Doctoral Degrees (Agricultural Engineering)

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Improved understanding and modelling of hydrological responses in formal and informal urban areas: case study in Tshwane, South Africa.
(2023) Loots, Ione.; Smithers, Jeffrey Colin.; Kjeldsen, Thomas Rodding.
It is widely accepted that urban development results in larger flood peak discharges with faster catchment response times, larger total runoff volumes and lower base flow volumes. However, these effects have not previously been studied in the South African context, where typical development characteristics in both formal and informal settlements differ from those reported in previous studies. In order to configure accurate hydrological models for South African conditions, it is important to understand the impacts of typical South African urban development types on runoff. This study aims to gain new understanding of hydrological processes in the diverse range of South African urban environments and to use this knowledge to develop an improved approach for hydrological modelling in South African urban areas. This study investigates the effects of urban development on runoff, including: (a) total runoff volumes, (b) stormflow volumes, (c) base flow volumes, (d) flood peaks and (e) catchment response time from South African urban catchments, using case studies from Gauteng Province. It is shown that total runoff, stormflow volumes and base flow all increase in the study catchments regardless of whether the upstream development is formal or informal. However, contrary to current scientific consensus, changes in flood peaks and catchment response times with development are statistically insignificant in most catchments with formal urban development in this study. The seeming paradox of increased flood volumes without corresponding increase in flood peaks and decreased catchment response time is attributed to the temporary storage and subsequent attenuation of peaks in these catchments. The catchment with the largest proportion of informal development shows increasing trends in both volume and flood peaks, although catchment response times do not show significant change. It is postulated that the complexity of increased imperviousness without increased connectivity of impervious areas to drainage systems, as typically found in informal settlements, could contribute to this result. In order to assess the impact of the improved understanding and quantification of urban responses on modelling, the Storm Water Management Model (SWMM) was configured for two catchments, first using conventional parameter sets, then incorporating measured and derived imperviousness and connectivity data from this study. The simulation results show that the parameter values proposed in this study improve the results in both catchments. Considerable additional improvement is achieved through the incorporation of pseudo storages to simulate unexpected attenuation in the catchments. Based on the results it is recommended that attenuation be incorporated in hydrological models of urban areas in ungauged catchments with similar characteristics. Recommendations are made for further investigation into reasons for the findings, as well as further studies in other South African urban areas, when additional data is available.
New approaches to the determination of minor frictional losses in irrigation systems.
(2022) Tagwi, Dayton.; Senzanje, Aidan.; Lagerwall, Gareth.
Abstract available in PDF.
Determining an integrated solid waste management action plan for urban Harare city, Zimbabwe: a system dynamics approach.
(2021) Kwenda, Phyllis Rumbidzai.; Lagerwall, Gareth.; Eker, Sibel.; Van Ruijven, Bas.
Abstract available in PDF.
Modelling the infrared assisted hot air drying of beef for biltong production.
(2021) Onyando, Francis Collins Muga.; Workneh, Tilahun Seyoum.; Marenya, Moses Okoth.
Abstract available in PDF.
Development and assessment of regionalised approaches to design flood estimation in South Africa.
(2020) Calitz, Johannes Pieter.; Smithers, Jeffrey Colin.; Kjeldsen, Thomas Rodding.; Gericke, Ockert Jacobus.
Engineers rely on design hydrological information for the design of hydraulic structures, such as dams, bridges, and drainage culverts. No single Design Flood Estimation (DFE) method has been identified internationally as the most appropriate method to use and, in many texts and manuals, the use of a combination of these are recommended. In South Africa, some of the currently recommended and widely used methods were developed outside of South Africa with little or no local adaptation or assessment, and most of the recommended methods were developed prior to 1990. The development of new and updated methods can therefore benefit from the use of much longer observed data sets and new and innovative approaches applied internationally. Four Regional Flood Frequency Analysis (RFFA) approaches widely adopted internationally are direct quantile estimation methods, Probabilistic Rational Method (PRM), Index Flood (IF), and Regional Growth Curve (RGC) methods. The Standard Design Flood (SDF) method is a locally developed PRM. However, the method has been recommended for review in a number of studies, and the IF has been shown to have potential for implementation at a national scale in South Africa. The aim of this study was to develop and assess RFFA approaches for the estimation of design flood quantiles within South Africa utilising the currently available data. This process required the compilation of a hydrological descriptors database, including quality controlled gauged flow data. This data was then utilised to identify a suitable probability distribution for FFA in South Africa, which can be applied at a regional scale through the identification of homogeneous flood producing regions and regional flood models. DFE methods require a range of catchment descriptors to be determined for use in models. Considering the literature reviewed and the available datasets, 17 catchment descriptors were selected for inclusion in the study. The descriptors range from geographic and catchment descriptors to design rainfall quantiles. After data screening, a total of 383 stations were utilised, in the study. The available record lengths and number of gauges were compared to prominent studies undertaken previously and was found to be comparative to the data availability in Australia and the United Kingdom. Linear moments (LM) were adopted for the estimation of the distribution parameters. Five distributions were selected for evaluation based on local recommendations as well as recent international developments: (i) General Extreme Value (GEV), (ii) Generalised Pareto (GPA), (iii) 3-parameter Kappa (KAP3), (iv) Log Pearson Type III (LP3) and (v) Pearson Type III (PE3). The evaluation process relied on an iterative elimination approach, reviewing graphical fits to theoretical distributions, Goodness-of-fit (GoF) criteria, model fit criteria and model uncertainty to identify the most suitable distribution. The graphical fit favoured the GPA, KAP3 and LP3 distributions equally, with the GoF methods ranking LP3 as the most suitable method. Conversely, the GPA was ranked highest for the model fit criterion and displayed the least model uncertainty and is thus recommended as the most suitable distribution for general FFA in South Africa. Two regionalisation approaches were considered to undertake the formation of the pooling groups, i.e. Clustering, and Region of Influence (RoI). For each regionalisation approach the hydrological descriptors were grouped into parameter sets, that constituted all potential descriptor combinations, which were tested for homogeneity as a selection criterion. Using the RoI approach, a maximum of 51% of the regions identified were relatively homogeneous. The super region approach was also applied to identify five dominant regions within which the RoI was applied in an attempt to refine the RoI approach. Using the combination of super regions and RoI provided little additional benefit, increasing the percentage of relatively homogeneous regions identified to only 52.6%. Conversely, the Clustering approach was able to identify 42 relatively homogeneous clusters in South Africa. To assess the suitability of Quantile Regression Technique (QRT) and Parameter Regression Technique (PRT) models in South Africa, four models were developed: (i) a QRT model, (ii) IF with equal station weighting (IF1), (iii) IF with station weighting applied (IF2) and (iv) PRM. Regression models were developed at two scales to estimate the required Scaling Factors, i.e. national and regional, with regional models performing best based on the Nash- Sutcliffe model Efficiency (NSE) coefficient. Six key performance indicators were utilised to assess the quantile estimation of the developed models: (i) NSE, (ii) Relative Error (RE), (iii) Root Mean Square Error (RMSE), (iv) Relative RMSE (RMSEr), (v) BIAS, and (iii) BIASr. The models that performed best in the RE assessment were the IF1 for both regionalisation schemes and the IF2 and PRM models using the RoI. When comparing the BIAS and RMSE of the four best performing clustering and RoI based models, the IF1 and QRT using Clustering models are the dominant models when considering both the RMSEr and the BIASr, the models improved on the results of the remaining models by up to a factor of two. The IF1 and QRT using Clustering models are therefore the best performing models on a national scale. The IF1 however has the added advantage of being able to estimate the entire growth curve as to the predefined QRT models. The IF1 is therefore the recommended model at a national scale, however cognisance needs to be taken when applying the model on the eastern coast due to poor BIASr performance. The new knowledge generated by the study can be divided into data, in the form of potentially the largest database of design flood specific descriptors concentrating on South Africa, and theoretical applications thereof. The theoretical knowledge generated ranges from the investigation into the most suitable frequency distribution to use for FFA in South Africa, to the application of multi-variate regionalisation approaches, which have not been applied in South Africa before. However, one of the key contributions was the development and performance assessment of four DFE models at multiple scales for South Africa for the estimation of peak design flood values.
Moistube Irrigation characterisation and yield response of canola (Brassica napus) under varied Moistube Irrigation.
(2021) Dirwai, Tinashe Lindel.; Senzanje, Aidan.; Mabhaudhi, Tafadzwanashe.
Abstract available in PDF.
Free basic water services standards as indicators to assess inequalities in sustainable access to improved water services.
(2020) Sambo, Doctor Calvin.; Senzanje, Aidan.; Mutanga, Onisimo.
Sustainable access to improved water services is essential to sustain human life and a fundamental human right. Water is used by rural communities for activities that improve their health, wellbeing and livelihoods. As a result, the Sustainable Development Goals (SDG) aim to attain universal access to improved water services provided by Improved Water Sources (IWS). IWS include standpipes in dwellings, communal standpipes and protected dug wells. Aligned to the SDG, the South African government conceived and effected the Free Basic Water Services (FBWS) policy to coordinate efforts to attain universal access to improved water services. However, there have been challenges in implementation of the FBWS policy resulting in a vast proportion of the rural communities without sustainable access to improved water services. The challenges vary from issues related to institutional capacities, accountability and monitoring. A substantial part of the challenge is the lack of reliable data to inform decision-makers involved in the planning and management of improved water services in the rural communities. The challenge is worsened by the indicator used to monitor water access as it only considers the proportion of the population provided with an IWS. This indicator does not track the sustainability aspects of the level of water services provided by IWS over their useful life. The research sought to address the gaps that exists with regards to making available the information required to inform decision-makers involved in the planning and management of improved water services, and the use of indictors to measure sustainability aspects of water services provided. The aim of the research was to assess inequalities in access to improved water services using a set of indicators derived from the FBWS standards, and investigate and analyse the complex interactions of the factors that influence access to improved water services in Makhudutamaga Local Municipality (MLM), Limpopo Province, South Africa. Stratified random sampling was employed to determine representative samples of the settlements (39) and households (396) in the study area. Survey questionnaires were administrated to collect qualitative data on households’ satisfaction with FBWS policy and water services provided as well as to collect qualitative and quantitative data on the level of water services provided based on distance, quantity, reliability, flow rate, water quality, and cost. Transect walks were employed to collect supporting information to enhance an understanding of the local context. Furthermore, key informant interviews combine with complex systems approach (e.g. network) were employed to collect qualitative data and analyse the complex interactions of factors that influenced sustainable access to improved water services. The results indicated that between 69.7% - 95.0% of households were satisfied with aspects of the FBWS standards. When using the standards to assess households’ satisfaction with improved water services provided, most of the households were satisfied with distance (62.0%), quantity (61.2%), flow rate (52.7%), and water quality (54.8%), but unsatisfied with the reliability (56.3%) and cost of buying water (58.0%). An assessment of the level of water services provided indicated that aspects (e.g. reliability and cost) of the improved water services provided did not comply with the FBWS standards. The results also indicated that there were statistical differences in access to improved water services across the 4 water schemes for distance [H(3) = 61.33, p = 0.00], quality [H(3) = 72.83, p = 0.00, flow rate [H(3) = 20.12, p = 0.00], and quality [H(3) = 17.21, p = 0.00] no difference for reliability [H(3) = 1.37, p = 0.712]. The majority of households (78.5%) could not afford the cost of buying water. An investigation of the factors that influence sustainable access to improved water services found that limited budget, limited/no water supply and improper operation and maintenance (O&M) were critical factors that influenced sustainable access to improved water services. Therefore, the proposed targeted interventions included increased budget, improved institutional capacity and improved monitoring. It was concluded that there are inequalities in sustainable access to improved water services provided based on FBWS standards. The inequalities are as a result of the complex interactions of categories of factors that influence sustainable access to water services. This study provides an informational advantage in understanding why the situation is as it is on the ground to contribute to evidence-based strategic planning and management of improved water services to ensuring sustained water access in rural municipalities. It is a recommendation of this study for the proposed targeted interventions to be piloted and adopted if found to be suitable to address identified challenges in the study area. The proposed interventions include but not limited to a review of the funding model to respond to the situation on the ground-based on monitoring information, and develop and implement a reasonable participatory water rationing strategy.
Life cycle assessment and the productivity study of the sugar industry in Sudan.
(2020) Ibrahim, Tageldeen Saeed.; Workneh, Tilahun Seyoum.
Abstract available in PDF.
Development of a solar powered indirect air cooling combined with direct evaporative cooling system for storage of fruits and vegetables in Sub-Saharan Africa.
(2019) Sibanda, Sipho.; Workneh, Tilahun Seyoum.
Abstract available in PDF.
The development of the Water-Energy-Food Nexus Index and its application to the Southern African Development Community.
(2020) Simpson, Gareth Beresford.; Jewitt, Graham Paul Wyndham.
This thesis commences with a review of the development and relevance of the water-energy-food (WEF) nexus as a framework for achieving resource security. Based on academic and grey literature it includes an assessment of what the WEF nexus is, a review of its novelty (or lack thereof), and describes the challenges associated with integrating and optimising the WEF nexus. The criticism that several WEF nexus conceptualisations neglect distributional justice is considered, followed by a reflection on governance aspects associated with the approach. Four short WEF nexus case studies illustrate nexus considerations. The research subsequently assesses the status quo of opinion within the WEF nexus fraternity. The approach is not yet a decade old, and several practitioners have called for a shift in focus from ‘nexus thinking’ to ‘nexus doing.’ Various research tools to support nexus action are presented. Next, a comprehensive WEF nexus case study that includes indicators and GIS-base maps is offered. The case study is the Mpumalanga Province in South Africa, which represents a melting pot for the WEF nexus. Within this province is a strategic water area, extensive coal mining for energy generation and a considerable portion of the nation’s high potential agricultural land. This nexus assessment yields a radar chart that represents a visualisation of six water-, energy- and food-related indicators. An anthropogenic WEF nexus framework is subsequently motivated and presented. This framework has been utilised to develop the core output of this research project, namely, the development of a country-level composite indicator that has been established for 170 nations. Following an assessment of 87 globally applicable water-, energy- and food-related indicators, 21 were selected to constitute the WEF Nexus Index. This index provides a quantitative perspective of this multi-centric lens for evaluating trade-offs necessary to achieve sustainable development. To this end, it can be utilised for assessing national progress relating to integrated resource management as well as supporting decision making and policy development. The relevance and usefulness of the outcomes are demonstrated through a detailed discourse of the findings for selected regions and countries. An extended analysis is provided for the Southern African Development Community (SADC). WEF nexus assessments in the decade leading up to the 2030 Sustainable Development Goal (SDG) target year must be more comprehensive. Qualitative studies must be conducted in parallel with quantitative assessments. There is no one-size-fits-all method for integrated resource management utilising the WEF nexus. Instead, the approach must be tailored for each unique situation, and the WEF Nexus Index can be a catalyst and entry-point for such studies. By evaluating a subset of the SDGs, the index is complementary to the SDGs. The WEF Nexus Index is not a silver bullet that will solve all the significant development or environmental challenges facing humanity. This approach can, however, be added to the sustainability toolbox that is being utilised to engineer ‘the future we want’.
Kick-starting aquaponics production in South Africa.
(2018) Mchunu, Ntobeko.; Lagerwall, Gareth.; Senzanje, Aidan.
Abstract available in PDF.
Development of updated design norms for soil and water conservation structures in the sugar industry of South Africa.
(2020) Otim, Daniel.; Smithers, Jeffrey Colin.
Sugarcane in South Africa is grown on wide-ranging soils, sometimes in non-ideal climates and on steep topographies where soils are vulnerable to erosion. A consequence of unsustainable soil loss is reduction in field production capacity. Sugarcane fields are protected against erosion through, inter alia, the use of engineered contour banks, waterways and spill-over roads. A comparison of design norms in the National Soil Conservation Manual and norms used in the sugar industry clearly shows discrepancies (e.g. maximum slope and cover factor of sugarcane) that need to be investigated. Furthermore, the sugar industry design nomograph was developed based on an unsustainable soil loss limit, does not include any regional variations of climate and the impact on soil erosion and runoff and does not include vulnerability during break cropping. The aim of this research was to develop updated design norms for soil and water conservation structures in the sugar industry of South Africa. Many soil loss models exist, of which empirical models are the most robust and provide stable performances. The Modified Universal Soil Loss Equation (MUSLE) which is embedded in the Agricultural Catchments Research Unit (ACRU) model, estimates event-based soil erosion and, given that the majority of soil erosion occurs during a few extreme events annually, the design norms were updated using the MUSLE. The ACRU model is a daily time step, physical- conceptual agrohydrological model. Runoff volume, peak discharge and sediment yield were simulated with the ACRU model and verified against the respective observed data. The results showed good correlations and the ACRU model can be confidently applied in the development of updated design norms for soil and water conservation structures in the sugar industry of South Africa. The ACRU model was used to conduct simulations for the different practices in the sugar industry and the results used to build the updated tool for the design of soil and water conservation structures in the sugar industry of South Africa, using MS Access with a background database and a graphical user interface. The updated tool is robust, based on sustainable soil loss limits, includes regional variations of climate and their impact on soil erosion and runoff and also includes vulnerability during break cropping. It is more representative of conditions in the sugar industry of South Africa and therefore recommended for use in place of the current sugar industry design norms. The results also indicate that soil and water conservation structures result in insignificant reductions in stream flow and would not likely necessitate their declaration as Stream Flow Reduction (SFR) activities as contained in the National Water Act of South Africa. Consequently, a 20 year return period is recommended for the design of soil and water conservation structures and the cost implication of varying design return periods from the minimum 10 year return period to the 20 year return period ranges from 16% to 35% across the four homogenous regions in the sugar industry of South Africa.
Flood disaster preparedness and impacts on rural households: a comparative study of Mwandi District of Zambia and Eastern Zambezi Region of Namibia.
(2019) Mabuku, Monde Patrina.; Senzanje, Aidan.; Mudhara, Maxwell.; Jewitt, Graham Paul Wyndham.; Mulwafu, Wapulumuka O.
The Zambezi Basin is considered vulnerable to climate variability as evidenced by the recurrent floods. The increased occurrence and severity of floods in recent years in areas previously not flooded has inundated parts of Eastern Zambezi Region of Namibia and Mwandi District of Zambia. The magnitude and frequency of these floods, coupled with poor disaster preparedness and lack of effective adaptation strategies, is believed to have negative impacts on rural households. Therefore, a cross country case study was carried out in order to assess the impacts of floods on income, crop production and livestock ownership; to determine the level of flood disaster preparedness; to assess coping and adaptation strategies undertaken by the rural households, and to develop a Household Flood Disaster Resilience Framework (HFDRF). Furthermore, the factors influencing the choice of different adaptation strategies and preparedness level were determined. Data were collected through structured and semi- structured questionnaire survey, focus group discussions, literature reviews and observations. The results indicated that floods had statistically significant impacts on income, crop production and livestock ownership of flooded rural households in both Namibia and Zambia. Rural households depended on both short-term coping and long-term adaptation strategies in order to minimize the negative impacts of floods and flood disasters. Households coped with floods through charcoal production, sale of firewood, sale of grass and reeds, collection of wild food and receipt of food aid. Long-term adaptation strategies included planting trees, fish farming, and flood water harvesting, temporary relocation to higher ground, and changing planting dates, among others. A majority of the households were well prepared (52%) for flood hazards in Namibia, whilst a minority were well prepared (9%) in Zambia. Furthermore, flood preparedness was influenced by sense of community, risk perception, self-efficacy, responsibility efficacy, outcome expectancy, education level, marital status, access and size of land. The study concludes that a variety of factors influence level of flood preparedness and adaptation strategy choices. For policy purposes, this suggests that relevant stakeholders’ interventions should consider these factors in order to enhance the rural households’ adaptive capacity to flooding. Furthermore, results on the impacts of floods on rural households could help in targeting the most vulnerable households in responding effectively to food disasters. This study informs decision makers and practitioners who aim to strengthen disaster risk reduction and management in the two countries and under similar environments, on the status quo of flood impacts, adaptation, and preparedness. The Household Flood Disaster Resilience Framework can be used as a tool for monitoring rural households’ flood resilience.
Characterization of flour and starch from Zambian cassava cultivars and application in frozen wheat bread dough.
(2019) Chisenga, Shadrack Mubanga.; Workneh, Tilahun Seyoum.; Bultosa, Geremew.
Abstract available in pdf.
Object-orientation and integration for modelling water resource systems using the ACRU model.
(2018) Clark, David John.; Smithers, Jeffrey Colin.; Jewitt, Graham Paul Wyndham.
Water is a limiting resource in South Africa, with demand in many catchments exceeding supply, necessitating transfers of water between catchments. This situation requires detailed and integrated management of the country’s water resources, considering environmental, social and economic aspects as outlined in the National Water Act (Act 36 of 1998). Integrated water resources management (IWRM) will require better data and information through monitoring and integrated water resources modelling. The ACRU hydrological model is an important repository of South African water research and knowledge. In recent years there have been technological advances in computer programming techniques and model integration. The thesis for this study was that the valuable knowledge already existing in the ACRU model could be leveraged to provide a better hydrological model to support IWRM in South Africa by: (i) restructuring the model using object-oriented design and programming techniques, and (ii) implementing a model interface standard. Object-oriented restructuring of the ACRU model resulted in a more flexible model enabling better representation of complex water resource systems. The restructuring also resulted in a more extensible model to facilitate the inclusion of new modules and improved data handling. A new model input structure was developed using Extensible Markup Language (XML) to complement the object-oriented structure of the ACRU model. It was recognised that different models have different purposes and strengths. The OpenMI 2.0 model interface standard was implemented for ACRU, enabling ntegration with other OpenMI 2.0 compliant specialised models representing different domains to provide a more holistic IWRM view of water resource systems. Model integration using OpenMI was demonstrated by linking ACRU to the eWater Source river network model. A case study in the upper uMngeni Catchment in South Africa demonstrated: (i) the benefits of the object-oriented design of the restructured ACRU model, in the context of using ACRU to create modelled catchment-scale water resource accounts, and (ii) the integration of ACRU with another model using OpenMI. The case study also demonstrated that despite the improvements to the ACRU model, the simulations are only as good as the model input data.
Variations in growth yield and metabolities of African ginger (Siphonochilus Aethiopicus) in response to irrigation regimes and nitrogen levels.
(2017) Salimina, Mokgehle Ngoakoana.; Tasfay, Samson Zeray.; Araya, Hintsa Tesfamicael.
Medicinal plants are valuable natural resources used as traditional medicine and have economic significance. African ginger (S. aethiopicus) (Schweinf.) B.L. Burtt is one of the most important rhizomatous plants, highly-valued for its medicinal properties and wide distribution in many regions of southern Africa. The plant is currently listed on the Red List of South African endangered species due to overharvesting. The increased demand for plant material has led to extinction in other areas of South Africa. The loss of wild populations harvested will destroy the natural habitats and genetic diversity in the long term. The demand for S. aethiopicus plant parts, particularly the rhizome is associated with the medicinal remedies possessed by the plant. The rhizomes have been traditionally used for the treatment of coughs, colds, asthma, headaches, pain, inflammation and malaria. Currently, there is limited scientific evidence on the cultivation and response of secondary metabolites of S. aethiopicus to agronomic practices. Cultivation of medicinal plants is a good approach to conserve species biodiversity and meet current demands for plant based products. This study investigated the variations in growth, yield and metabolites of S. aethiopicus in response to cultivation practices for commercial production and further development of medicinal products. In this study, total phenolic content, flavonoid content and antioxidant activity of S. aethiopicus leaf, rhizome and root from varying areas (Mpumalanga, KwaZulu-Natal, Limpopo and North West) were evaluated. Total phenolic and flavonoid contents were investigated by Folin-Ciocalteu and aluminium chloride (AlCl3) colorimetric methods, respectively. Antioxidant activity in different parts of S. aethiopicus was evaluated by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and ferric reducing power (FRAP). Furthermore, the study determined the variations in soluble sugars in the leaf, rhizome and root as influenced by varying growing areas. The results showed high concentration of sucrose, glucose and fructose in the leaf and root as influenced by different growing areas. A higher content of both total phenolics and flavonoids were found in the root from Mpumalanga (54.5±2.0 mg GAE/g and 14.83±0.06 µg QE/g, respectively) compared to the leaf and rhizome from other growing areas. KwaZulu Natal also exhibited high flavonoids in the leaf (12.72±1.18 µg QE/g), rhizome (14.21±1.98 µg QE/g) and root (12.88±0.57 µg QE/g) compared to other growing areas. In both methods, the leaf exhibited higher antioxidant activity than the root and rhizome. The high antioxidant activities exhibited in the leaf from Mpumalanga suggest its adaptive capabilities to different environments. S. aethiopicus parts could be used as a potential source for antioxidant properties and encourage cultivation under different growing areas to conserve its biodiversity and increase species populations. The effect of nitrogen levels and irrigation regimes on biomass yield, stomatal conductance, chlorophyll content and leaf area index was investigated under the rainshelter for two growing seasons. The results of this study conclusively reveal that the plant height and number of leaves per plant were significantly higher towards maturity. Plants grown with 50 and 100 kg N/ha had greater plant height, number of leaves per plant, LAI, SPAD values and biomass yield that eventually resulted in higher dry matter production. Stomatal conductance was higher throughout the growing period and decline in response water stressed treatment. The high amount of water utilized from well watered treatment (30% ADL) compared to moderate (50% ADL) and severe (70% ADL) treatments could be attributed to improved water availability and superior plant canopies. Further experiments should be conducted to evaluate different xvi combinations of agronomic practices to fully exploit the growth of S. aethiopicus under different conditions. The high amount of water utilized from the well watered treatment (30% ADL) compared to moderate (50% ADL) and severe (70% ADL) treatments could be attributed to improved water availability and superior plant canopies. The well watered treatment (30% ADL) had a significantly higher total biomass, fresh and dry rhizome yield compared to other water stressed treatments. The response of water stress and nitrogen levels showed significant accumulation of plant flavonoids and phenolics in leaf, rhizome and root. In plant carbohydrates, root had high sucrose content with the application of low N under severely stressed (70% ADL) treatment. The investigation of volatile components of leaf, rhizome and root in response to irrigation regimes and nitrogen levels were analysed by GC-MS. The results showed that the highest volatile components in the root and rhizome were terpenes, as compared to the increased components of aliphatic acids, benzenoids and aliphatic aldehydes in the leaf. In all treatments and parts, the odorant sesquiterpene (1E)-5-Methyl-1-(2, 6, 6-trimethyl-2, 4-cyclohexadien-1-yl)-1, 4-hexadien-3-one was the most abundant volatile compound. The 4-Hydroxy-4-methyl-2-pentanone was detected under severely stressed (70% ADL) treatment with the application of 100 kg N/ha. Severely stressed (70% ADL) treatment with minimal application of N induced the terpenes components in all plant parts. The study showed that volatile components of S. aethiopicus vary with plant sources, water stress and mineral nutrient deficiency. Knowledge on the impact of S. aethiopicus parts will provide a useful guide for selection towards identifying profiles of volatile compounds and explore the additional bioactive compounds for therapeutic use. Taken together, this study represents the importance of cultivation methods as an alternative approach to wild harvesting, conserving S. aethiopicus for commercial production and exposure to water stress conditions for high secondary metabolites.
Computational and numerical analysis of differential equations using spectral based collocation method.
(2019) Samuel, Mutua.; Motsa, Sandile Sydney.
In this thesis, we develop accurate and computationally eﬃcient spectral collocation-based methods, both modiﬁed and new, and apply them to solve diﬀerential equations. Spectral collocation-based methods are the most commonly used methods for approximating smooth solutions of diﬀerential equations deﬁned over simple geometries. Procedurally, these methods entail transforming the gov erning diﬀerential equation(s) into a system of linear algebraic equations that can be solved directly. Owing to the complexity of expanding the numerical algorithms to higher dimensions, as reported in the literature, researchers often transform their models to reduce the number of variables or narrow them down to problems with fewer dimensions. Such a process is accomplished by making a series of assumptions that limit the scope of the study. To address this deﬁciency, the present study explores the development of numerical algorithms for solving ordinary and partial diﬀerential equations deﬁned over simple geometries. The solutions of the diﬀerential equations considered are approximated using interpolating polynomials that satisfy the given diﬀerential equation at se lected distinct collocation points preferably the Chebyshev-Gauss-Lobatto points. The size of the computational domain is particularly emphasized as it plays a key role in determining the number of grid points that are used; a feature that dictates the accuracy and the computational expense of the spectral method. To solve diﬀerential equations deﬁned on large computational domains much eﬀort is devoted to the development and application of new multidomain approaches, based on decomposing large spatial domain(s) into a sequence of overlapping subintervals and a large time interval into equal non-overlapping subintervals. The rigorous analysis of the numerical results con ﬁrms the superiority of these multiple domain techniques in terms of accuracy and computational eﬃciency over the single domain approach when applied to problems deﬁned over large domains. The structure of the thesis indicates a smooth sequence of constructing spectral collocation method algorithms for problems across diﬀerent dimensions. The process of switching between dimensions is explained by presenting the work in chronological order from a simple one-dimensional problem to more complex higher-dimensional problems. The preliminary chapter explores solutions of or dinary diﬀerential equations. Subsequent chapters then build on solutions to partial diﬀerential i equations in order of increasing computational complexity. The transition between intermediate dimensions is demonstrated and reinforced while highlighting the computational complexities in volved. Discussions of the numerical methods terminate with development and application of a new method namely; the trivariate spectral collocation method for solving two-dimensional initial boundary value problems. Finally, the new error bound theorems on polynomial interpolation are presented with rigorous proofs in each chapter to benchmark the adoption of the diﬀerent numerical algorithms. The numerical results of the study conﬁrm that incorporating domain decomposition techniques in spectral collocation methods work eﬀectively for all dimensions, as we report highly accurate results obtained in a computationally eﬃcient manner for problems deﬁned on large do mains. The ﬁndings of this study thus lay a solid foundation to overcome major challenges that numerical analysts might encounter.
Modelling of micro-environment inside evaporatively and coolbot cooled stores using computational fluid dynamics models and changes in quality of stored tomatoes.
(2018) Tolesa, Getachew Neme.; Workneh, Tilahun Seyoum.
The postharvest loss of fresh produce is a global problem, with the tomato fruit being subjected to a 30-50% loss of total production after harvest. The cost and the technicality of modern technology, including mechanical refrigeration, are not appropriate and sustainable for small-scale and middle-income fruit and vegetable farmers. Low-cost cooling technologies, such as evaporative cooling (EC), CoolBot-air-conditioning (CBAC) and a combination of the two (EC+CBAC), provide alternative solutions to minimize postharvest losses. However, there is insufficient information on the modelling of airflow, heat and mass transfer, using the computational fluid dynamics (CFD). The aims of this study were: i) to investigate the real-time airflow pattern, temperature, enthalpy, heat flux and relative humidity distribution inside the unloaded evaporative cooler and CoolBot-air-conditioner cooling systems, using CFD modelling techniques, ii) to evaluate the effect of inlet air characteristics on the airflow resistance inside the selected appropriate semi- and fully-loaded cold storage chambers, iii) to screen the best combinations of pre-storage disinfection treatments, combined with the low-cost cooling technologies, in terms of changes in quality of tomato fruit, and iv) to develop predictive models for the estimation of changes in quality and probability of marketability, using experimental data, obtained during the storage of tomatoes, after they have been subjected to different postharvest treatments and low-cost cooling technologies. The specific aim of this study was to investigate the real-time airflow pattern, temperature and heat flux inside EC, CBAC and EC+CBAC storage systems, using CFD models, to evaluate the changes in the quality of stored tomatoes and to develop predictive models for quality changes of tomatoes stored under EC and CBAC. The experimental results showed that the indirect heat exchanger (IHE) and one evaporative cooling wet pad were sufficient to reduce the temperature of the hot ambient air from 34.1℃ to 22.82℃. However, using multi-layer evaporative cooling pads was proven to have significant importance in increasing the relative humidity of air leading to the storage chamber. The EC+CBAC combination was the best for maintaining an optimum temperature (8-15°C) and relative humidity (80-99%) of the micro-environment inside the cold storage chamber during the storage period. A computational fluid dynamics (CFD) model was used to investigate the airflow, temperature and heat flux across the IHE and psychrometric unit. The numerical results showed that the psychrometric unit was not sufficient for reducing the ambient air temperature to at least near the wet-bulb temperature of the ambient air, hence, the modification of the airflow regulating fan is required. The steady state and transient CFD modelling of the micro-environment was performed in order to visualize the inside of the unloaded EC, CBAC and EC+CBAC storage chambers, the non-uniform distribution of air velocities, temperature and heat flux was found inside the storage chambers. Visual observations of velocity vector magnitude and temperature uniformity distribution inside unloaded stores were demonstrated in decreasing order, from EC+CBAC, CBAC and EC, respectively. The modelling of the semi- and fully-loaded tomatoes stacked in the EC+CBAC cold storage chamber, using CFD models, was found to be crucial for determining the airflow resistance, which is the fundamental parameter for the engineering analysis of heat and mass transfer inside the cold storage chamber during the re-design process. The results showed that the long-side of the tomato stack, facing the direction of the airflow, had a lower airflow resistance, when compared to the short-side stack. Therefore, it was demonstrated that there was better airflow through the long-side stack. The CFD models that were developed were validated by comparing the air velocity and the reported RMSE was found to be acceptable, compared to literature. The information generated in this study has resulted in EC and CBAC cold store systems being used, for the first time, for the analysis of airflow characterisation and heat transfer that takes place inside a storage chamber. The integrated approach, combining the application of low-cost evaporative cooling storage and pre-storage disinfection treatments (i.e. chlorinated water and anolyte water), was found to be the best method, for extending the shelf-life of the tomato fruit, by maintaining the better quality of fresh tomatoes for 28 days of storage. A combination of the green maturity stage and both chlorinated and anolyte water maintained better quality parameters, in terms of the colour, firmness and many other quality indices, when using the low-cost cooling technology during storage period. Logistic regression, polynomial, fractional polynomial, multivariate and covariance models were developed for low-cost cold storage systems for the first time, to predict the quality of the stored tomatoes under integrated postharvest handling and treatment. These models were developed for the tomato quality indices subjected to low-cost cooling technologies and pre-storage disinfection treatments and they were found to follow curvilinear relationships. Utilizing the logistic regression model, the marketability of tomatoes was found to be higher for tomatoes stored under an evaporative cooling environment than for those stored under ambient environment. The fractional polynomial, polynomial and multivariate models that were developed can be used by farmers to predict the changes in the quality of fresh tomatoes during storage, for the selective quality parameters such as tomato firmness, colour and many others. A study of model’s development, as well as the use of low-cost cooling technologies and pre-storage disinfection treatments, should be conducted for other fresh produce.
Value chain analysis and determinants of production and consumption of African leafy vegetables in Limpopo Province of South Africa.
(2018) Senyolo, Granny Mmatsatsi.; Zegeye, Edilegnaw Wale.
There has been a decline in the production, utilization and diversity of African leafy vegetables (ALVs) such as cowpea leaves, pumpkin leaves, amaranth, collard greens, mustard greens, etc., which poses a threat to the status of food security and development in the sub-Saharan region. Research has shown that ALVs have high market potential and contribute substantially to household incomes, food security, health and nutrition. However, the scientific and donor communities often give less attention to research on, and development of, these crops. This study focuses on the commercial production of ALVs, a relatively new economic activity, in the Limpopo Province of South Africa that may assist rural, small-scale farmers to diversify, improving their economic independence and livelihoods. In attempting to provide an impetus to the ALV industry, the South African government currently offers free training in ALV production, extension services, free high quality seed, free fertilizers and pesticides. Considering the geographical suitability and the magnitude of investment made towards the ALV development programme, there is a need to understand consumer behaviour towards ALVs, and why many farmers are not participating in the industry. There has also been limited research so far on the challenges and opportunities in producing, value adding, and marketing of ALVs in South Africa. This study is, therefore, an attempt to address these knowledge gaps. It also provides an opportunity to draw relevant policy and management implications to inform future strategies in the industry. Given this background, the specific objectives of the study were to: (i) analyse the value chain of ALVs in Limpopo Province; (ii) examine the factors influencing households’ participation decision in the production of ALVs in Limpopo Province; (iii) determine the factors influencing consumers’ purchasing decisions and expenditure levels for ALVs; and (iv) determine socioeconomic and perception factors affecting willingness-to-pay. To analyse the value chain of ALVs in the Limpopo Province of South Africa, prominent value chain actors, institutions governing the chain, infrastructural endowments, key factors and challenges affecting the success or failure of the value chains, were identified. Relationships among the value chain actors were weak, with transactions based primarily on spot markets. While smallholder farmers producing ALVs attain high gross margins, their intention to participate in mainstream markets is impeded by lack of technical knowledge of production, lack of packaging and processing services, poor infrastructure, deficient contractual agreements vi between actors, and lack of access to finance. Although producers currently attain relatively high gross margins, more benefits might be realized if government services (such as training, seed production and distribution) could either be decentralized or privatized. Future policy interventions should focus on promoting value addition along the ALV chain, including the provision of cold storage facilities by municipalities closer to smallholder farmers in the rural areas to stabilize farm gate prices to encourage continuation of production. A double-hurdle model that accounts for whether or not smallholder farmers produce ALVs (decision to participate) and how much land was allocated for ALV production (level of participation) was used to examine the factors influencing households’ participation decision in the production of ALVs in the Limpopo Province. Participation and level of participation decisions were analysed using cross-sectional data collected from 126 smallholder farmers in 2013. The empirical results suggest that factors explaining participation decision and level of participation are different. Hence, it is imperative that policies that are aimed at incentivising both participation and level of participation and their impacts on food security and nutrition target different groups of people. Furthermore, the commercialisation of ALVs could also promote rural development in the study area. Factors influencing consumers’ decisions to purchase ALVs in the Limpopo Province were also examined using the double-hurdle model as it accounts for whether or not consumers purchase ALVs and how much they spend on these vegetables. The decision to purchase and the level of expenditure were analysed using cross-sectional data collected from 299 urban and rural households during 2012. The results show that perception factors (such as nutrition) and some socio-economic factors (such as gender, education, marriage and urbanization) influence only purchasing decisions, while other factors such as age and distance to the market influence only the level of expenditure on ALVs. In addition, other perception (perception that ALVs are a relish, tasty and affordable) and socio-economic (dependency on social grants) factors influenced both the purchasing decision and the level of expenditure. Interventions that promote value addition of ALVs through sorting, packaging and processing by commercial processors that reduces pre-cooking preparation time and increases storage can encourage young, male, urban and educated consumers to purchase ALVs. Furthermore, awareness-raising programmes about the nutrition and health benefits of ALVs on media (such as local and national radio and television stations and social media in locally understood languages), might promote the consumption of ALVs by educated and urban households. vii Socio-economic and perception factors influencing willingness-to-pay (WTP) for ALVs were also determined. Cross-sectional data were collected from 299 randomly selected households using a contingent valuation questionnaire. The descriptive results revealed that almost 80 percent of respondents would be willing to pay a premium for ALVs. An Ordered Probit model was applied for identification of households’ socioeconomic and perception factors that influence WTP. WTP was found to be mainly a function of socio-economic factors, namely gender, urbanization, age, distance to the market, tastes/preferences and availability of ALVs throughout the year. Smallholder farmers of ALVs, plant breeders, marketers and policy makers are encouraged to develop efficient production and marketing strategies. This, in turn, provides a means of improving food security and livelihoods, especially in support of the poor, rural, smallholder farmers. The study recommends the empowerment of smallholder households and the youth with productive resources such as extension services, technical support and a more secure land tenure system to improve their livelihoods. The commercialisation of ALVs could promote rural development in the study area, as ALVs are indigenous to Limpopo. Understanding the nature of these constraints and how they can possibly be alleviated is very important from a policy perspective, as this process will inform the formulation of improved market access strategies. The study also recommends a strategic awareness campaign to influence the behaviour of producers and consumers and nutrition education to increase knowledge and awareness of the nutritional value of ALVs. Further recommendations are also made towards institutionalising and strengthening collective marketing under different options, which reflect producers’ socioeconomic status and the prevailing institutional and policy environment in Limpopo Province.
Vachellia sieberiana var. woodii a high-altitude encroacher: the effect of fire, frost, simulated grazing and altitude.
(2018) Russel, Jennifer Mary.; Tedder, Michelle Jennifer.
ABSTRACT There is increasing evidence that savannas and grasslands throughout the world are experiencing bush encroachment. The replacement of grassy biomes with woody biomes has serious consequences for net primary productivity. The grasslands of South Africa are not exempt from this phenomenon. Despite this, the drivers of the tree:grass dynamics are still robustly debated. In mesic and moist savannas and grasslands, the tree:grass balance appears to be maintained mainly through disturbance such as fire, frost and herbivory or a combination of disturbances. Other factors such as competition for resources may play a modifying role. High altitude grasslands are frequently within a climatic zone that would support trees, yet trees are absent. The answer as to what mechanism excludes trees from these grassy biomes continues to elude researchers. Very often low temperature is cited as a possible mechanism. Vachellia sieberiana var. woodii is a typical savanna tree which is absent from high altitudes. However, it has been encroaching into the grasslands along the escarpment of the Drakensberg, KwaZuluNatal, South Africa, over several decades, although is still excluded from the top of the escarpment. I acquired aerial photographs and satellite images covering the Van Reenen’s Pass area, north-western KwaZulu-Natal, dating from 1955 to 2015. These images confirmed that V. sieberiana was increasing in density along the escarpment, but that no V. sieberiana was present on top of the escarpment, despite the successful establishment of other tree species. The photographs and images also suggested that V. sieberiana was extending its range into higher altitudes. Because fire, frost and herbivory are generally thought to be the determinants of the structure of grasslands and savannas, I conducted field trials along the altitudinal gradient on Van Reenen’s Pass, investigating the effect of these determinants on the establishment of transplanted V. sieberiana saplings at three different altitudes. Competition for resources were briefly taken into consideration, although they were not the main thrust of the project: soil nutrients and root gaps. Soil moisture was not a concern as the area is what is defined as mesic. The transplanted saplings were smallest at the high-altitude site and largest at the low-altitude site after two growing seasons in the field. The response of the saplings to the various treatments was not consistent at the three sites. There was no response to the treatments at the highaltitude site; a significant response to fire, frost and simulated grazing at the mid-altitude sites; and a significant response to frost and simulated grazing at the low-altitude site.

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