Hydrology

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Browsing Hydrology by Subject "Groundwater"

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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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    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.