater samples have low pollution with regards to heavy metals and are suitable for human consumption. Moreover, the results of ecological risk assessment reveal that the studied heavy metals pose low ecological risk. Based on the pollution index of groundwater, majority of the samples fall in the insignificant pollution zone. The synthetic pollution index reveal that 2%, 74% and 24% of the samples are suitable, slightly and moderately polluted respectively with heavy metals. Similarly, the overall index of pollution reveal that majority of the samples are excellent and suitable for drinking purpose. Multivariate statistical analysis were adopted to evaluate sources of heavy metals in groundwater. Correlation matrix and principal component analysis reveal that weathering of aquifer matrix and anthropogenic activities are accountable for the release of heavy metals into groundwater. Furthermore, R-mode and Q-mode cluster analysis revealed two clusters. All the clusters from R-mode and Q-mode cluster analysis are linked to mixed sources including weathering and anthropogenic activities. This study provides the baseline data on hydro geochemistry that can be utilised further in future studies. It is recommended that contaminated groundwater in this region be treated before utilisation in order to maintain the sustainability of public health and recommends for further extended studies.
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    Groundwater geochemical characteristics and its suitability for drinking and irrigation in Ventersdrop, North West Province, South Africa
    (University of Zululand, 2019) Mubva, Khuliso Virginia; Elumalai, V.
    Groundwater is major source of freshwater in regions devoid of surface water resources. The dependence on groundwater is increasing worldwide. South Africa is no exception. Groundwater resource has been identified as the main and reliable water resource for human consumption and agricultural practice in the Ventersdorp area, South Africa. Assessment of groundwater quality is necessary for safe usage for drinking and for irrigation purposes so as to boost the socio-economic wellbeing of the region. One such study was taken in Ventersdorp area, Schoonspruit Catchment, South Africa. The groundwater samples were collected from forty boreholes in 2015 as well as seventy boreholes in 2017 and was analysed for major ions and nitrate. The physical and chemical parameters of groundwater namely EC, pH, TDS, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-and NO3- during 2015 and 2017 were analysed. The concentration of major ions chemistry in groundwater was within the permissible limits of South African National Guidelines and World Health Organisation and for drinking use. The overall pH values for both sample periods represent slightly acidic to alkaline in the study area. Based on DWAF (1996) approved limit of drinking (EC <450), 45% of groundwater samples in 2015 and 13% samples in 2017 exceeded the limit in the study area. The classification of groundwater based on total hardness (TH) in the study area shows that majority of groundwater samples fall within the hard water category and the major groundwater types were Ca–HCO3 and Ca-SO4. The affluence of the major ions in the groundwater of the study area was found to be in the order of Ca>Na>Mg>K and HCO3>Cl> SO4>NO3. Several correlation diagrams between the major ion and other plots like the Gibbs, Chadha, Piper, Durov’s were prepared to ascertain the sources of ions in the study area. Gibbs plots have revealed that groundwater in the study area for both year 2015 and 2017 is of rock water interaction dominance. Similar inferences were obtained from Chadha plot. High correlation between calcium and bicarbonate, chloride with sodium, nitrate and sulphate and nitrate and potassium. Further, in order to ascertain the irrigation water quality, Kelly’s ratio, Sodium percent, residual sodium carbonate, sodium absorption ratio and permeability index were calculated for the groundwater samples in the study area. The IWQI as well as DWQI was calculated to get a snap shot of the region and it confirmed that most of groundwater samples in the study region fall between the range of suitable for both drinking and irrigation purposes in 2015 and 2017. The impact of heavy metal pollution index (HPI) in groundwater was ascertained. The coefficient variation of Zn was found to be higher than that vii of Cu, Cr, Cd, Ni and Pb in groundwater of the study area. The results suggest that Zn concentration has a high probability of being influence by human activities. Apart from this groundwater quality, rainfall data and groundwater level data from 1974 to 2014 was collected from National Department of Water and Sanitation of South Africa. The analysis of the data revealed that shallow aquifers are easily affected by local climate changes while deep aquifers are dependent only on regional changes. Thus, shallow aquifers are more vulnerable to climate variability. The recharge of shallow aquifer is brief as compared to recharge of deep aquifer. In the study area, shallow wells are more likely to be affected by irrigation flow compared to deep wells and inferred from high correlation between Ca and HCO3. Cl was correlated with K and Na. NO3 and Cl are highly correlated. Variables correlating with Cl, SO4 and NO3 are partly derived from agricultural activities. Nitrate concentration in the study area shows strong positive relationship with five major ion and EC for last three decades from 1994 to 2014. In general, the quality of groundwater is suitable for both drinking and irrigation needs. This study helped to comprehend the present state of groundwater chemical composition in Ventersdorp and to assess its fitness for irrigation and drinking uses.
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    The hydrochemical characterization of the Mgobezeleni catchment in Sodwana Bay
    (University of Zululand, 2019) Mkhwanazi, Millicent N.; Simonis, J.J.; Bate, G.
    The Maputaland region comprises one of the world's most remarkable areas of biodiversity and aquatic systems. It also has the largest primary aquifers in South Africa, constituting 25% of all coastal plain aquifers found in the country. The increasing number of rural households’ development along the Maputaland coastal plain pose significant eutrophication risks on the hydrological system, owing to the use of informal sewage management facilities. To understand the anthropogenic impacts on the hydrological system the Mgobezeleni catchment was selected in this study as it represents a microcosm of the Maputaland region. The Mgobezeleni Estuary is connected to the two lakes (Lake Mgobezeleni and Lake Shazibe), and large swamp forest, and mouth is affected by tidal influence. The hydrological system in the catchment is directly controlled by the groundwater system. The overlying paleo-dune sands are permeable permitting high percolation of the annual rainfall. The catchment is dominated by three aquifers namely, the uppermost KwaMbonambi Formation, Kosi Bay Formation and Uloa Formation. The water table is dynamic, affecting the dimension of the unsaturated zones, the hydraulic gradient and the groundwater flow in the aquifers. The groundwater recharge only becomes visible as base flow in surface water resources after several years. Contaminants that have accumulated over decades are therefore still present in the aquifers, being restricted mainly in the upper KwaMbonambi Formation. Therefore, leaching of nutrients from the informal sanitation systems pose adverse impacts on the groundwater chemistry, which in turn can result in eutrophication of surface water resources. The growth in population in the Mgobezeleni catchment has therefore increased the nutrient load in the groundwater system due to the presence of confining layer that restricts nutrients to the shallow aquifer. Nutrients are relatively elevated in groundwater close to highly populated areas such as Mbazwana. Moreover, the discharge of groundwater as a base flow component in surface water resources (lakes, estuary and wetland) causes the eutrophication (growth of dense macrophytes and microalgae, including toxic cyanobacteria species) due to high nutrient composition. The dense macrophytes species together with the cultivated peat, are decomposing to produce high levels of dissolved OM with humic substances (humic acid and fulvic acid) causing the blackwater in the surface water resources and also increasing the population of microalgal species. The water in the catchment is generally characterized by a sodium-chloride ions signature with relatively low Ca, Mg, K, and SO4 concentrations. It is generally high in Al, Fe and Mn concentrations. vi The high levels of nutrients and planktonic algae in hydrological system threaten the ecological system in the Mgobezeleni catchment. The presence of the bacteria Microcystic aeruginosa can affect the domestic and wildlife including the water supply to Ezemvelo KZN Wildlife’s residential areas. In addition, the cultivation of peat in the Mgobezeleni catchment causes the peat to decompose, thus also increases the N and P concentrations and OM content in the wetlands which are also influencing the water quality in the lakes and estuary.