Doctoral Degrees (Institute for Groundwater Studies (IGS))

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Browsing Doctoral Degrees (Institute for Groundwater Studies (IGS)) by Advisor "Vermeulen, Danie"

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    Evaluation of the vulnerability of selected aquifer systems in the Eastern Dahomey basin, South Western Nigeria
    (University of the Free State, 2015-01) Oke, Saheed Adeyinka; Vermeulen, Danie; Gomo, Modreck
    This study aimed to evaluate the vulnerability of the shallow aquifer systems of the Dahomey Basin and formulate a simple vulnerability method with which data limited areas (which include the shallow unconfined aquifers in the Dahomey Basin) can be predicted. The Dahomey Basin is a transboundary aquifer which extends from Ghana to the western parts of Nigeria. The study covered the eastern section of the basin. The methodological approach involved a source–pathway–receptor vulnerability model. The Dahomey Basin was characterised through the geophysical, hydrological, litho-geochemical and hydrogeochemical approaches. The geology of the basin includes sedimentary rock types of sandstone, shale, limestone, alluvium conglomerate and the formations which are composed of sand, silt, clay, laterite and gravel. The geophysical study, which mainly aimed to estimate the depth-to-water table, identification of strata and vadose zone thickness, revealed topsoil, sandy clay, dry porous sandstone, conglomeratic sandstone, limestone and alluvium as the major lithological units in the basin. Geo-electrical curve types revealed an overlying multilayered rock. The vadose zone characterisation, which is the pathway through which contaminants infiltrate, aimed to determine the lithological properties which dictate the travel time of water. This was achieved by determining the hydraulic conductivity of the vadose lithology in the laboratory. Other important parameters such as grain size, porosity, shapes, textural classification and clay types were examined for their attenuation capacity. The hydrogeochemical investigation involving the collection and analysis of water samples from the hand-dug wells and shallow boreholes during the rainy and dry season was aimed at monitoring the groundwater quality of the basin. Ca-Mg-Cl water types and Na-K-Cl water types were delineated. Bacteriological examination of the shallow water reveals the presence of E.Coli, Heterotrophic bacteria and Salmonella/ Shigella. Precipitation which is a component of groundwater recharge ranged between 1 200–1 800 mm from the northern end to the southern end of the basin, respectively. Groundwater level were measured, monitored and average water level were delineated for the formations of the Dahomey Basin. The proposed RTt vulnerability method was applied to evaluate the groundwater vulnerability of the Dahomey Basin. The RTt method is an intrinsic physically based vulnerability method based on the concept of groundwater recharge from rainfall and travel time within the covering lithology over the aquifer. Travel time is the infiltration derived from multiplication of the slope and thickness of the vadose zone divided by fluid velocity. The fluid velocity is derived from the division of hydraulic conductivity by porosity. RTt method application results for the Dahomey Basin were presented on the RTt vulnerability map. The RTt vulnerability map was classified from very low vulnerability (12) to very high vulnerability (100). The RTt vulnerability results for the Dahomey Basin showed 18% of the areas classified as very high vulnerability, 7% of the areas classified as high vulnerability, 64% of the areas classified as moderate vulnerability and 10% of the areas classified as low vulnerability. The compared vulnerability maps of the RTt method and those of the DRASTIC, PI and AVI methods, showed similarities between the RTt method and the AVI and DRASTIC method, respectively. Areas classified as high vulnerability by these methods showed very shallow protective covers, high precipitation and porous aquifer materials, while areas classified as low vulnerability areas include thick protective cover, reduced rainfall, higher slope and higher depth-to-water. The RTt vulnerability map was validated with the hydrochemical tracer using chloride, DO and microbial loads as vulnerability indicators. This study has formulated an RTt method that can be used to predict the vulnerability of shallow unconfined aquifer systems, a key component in groundwater management. The major advantage of the RTt method is the use of less number of parameter to assess groundwater vulnerability. The method has been applied to investigate the regional aquifer of the Dahomey Basin and can be used to predict the aquifer vulnerability of similar basins across Africa with limited data.
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    ItemOpen Access
    A holistic hydrogeological environmental site risk assessment methodology for the fertilizer industry in South Africa
    (University of the Free State, 2013-04) Linde, George Frederik (Ferdie); Vermeulen, Danie
    English: There has been a definitive increase in environmental legislation over the past decade. These new environmental laws established principles such as duty of care and the polluter pay principle. Numerous companies in South Africa have historical impacts, particularly ground water impacts deriving from the period where no or less comprehensive environmental legislation was promulgated. Furthermore, the sudden evolution of environmental legislation has but significant strain on companies to comply with environmental law. The quantification of ground water impact through a methodological approach which can provide adequate information for a decision on the need to disclose the liability as part of the financial audit process is absent in South Africa. This study focussed on deriving a methodology which can be applied in the South African Fertiliser Industry, in assisting with the investigation and quantification of ground water impacts in order to assist with the decision on the need to disclose the liability as part of the financial statements and the newly derived reporting practice of integrated reporting.
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    Quantification and modelling of heterogeneities in aquifers
    (University of the Free State, 2017-01) Ahokpossi, Dehouegnon Pacome; Atangana, Abdon; Vermeulen, Danie
    English: The future of modelling of heterogeneity in aquifers is definitively in the designing of new in situ testing (hydraulic and mass transport) procedures with new corresponding mathematical models. New trends in mathematical differentiation offer opportunity to explore more flexible and practical mathematical model solutions. This applies to both analytical and numerical modelling. Only a sound understanding of rock structures can clearly pose the problem which will then be used to define hydraulic equations to be solved by mathematical models, and numerical software. The most recent concept of differentiation based on the non-local and non-singular kernel called the generalized Mittag-Leffler function, was employed to reshape the model of fractured aquifer fractal flow. The solution was successfully applied to experimental data collected from four different constant discharge tests. Additionally, a new analytical solution to the fractal flow in a dual media was proposed, where the media could be elastic; heterogeneous; and visco-elastic. The existing dual media fractal flow model was modified by replacing the local derivative with the nonlocal operator (operator with Mittag-Leffler kernel, and Mittag-Leffler-Power law kerne)l. The more accurate numerical scheme known as Upwind was used to numerically solve each model. Heterogeneity in a typical South African crystalline rock aquifer was assessed. From this, a methodical level for quantifying and modelling heterogeneity in an aquifer was deduced. It was demonstrated how spatial heterogeneity in aquifers can be modelled based on the most commonly available tools and data in mining environment. The capability of selected numerical geohydrological softwares were assessed using spatial variability of hydraulic parameters (hydraulic conductivity and recharge). Geostatistical tools were specifically applied. Focus was also given to hydro-geochemical characterization by using bivariate scatter plots, Piper and Expanded Durov diagrams, and PHREEQC hydro-geochemical model as complimentary tools to analyse the groundwater chemistry data to describe different hydro-geochemical process which prevail in the monitored groundwater system. Three manuscripts have been submitted out this thesis, in top tier journals of the Natural and Applied Sciences.
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    Surface water - groundwater interactions: development of methodologies suitable for South African conditions
    (University of the Free State, 2013) Moseki, Motlole Christopher; Vermeulen, Danie; Dennis, Ingrid
    Winter (1999) succinctly, made a profound statement to the effect that understanding the basic principles of the interaction between surface water and groundwater is needed for effective management of water resources. Hence, the research investigation was aimed at identifying appropriate methodologies for assessment of surface water ‐ groundwater interaction, thus enhancing the understanding thereof. The methodology used entailed a review of national and international literature on related previous and current models, systems and methods used in assessment and quantification of water exchange between groundwater and surface water. This was then followed by relevant case study analyses where distinct areas where chosen based on availability of relevant data and information by previous investigators. The findings were that various methods and classification systems are widely available but the applicability thereof under the South African conditions depends on the conceptual understanding of the area or system under investigation, availability of data and the basic assumptions associated with the particular model or method. The surface water ‐ groundwater interaction cannot easily be quantified with confidence without requisite data available. The other finding is that use of multiple techniques to reduce uncertainties and to confirm or verify the existence or non‐existence of the interaction is essential. Preferably, at least one method should be utilised to trace flow or qualitatively establish the water exchange while the alternative method is used for quantitative estimation of the interaction between surface water and groundwater. Some of the products emerging from this research investigation include decision tables for choosing applicable analytical method, applicable numerical method and the framework for guiding the selection of appropriate methodologies for assessing or quantifying the interaction between surface water and groundwater. Knowledge generated is applicable to water resource management, resource protection, water allocation and monitoring.
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    Surface water-groundwater interactions: development of methodologies suitable for South African conditions
    (University of the Free State, 2013) Moseki, Motlole Christopher; Vermeulen, Danie; Dennis, Ingrid
    English: Winter (1999) succinctly, made a profound statement to the effect that understanding the basic principles of the interaction between surface water and groundwater is needed for effective management of water resources. Hence, the research investigation was aimed at identifying appropriate methodologies for assessment of surface water - groundwater interaction, thus enhancing the understanding thereof. The methodology used entailed a review of national and international literature on related previous and current models, systems and methods used in assessment and quantification of water exchange between groundwater and surface water. This was then followed by relevant case study analyses where distinct areas where chosen based on availability of relevant data and information by previous investigators. The findings were that various methods and classification systems are widely available but the applicability thereof under the South African conditions depends on the conceptual understanding of the area or system under investigation, availability of data and the basic assumptions associated with the particular model or method. The surface water - groundwater interaction cannot easily be quantified with confidence without requisite data available. The other finding is that use of multiple techniques to reduce uncertainties and to confirm or verify the existence or non-existence of the interaction is essential. Preferably, at least one method should be utilised to trace flow or qualitatively establish the water exchange while the alternative method is used for quantitative estimation of the interaction between surface water and groundwater. Some of the products emerging from this research investigation include decision tables for choosing applicable analytical method, applicable numerical method and the framework for guiding the selection of appropriate methodologies for assessing or quantifying the interaction between surface water and groundwater. Knowledge generated is applicable to water resource management, resource protection, water allocation and monitoring.