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Masters Degrees (Environmental Hydrology)

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    The evaluation and quantification of the drought propagation process using satellite earth observation products.
    (2022) Sukhdeo, Trisha.; Chetty, Kershani Tinisha.; Gokool, Shaeden.
    Droughts can be categorized in four types namely, meteorological, agricultural, hydrological and socio-economic drought. Droughts have the potential to occur either as an isolated event, mutually exclusive event or through the progression from one form to another. The use of drought indices were recognized as an approach capable evaluating and monitoring the characteristics of the different drought types. The aim of this study is to evaluate and quantify drought characteristics as it evolves and propagates form meteorological to agricultural drought, within two climatically different regions within South Africa, namely the uMngeni Catchment and the Breede-Overberg Catchment. These areas generally have insufficient networks of ground-based observations to provide continuous and long-term data. Therefore, Satellite Earth Observation (SEO) data and Google Earth Engine (GEE) were utilized. The Standardized Precipitation Index (SPI) was selected to quantify meteorological drought, whilst the Standardized Precipitation Evapotranspiration Index (SPEI) and Vegetation Health Index (VHI) was chosen to assess agricultural drought at both of the selected sites. The methodology undertaken firstly involved validating the SEO data against in-situ data. Thereafter, historical droughts were calculated by the SPI and SPEI indices at various timescales. Assessments were then conducted to determine the applicability of satellite based drought index VHI on quantifying agricultural drought conditions. The final assessment involved conducting propagation analysis between the drought indices. The findings of this study indicated that SEO have the potential to be utilized in the collection and monitoring of drought conditions. VHI was recognized to be scale dependent index, especially when considering averaging values. The findings of this study further suggested that the uMngeni region was more susceptible to the impacts associated with meteorological droughts characteristics whilst the Breede-Overberg region was more susceptible to the impacts associated with agricultural drought characteristics. Understanding the impacts and characteristics associated with the drought propagation process may further provide theoretical knowledge that can be used to facilitate more informed disaster, water and agricultural management and mitigation strategies to be implemented. If decision makers were to only consider drought using meteorological assessments for management decisions, the resulting strategies produced may be misleading as the impacts of an agricultural drought event may still be persistent.
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    An assessment of the use of remote sensing to estimate catchment rainfall for use in hydrological modelling and design flood estimation.
    (2022) Khakhu, Khodani.; Smithers, Jeffrey Colin.
    The accurate estimation of catchment rainfall is crucial, especially in hydrological modelling and flood hydrology which is used for the planning and design of hydrological infrastructures such as dams and bridges. Traditionally, catchment rainfall is estimated by making use of ground-based point rainfall measurements from rain gauges. The literature review conducted in this study supports that there is evidence of a decrease in the number of operational groundbased rainfall stations in South Africa which presents a challenge when estimating catchment rainfall for use in hydrological modelling and design flood estimation. Thus, innovative ways are required to estimate catchment rainfall and to improve the estimation of catchment design rainfall. This study investigated the use of remote sensing as an alternative way to estimate catchment design rainfall. To do this, a pilot study was first used to develop and test the methodology using a quaternary catchment that was selected based on the raingauge density. This was followed by the application of a refined methodology in another quaternary catchment which was used to verify the results that were obtained in the pilot study. After a comprehensive review of the literature, the remote sensing product selected for this study was the CHIRPS rainfall product. The methodology adopted first validated the remotely sensed rainfall data using the observed rainfall data and the estimated remotely sensed rainfall values were bias corrected using the observed rainfall data. The statistics that were used for validating are MAE, MBE, RMSE and D. The method that was used for bias correction was empirical quantile mapping Issues encountered, and as documented in the literature, include the unavailability of long periods of observed quality rainfall data and the limited and uneven spatial distribution of rainfall stations. Catchment rainfalls were estimated using observed rainfall, and this was assumed as the best estimate and was compared to the catchment rainfalls that were estimated using the biascorrected remotely sensed rainfalls. The performance of CHIRPS rainfall was varied among the approaches and the selected catchments. Nevertheless, the results from this study still show the potential of the use of remotely sensed rainfall to estimate catchment design rainfalls. At the daily timescale, satellite-derived and observed rainfall were poorly correlated and variable among locations. However, monthly and annual rainfall totals were in closer agreement with historical observations than the daily values. Despite the varied performance , the result of the study shows that CHIRPS rainfall product can be used to estimate catchment rainfall for hydrological modelling and flood frequency analysis. By acknowledging that the performance of remote sensing products is robust, it is of importance to note that the performance of the results presented is strictly for the catchments and stations selected for this project as well as the methods selected to validate and correct the bias in remotely sensed rainfall. The recommendations from the study are that a similar study is conducted in another region where there is even distribution of stations and a long record of quality observed rainfall beyond the year 2000 and consideration of the methods to identify outliers before making any meaningful estimations such as catchment rainfall from rainfall data.
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    Applying the social-ecological systems framework to understand impacts of flooding in the Palmiet River catchment.
    (2021) Dlamini, Londiwe Zola.; Stuart-Hill, Sabine Ingrid.; Sutherland, Catherine Grace.
    Accelerating urbanization in African cities is impacting the ability of urban ecosystem services to provide services to contribute to the wellbeing of people. Additionally, climate change presents increased urban risks such as the increased frequency and intensity of flooding. This thereby threatens human life and built infrastructure; and challenges the resilience of communities already strained by socio-economic challenges. Ecosystem services in urban catchments are poorly understood which further adds to the lack of understanding the value of natural resources in urban catchments and subsequently how to restore and protect vital natural resources in order to ensure ecosystem services delivery. The aim of the study is to understand how impacts of flooding decrease the resilience of the communities in the Palmiet River catchment located in Durban, South Africa, through applying the social-ecological system (SES) framework. The Palmiet River catchment is a dynamic and heavily urbanized catchment in which the Palmiet River extends 26km through its headwaters at an elevation of 510m flowing through the lower informal settlement at 18m elevation. The SES framework is an interdisciplinary approach to understanding biophysical and social aspects in a relational landscape – both of which can no longer be studied in isolation. The methodology of the study uses data collected from public community engagement forums to identifyspecific issues occurring within the catchment and understanding the roles of interested and affected stakeholders. Further, aerial photography images of the Palmiet River catchment from 1981 to 2016 were used to identify the rate of urbanization and terrestrial impacts; this data was additionally supported by drone images. A SES framework was applied for sub-sections of the Palmiet River catchment in order to develop a narrative for the total river catchment to improve understanding of societal actions of urbanization that impact the functionality of the Palmiet River. The findings of the study reflect that: 1) Flood events are occurring more frequently, and more peopleare at risk as the influx of people within the catchment increases and the land use/cover changes. 2) A collaborative social system with a strong governance unit exists within the Palmiet catchment. This has facilitated conversations amongst resources users and actorsin the rehabilitation of the resource system. This could potentially serve as a springboard for identifying viable areas for ecological infrastructure investments. 3) The social system has increased resilience within the catchment – however, this may change as flood events continue to increase in intensity and frequency. 4) The Palmiet River is a dynamic social-ecological system that presents challenges as well as opportunities for sustainable and integrative catchment management. The SES framework provided a tool to evaluate the social and ecological systems through which to assess thecurrent limitations for the Palmiet River to regulate flood events. 5) It was lastly necessary to identify ways in which sustainable urban design systems and ecological infrastructure could be used as a part of catchment management strategies to rehabilitate and enhance ecosystem services. It was concluded that the ecosystem services once offered by the Palmiet River catchment have been compromised byunprecedented rates of urbanisation, particularly impacts of growing informal settlements in the lower parts of the catchment as well as industrial areas in the upper parts of the catchment.
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    Detecting and assessing the impacts of outlier events and data availability on design rainfall and flood estimation in South Africa.
    (2021) Singh, Keanu Reeve.; Smithers, Jeffrey Colin.; Johnson, Katelyn Ann.
    Accurate Design Rainfall Estimation (DRE) and Design Flood Estimation (DFE) require long periods of quality-controlled data for the planning, design, operation, and improved flood risk assessment of hydraulic structures. However, observed hydrological data frequently include outlier events and there is a decline of hydrological monitoring in South Africa which may impact DRE and DFE. It is therefore necessary to assess the impact of outlier events and reduced data availability on DRE and DFE. The aims of this study were to: (a) assess the impact of outlier events on DRE and DFE in South Africa, (b) assess the performance of outlier detection methods under South African conditions, and (c) assess the impact of reduced data availability on DRE and DFE in South Africa. The impact of synthetic Low Outlier (LO) and High Outlier (HO) events on DRE and DFE from observed and synthetically generated data series were assessed. The performance of the BoxPlot, Modified Z-Score (MSZ) and Multiple Grubbs-Beck Test (MGBT) outlier detection methods were assessed. Record length and network density were reduced to assess the impact of reduced data availability on DRE and DFE. Results from the analysis of observed data show that design rainfall is impacted by up to 22% and design floods by up to 45% in the presence of LOs. Design rainfall is impacted by up to 16% and design floods by up to 46% in the presence of HOs. For synthetically generated data series, design rainfall and floods are impacted by up to 2% and 1% respectively in the presence of LOs and by up to 13% in the presence of HOs. At best, LOs in observed rainfall and streamflow data are under-detected by up to 6% and 30% respectively by the MGBT method, whereas HOs are over-detected up to 50% and 150% respectively by the MZS method. Design rainfall and flood events are impacted by up to 4% and 24% respectively by reduced record lengths, and by up to 4.5% and 60% respectively from a reduced gauged network. This study indicates that outlier detection be adopted as regular practice in South Africa and that additional national resources must be directed towards maintaining and improving the hydrological monitoring networks in South Africa.
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    Assessing the performance of techniques for disaggregating daily rainfall for design flood estimation in South Africa.
    (2020) Ramlall, Ryshan.; Smithers, Jeffrey Colin.
    Design Flood Estimation (DFE) and other hydrological modelling methods are used to limit the risk of failure and ensure the safe design of infrastructure and for the planning and management of water resources. The temporal distribution of rainfall has a significant impact on the magnitude and timing of flood peak discharges. Rainfall temporal distributions are therefore an important component of DFE approaches. In order to improve DFE methods which are based on event or continuous simulation rainfall-runoff models, it is generally necessary to use sub-daily time step rainfall hyetographs as input. However, the number of recording raingauges which provide sub-daily timesteps in South Africa is relatively scarce compared to those which provide daily data. Rainfall Temporal Disaggregation (RTD) techniques can be used to produce finer resolution data from coarser resolution data. Several RTD approaches have been applied in South Africa. However, application of RTD approaches locally is relatively limited, both in terms of diversity of approaches and cases of application, compared to those developed and applied internationally. Therefore, a need exists to further assess the performance of locally applied approaches as well update the list of available approaches through inclusion of internationally developed and applied RTD techniques. A pilot study was performed in which selected locally applied and internationally applied approaches were applied to disaggregated daily rainfall data. Some approaches were applied in their original form while others were modified. Temporal distributions of rainfall were represented by dimensionless Huff curves, which served as the basis for comparison of observed and disaggregated rainfall. It was found that for daily rainfall, the SCS3, SCS4 and Knoesen model approaches performed considerably better than the other approaches in the pilot study. The RTD approaches were further assessed using data from 14 additional rainfall stations. For the additional stations, the Knoesen model disaggregated depths provided the most realistic temporal distributions overall, followed by the SCS-SA approach. In additional, an adapted form of the Triangular distribution was found to show potential for disaggregation when a generalised value for the timing of the peak was utilised.
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    Water-use of commercial bamboo species in KwaZulu-Natal, South Africa.
    (2020) Gumede, Mxolisi Percyval.; Clulow, Alistair David.; Everson, Colin Stuart.; Everson, Theresa Mary.
    Abstract available in pdf.
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    Assessing the effects of site preparation treatments on erosion processes and sediment yield on a commercial Eucalyptus plantation: case study at Two Streams, KwaZulu-Natal.
    (2020) Bull, Jordan Michael.; Hill, Trevor Raymond.; Everson, Colin Stuart.
    Soil erosion monitoring and modelling is critical in the face of climate change, as erosion is detrimental to environmental and human health. It reduces soil productivity through degradation, compromises water quality through nutrient loading freshwater sources, and decreases reservoir capacity through sedimentation. This is a global challenge which is being amplified by increased levels of soil erosion on cultivated lands (e.g. commercial forestry), the combined effects of which hinder the success of several United Nations Sustainable Development Goals. However, commercial forestry is essential for human survival, providing a host of resources for human consumption, and expanding in its global coverage each year; although, this expanding need for commercial forestry creates a paradox, as it has the potential to damage environmental health and biodiversity (systems which humans rely on for survival), particularly through soil erosion and sedimentation of freshwater systems. Afforestation of plantations has been widely considered a land-use activity which reduces soil erosion; although, this is dependent on the management of the commercial plantations, where certain commercial forestry management techniques exacerbate soil erosion, such as the well-used site preparation technique of burning. Therefore, an investigation into the effect of commercial forestry site preparation techniques such as burning (at different severities) and mulching on soil erosion and the modelling thereof is required, as only a paucity of research has reported on this. Soil erosion measurements were conducted on a newly planted Eucalyptus dunnii stand, which consisted of three different site preparation techniques, namely a hot burn, a cold burn and a mulch treatment, in the Two Streams catchment, Kwa-Zulu Natal, South Africa. Micro-runoff and runoff plots were used to respectively measure splash and rill erosion of sediment, nitrogen, phosphorous, dissolved organic carbon, particulate organic carbon loss and runoff on each treatment at different slopes. In addition, soil erosion and runoff of this catchment and treatments were modelled using the ArcSWAT model, and the observations were used to validate the simulated outputs. The mulch treatment had the most consistent reduction in runoff and erosion, while the burn treatments of different severities generated greater respective runoff and erosion quantities through different erosional processes (splash vs rill). The ArcSWAT model over-simulated runoff on the hot burn and mulch treatment, while under-simulating on the cold burn treatment; however, the model consistently over-simulated sediment and nutrient loss on all treatments, indicating the model’s inability to simulate soil erosion on the defined land-use treatments. The reduced runoff and erosion produced by the mulch treatment is attributed to the protection that the mulch provides to the soil from splash erosion and the resistance posed to overland flow reducing rill erosion. The burn treatments generating more erosion and runoff through different erosional processes was attributed to the differing nature of debris produced by each burn severity. This research will contribute towards the data sets necessary to refine the land-use management tools of the ArcSWAT model to better model soil erosion on different land-use treatments. Furthermore, this research demonstrates the erosion processes that differing site preparation treatments are susceptible to, and what this means for future research and protecting soil and downstream water quality in the face of climate change.
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    The water balance of vermiculite covers on mining wastes in a semi-arid environment.
    (2019) McDonald, Johann.; Lorentz, Simon Antony.
    Deposition of large quantities of mining waste is an activity that can have a negative impact on surface and ground water resources. These impacts necessitate reclamation and amelioration of the wastes through various measures to reduce these impacts. Specific reclamation measures are therefore needed for mine closure and legal requirements. These requirements include covering the waste with a sustainable cover material which is then vegetated. Covers are mostly designed to restrict the ingress of water into the mine waste, from where water might move pollutants into the environment. Cover designs could also allow for natural attenuation/degradation of pollutants within the waste and often contribute to design stability. To act effectively, the covers need to be constructed of materials matched to the design and task. The primary task of the cover soil is to hold water for vegetation and and subsequently release it into atmosphere and so contribute to the integrity of the cover. Ideal materials are not always readily available and so some understanding of cover material characteristics are required before effectiveness of the cover’s contribution to the site water balance can be evaluated. The interaction of the waste cover with the waste material should also be evaluated for its contribution to sustainability and to the cover’s water balance. Knowledge of these interactions will always be beneficial, as the availability of water for the vegetation in the cover stays important for the stability of the cover. This benefit, though, is dependant on the pollution potential of the waste in relation to the cover material. Through a literature review the studied vermiculite cover design was identified as a type of store and release cover. The study subsequently evaluated the water balance mechanisms of vermiculite covers on mining wastes in its semi-arid environment. The cover material and the waste material’s hydraulic properties were evaluated to determine likely flux responses. Soil water volumetric water content status was used to confirm fluxes and water status in cover and waste materials. Surface runoff and lysimeter drainage measurements added information for the assessment of fluxes onto and below the cover material. The HYDRUS unsaturated/saturated soil water physics model was used to model and derive general estimates of the overall waterbalance, having been calibrated with physical results obtained from field observations and material characteristics that were determined in the field. The study yielded promising results for the use of vermiculite waste as a cover material in that it showed good store and release properties under varying rainfall intensities and should therefore not contribute excessively to ground water pollution under similar circumstances.
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    Development and assessment of an ensemble joint probability event based approach for design flood estimation in South Africa.
    (2019) Dlamini, Nkosinathi Sethabile.; Smithers, Jeffrey Colin.
    It has been reported that global climate change has impacted on the frequency as well as severity of flood events. Reliable flood estimates are required for managing and designing hydraulic structures, which is essential under extreme weather regimes in the future. Design flood estimation methods in South Africa are based on statistical analysis of past streamflow data, and rainfall based methods. Rainfall-based methods often have preference over streamflow-based methods for design flood estimation due to longer records of rainfall data that also have a greater spatial and temporal coverage than streamflow records. A key assumption in rainfall based methods for design flood estimation is the assumption regarding the exceedance probability of the estimated flood. It is generally assumed that the return period of the estimated flood will be the same return period as the input rainfall. This equality of rainfall and flood return periods is generally not true given the use of model parameters representing average conditions and the impact of antecedent moisture conditions on hydrological response. Hence, a Joint Probability Approach (JPA) where the key input model parameters, and not only the input design rainfall, are treated probabilistically will overcome the limitations associated with rainfall based design flood estimation. The underlying approach to the JPA is that instead of the use of a single combination of input variables to determine the flood characteristics, the method uses multiple combinations of flood producing parameters to determine the flood characteristics. In this study, a JPA was applied using the SCS-SA model, and the modelling framework used to determine the derived flood frequency curve is based on three principal elements. These include: (i) defining the key model inputs with their respective probability distributions and correlations, (ii) a stochastic model to synthesise sequences of the selected variables, and (iii) selecting an appropriate deterministic hydrological model to simulate the flood generation process, and use of the simulated outputs to derive the flood distribution. To evaluate the performance of the model, the results were compared to observed streamflow data. A statistical analysis was conducted in conjunction with graphs to verify the performance of the model. The Nash-Sutcliff Efficiency (NSE), absolute relative difference and Mean Absolute Relative Error (MARE) were used to evaluate the performance of the model. The results produced from applying the Ensemble SCS-SA model with rainfall that was fitted to the probability distribution of the 1 day design rainfall and sampling from the 90 % prediction intervals for each return period indicates that the model was performing relatively poorly in terms of estimating both the observed design runoff volume and design peak discharge for all the selected test catchments. The incorporation of the correlation between the rainfall depth and rainfall duration using a conditional probability distribution and in conjunction with the probability distributions of the other key input variables in the Ensemble SCS-SA model, resulted in significantly improved estimated runoff volume and peak discharges for all the catchments used. The Ensemble SCS-SA model has also shown potential and flexibility to deal with uncertainty by accounting for the distributed nature of the input variables and taking on values across the full range of their distribution in the modelling process, thus avoiding the potential of bias that can occur when adopting a single set of pre-determined input values. This study has shown the potential and flexibility of the Ensemble SCS-SA model to deal with uncertainty, providing opportunity for the expanded application of the model.
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    Estimation of water use efficiency of soybean (glycine max) for biodiesel production in KwaZulu-Natal.
    (2020) Reddy, Kyle Trent Cameron.; Kunz, Richard Peter.; Mabhaudhi, Tafadzwanashe.
    Abstract available in pdf.
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    Evaluating the influence of the land surface and air temperature gradient on terrestrial flux estimates derived using satellite earth observation data.
    (2020) Khan, Sameera.; Chetty, Kershani Tinisha.; Gokool, Shaeden.
    Abstract available in pdf.
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    Investigation of the potential use of the root-zone storage concept in hydrological modelling under South African conditions.
    (2019) Horan, Robyn.; Toucher, Michele Lynn.
    Hydrological models are currently an accepted method used in determining the impacts of Streamflow reduction activities (SFRA) in South Africa. However, the limited availability of soils and rooting depth data create high uncertainty within hydrological modelling exercises. Following poor simulations of streamflow, evaporation and soil water by the ACRU model at Two Streams and Cathedral Peak Catchment VI, the root- zone storage capacity was calculated for both catchments using three internationally published over the period 2007 to 2013 and 2014 to 2018, respectively. The input and calibration data used in the running of the ACRU model was undertaken using observed data commonly available for research catchments in South Africa. Additional data that was available for these specific catchments (observed evaporation and soil water at Two Streams and evaporation at Cathedral Peak Catchment VI) were used in the validation of results. The three methods produced similar mean root- zone storage capacities in both catchments but the Nijzink and DiCaSM methods produced the deepest root-zone storage capacity in the summer months. The results of the Nijzink method were the most variable and DiCaSM the least variable in both catchments. The Nijzink method was most sensitive to the actual evaporation in both summer and winter and sensitive to the precipitation in summer. The Wang method most sensitive to precipitation in summer. The DiCaSM method was found to not be sensitive to the rainfall in either season but highly sensitive to the actual evaporation year-round. The root-zone storage concept better reproduced the observed soil water throughout the soil profile at the Two Streams catchment than the ACRU model. The validation of the root- zone storage capacity against observed soil water illustrated that the root zone storage capacity reflects climate conditions rather than the soil depth and is independent of vegetation, soils and rooting characteristics. This study found that traditional methods of estimating the actual evaporation does not always capture the variability in timing and magnitude of evaporation. The most significant finding is that simple climate driven water balance routine could provide a better representation of soil water than a complex, layered model under South African conditions. The root-zone storage capacity could be a valuable tool in the improvement of hydrological modelling and fundamental in improving the precision of SFRA assessments in South Africa.
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    An assessment of the water use of indigenous and introduced tree SPP. and varying land uses around Vasi Pan, Maputaland, KwaZulu-Natal.
    (2017) Pearton, Tracy Ann.; Everson, Colin Stuart.; Chetty, Kershani Tinisha.
    Abstract available in PDF file.
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    Assessment of satellite derived rainfall and its use in the ACRU hydrological model.
    (2017) Suleman, Shuaib.; Chetty, Kershani Tinisha.; Clark, David John.
    Many parts of southern Africa are considered water scarce regions. Therefore, sound management and decision making is important to achieve maximum usage with sustainability of the precious resource. Hydrological models are often used to inform management decisions; however model performance is directly linked to the quality of data that is input. Rainfall is a key aspect of hydrological systems. Understanding the spatial and temporal variations of rainfall is of paramount importance to make key management decisions within a management area. Rainfall is traditionally measured through the use of in-situ rain gauge measurements. However, rain gauge measurements poorly represent the spatial variations of rainfall and rain gauge networks are diminishing, especially in southern Africa. Due to the sparse distribution of rain gauges and the spatial problems associated with rain gauge measurements, the use of satellite derived rainfall is being increasingly advocated. The overall aim of this research study was to investigate the use of satellite derived rainfall into the ACRU hydrological model to simulate streamflow. Key objectives of the study included (i) the validation of satellite derived rainfall with rain gauge measurements, (ii) generation of time series of satellite derived rainfall to drive the ACRU hydrological model, and (iii) validation of simulated streamflow with measured streamflow. The products were evaluated in the upper uMngeni, upper uThukela (summer rainfall) as well as the upper and central Breede catchments (winter rainfall). The satellite rainfall products chosen for investigation in this study included TRMM 3B42, FEWS ARC2, FEWS RFE2, TAMSAT-3 and GPM. The satellite rainfall products were validated using rain gauges in and around the study sites from 1 January 2010 to 30 April 2017. The rainfall products performed differently at each location with high variation in daily magnitudes of rainfall. Total rainfall volumes over the period of analysis were generally in better agreement with rain gauge volumes with TRMM 3B42 tending to overestimate rainfall volumes whereas the other products underestimated rainfall volumes. The ACRU model was applied using satellite rainfall and rain gauge measurements in the aforementioned study catchments from 1 October 2007 to 30 September 2016. Streamflow results were generally poor and variable amongst products. Daily correlations of streamflow were poor. Total streamflow volumes were in better agreement with total volumes of observed streamflow. TRMM 3B42 and rain gauge driven simulations produced the best results in the summer rainfall region, whereas the FEWS driven simulations produced the best results in the winter rainfall region.
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    The effect of the Lions River floodplain on downstream water quality.
    (2015) Ndlovu, Hlengiwe.; Jewitt, Graham Paul Wyndham.; Kotze, Donovan Charles.
    Wetlands provide important ecosystem services, including the purification of water. The uMngeni catchment is an important basin providing water to the cities of Pietermaritzburg and Durban, South Africa’s second largest economic hub. However, there are rising concerns over the deterioration of water quality in Midmar Dam, a large impoundment within this basin. The Lions River, one of the main tributaries to Midmar Dam, transports pollutants from its catchment, as well as the Mooi River catchment through the recently implemented Mooi-Mgeni transfer scheme (MMTS) into the impoundment. This study aims to establish a baseline ecological integrity and effect on downstream water quality of the Lions River floodplain, an important, but degraded, wetland in the uMngeni catchment, to provide a guide for the planning and implementation of rehabilitation interventions. A comprehensive assessment of the wetland’s structure was undertaken using vegetation and soil parameters, mapped and compared with an interpretation of landuse change within the wetland based on historical aerial photographs. The wetland’s impact on downstream water quality was assessed by sampling water at various points in the Lions River channel through the floodplain over a period of one year. The study found that the wetland’s ecological integrity has decreased due historical landuse in the floodplain. A comparison of soil wetness indicators which reflect the historic extent of the floodplain and vegetation wetness indicators which reflect the current extent of the floodplain suggest that although localised drying out of some areas has occurred, most of the historical floodplain area still supports wetland conditions. Wetness indicators of soil and vegetation indicate a transformation in the wetland’s water regime. A moderate to high abundance of ruderal and alien invasive species in 61% of the floodplain, particularly the drier areas of the floodplain, further indicate a reduction in ecosystem health. Hydrological processes emerge as the key drivers of species composition and historical landuse in the floodplain. Water quality results indicate that total oxidised nitrogen decreased from upstream to downstream whilst ammonia concentrations remained stable at all the sampling points. Soluble reactive phosphorus concentrations increased, while total phosphorus concentrations decreased from upstream to downstream. This study highlighted the importance of detailed field studies and understanding for rehabilitation planning to return ecosystems to their natural function.
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    Developing a method to estimate the water use of South African natural vegetation using remote sensing.
    (2016) Ramjeawon, Manish Roshenlal.; Toucher, Michele Lynn.; Mengistu, Michael Ghebrekidan.
    The scarcity of water is a growing concern throughout the world. It is essential to accurately determine the quantity and quality of this valuable resource to aid in water resource planning and management. For this purpose a hydrological baseline is required to compare against the water use of other land uses. Currently, the Acocks (1988) Veld Type is the baseline land cover used for hydrological studies. However, there are several shortcomings associated with this baseline land cover that may be overcome by using the recently released natural land cover map produced by South African National Biodiversity Institute (SANBI) 2012. A barrier to the use of the SANBI (2012) vegetation map is that, the water use parameters have not been determined for the various vegetation units defined. Vegetation water use can be determined by estimating the total evaporation (ET). There are a number of in-situ methods available to estimate ET. However, these methods estimate ET based on point or line averaged measurements which are only representative of local scales and cannot be extended to large areas because of land surface heterogeneity. The application of remote sensing energy balance models has the potential to overcome these limitations. Remote sensing has the ability to produce large spatial scale estimates of ET. It can also provide information at remote sites where it is difficult to install instruments. The focus of this study was to develop a method to estimate ET for natural vegetation of South Africa using remote sensing. The Surface Energy Balance System (SEBS) model in conjunction with Landsat 7 ETM+ and 8 OLI/TRS images was first used to validate point-based ET from various biomes across the country. The results from the study indicate a fair comparison between the in-situ ET data and the evaporation estimates produced using the SEBS model with coefficient of determination value of 0.66 being achieved and a RMSE of 1.74 The highest RMSE was attained for the Ingeli forest site whilst the lowest belonged to the Nama Karoo site of 2.2 and 0.5, respectively. The SEBS model was able to estimate ET which mimics the trend of in-situ ET well. However, the model tends to over-estimate ET in comparison to in-situ ET data. Following the validation of the in-situ and SEBS ET, the SEBS model was applied to model ET for a year. For this investigation, cloud free Landsat 8 OLI/TRS images was obtained for each biome for the period between 1 July 2014 to 31 June 2015. The highest ET value of 8.7 mm/day was obtained from the Forest biome on the 12 January 2015 and the lowest ET estimate of 0.09 mm/day was on the 17 January 2015 for the Nama Karoo biome. The Forest biome recorded the highest mean ET value of 4.9 mm/day whilst the lowest mean ET value was 0.71 mm/day attained from the Nama Karoo biome. Satellite derived ET using the SEBS model produced reliable estimates when compared to in- situ ET. The spatial and temporal resolution of ET can be achieved using remote sensing. The ET estimates from SEBS compared well to the in-situ ET measurements and followed the seasonal trend, however an over-estimation of ET was present in some cases. Overall, remote sensing proves a viable option to estimate ET over large areas. This method can be applied to derive the water use which can be used to determine water use parameters.
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    The potential impacts of up-scaled rainwater harvesting on ecosystem goods and services in the Potshini and Makanya catchments.
    (2016) Chetty, Andrea Simone.; Jewitt, Graham Paul Wyndham.; Horan, Mark John Christopher.
    Water scarcity is fast becoming a global concern, with at least each continent facing water-related issues regarding quantity, quality and delivery. An estimated 8.8% of South Africans do not have access to potable water, according to the World Wildlife Fund’s 2011 South African census (2016). The inaccessibility to water for domestic, agricultural or economic activities directly impacts on food security and poverty. Communities living in rural surroundings and depending directly on the environment to support their livelihoods are most affected by water shortages. The 1.2 km2 Potshini Catchment, located in the foothills of the Drakensburg Mountains in South Africa, and the 300 km2 Makanya Catchment, situated on the western side of the South Pare Mountains in Tanzania, provide good case studies to assess how communities, vulnerable to poverty and food security, cope with water shortages. Both catchments have well-established rainwater harvesting (RWH) networks that supplement the rainfed subsistence crops. RWH is a method of capturing, conveying and storing rainwater and runoff for future use. It is a valuable practice in agriculture, intended to improve the availability of water to crops towards the end of high rainfall months and during dry-spells. The conservation of water, in these instances, has the potential to secure and improve livelihoods, and to lessen the pressure placed on ecosystem goods and services. Albeit that RWH is an alternative water innovation, supporting the ideals of integrative water resource management, the impacts of up-scaled RWH on streamflow are still to be determined. Little is known about how ecosystem goods and services will respond to the expansion of RWH, as well as the presence of a feedback mechanism. Therefore, the aim of this study was gain a better understanding of the nature of RWH and its potential impacts on the environment in the form of a literature review. Secondly, a hydrological method or tool was developed to understand the impacts of RWH on ecosystem goods and services, in order to improve the catchment management of upstream and downstream communities alike. This was achieved by determining the relevant ecosystem goods and services within each catchment. Thereafter, the impacts of RWH on streamflow and soil moisture were determined by hydrological modelling of each catchment, using the ACRU Model. Using a scenario-based approach, the limits to RWH may be determined by increasing the level of water harvested in each case. Once the significance of this has been determined, the impact on related ecosystem goods and services can be understood. The Makanya and Potshini Catchments are located in rural settlements, whose population relies mostly on the environment for daily survival. Ecosystem goods and services, such as water supply and regulation, are high priority benefits. Water is supplied, filtered and purified through natural processes in the environment, whilst floods and droughts are regulated. Through the promotion of infiltration and reduced flow velocities by vegetation, the ecosystem controls the harsh effects of natural variability. Soil formation and retention assists the growth of crops through the facilitation of soil water infiltration and the transport of nutrients from the topsoil. Other basic goods and services within the catchments are the provision of food (fauna and flora), raw materials, and natural habitats for breeding, as well as cultural and recreational areas. The ACRU Model was successful in simulating daily streamflow and soil moisture in the Makanya and Potshini Catchments. A general reduction in streamflow as a result of increased RWH was modelled over the 56-year study period between 1952 and 2007, for both catchments. A virtual dam within the ACRU model is created to capture rainfall. Increased RWH scenarios are based on 30%, 60% and 90% of the current RWH conditions. It has been estimated that harvesting runoff in the drier months of the year could have the greatest impact on the environment, as low flows are initially reduced by a lack of rainfall. As RWH was increased, a gradual reduction in baseflow was modelled for the Potshini Catchment, whilst baseflows were reduced to zero mm in the Makanya Catchment, as rivers ran dry in low rainfall seasons. When compared to the baseline, the cumulative streamflow over the study period was reduced by 50% and 30%, respectively, in the Makanya and Potshini Catchments. This reduction was significant at all levels (30%, 60% and 90% increase in RWH relative to current conditions) of RWH in Makanya, whilst scenarios up-scaling RWH over 60% had a significant impact on the ecosystem in Potshini (95% confidence interval based on a t-test). The introduction and up-scaling of RWH had a positive impact on soil moisture, increasing total soil water content values far above the baseline values. Harvested water is allocated for irrigation to improve crop yields. Increased water availability improved crop yields up to 50% (assuming no other crop stress occurred), particularly in the Potshini Catchment, thus potentially improving food security within rural communities. Improved soil moisture through RWH acts a means of mitigating the reduction of streamflow downstream. Water is reallocated in the ecosystem and used to improve the delivery of goods and services for human benefit. Whilst, the environment may have the ability to absorb the initial shock, the continual expansion of RWH has the potential to reduce the resilience of the environment and the goods and services they provide. The large-scale employment of RWH over a long period can attest to a portion of the degradation found in the Makanya Catchment. This is commonly known as a negative feedback mechanism. As a result of improved crop yields, greater expanses of the catchment are converted to runoff generation areas, to increase the opportunities for harvesting water. As agriculture expands and population densities increase, further threats to the environment are created. Although future predictions cannot be accurately made, it is necessary to attempt to understand the possible outcomes of various theories. The accuracy of this scenario-based research is limited by the accuracy by which each scenario represents RWH, the accuracy with which ACRU represent all key processes and quality of historical data used. However, this study presents a method to determine the likely limits to up-scaling RWH in water-scarce regions, in order to safeguard the integrity of the environment for future generations.
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    Development and assessment of rules to parameterise the ACRU model for design flood estimation.
    (2015) Rowe, Thomas James.; Smithers, Jeffrey Colin.; Schulze, Roland Edgar.; Horan, Mark John Christopher.
    Design Flood Estimation (DFE) is essential in the planning and design of hydraulic structures. Recent flooding in the country has highlighted the need to review the techniques used to estimate design floods in South Africa, where old and outdated methods are widely applied. In this study the potential of a Continuous Simulation Modelling (CSM) approach to DFE in South Africa is highlighted, identifying the benefits of a CSM approach over event based approaches. The daily time-step ACRU agrohydrological model has provided reasonable results for DFE in several pilot studies. A review on hydrological modelling and the links and similarities between the SCS-SA and ACRU models, however, highlighted that in terms of land cover information, the land cover classification used in the SCS-SA model accounts for different land management practices and hydrological conditions, which are not accounted for in the current versions of the ACRU land cover classification. Since the CNs used in the original SCS model were derived from observations, and the SCS-SA model is an accepted method of DFE in small catchments in South Africa (Schmidt and Schulze, 1987a; Schulze et al., 2004; SANRAL, 2013), it was assumed in this study that the design volumes simulated by the SCS-SA model are reasonable, and that the relative changes in design volumes simulated by the SCS-SA model as a consequence of changes in land management practice or condition are also reasonable. Based on these assumptions, the general approach to the study was to investigate how design volumes simulated by the SCS-SA model for various land management practices or conditions could be simulated by the ACRU model, and to derive classes in the ACRU hierarchical classification for land management practice and hydrological condition. Consequently, design runoff volumes and changes in design runoff volumes, for different management practices and hydrological conditions, as simulated by the SCS-SA model, were used as a substitute for observed data, i.e. as a reference, to achieve similar design runoff volumes and changes in design volumes in the ACRU model. This was achieved by adjusting relevant variables in the ACRU model to represent the change in management practice or hydrological condition, as represented in the SCS-SA model. After three initial attempts failed to produce comparable simulation results between the SCS-SA and ACRU models a sensitivity analysis of ACRU variables was conducted in order to identify which ACRU variables would represent SCS-SA Curve Numbers (CNs) best for selected land cover classes. The sensitivity analysis identified two ACRU variables best suited to achieve this task, namely QFRESP and SMDDEP. Calibration of QFRESP and SMDDEP values against CN values for selected land cover classes was performed. A strong relationship between these ACRU variables and CN values for selected land cover classes was achieved and consequently specific rules and equations were developed to represent SCS-SA land cover classes in ACRU. Recommendations, however, are suggested to further validate and substantiate the approach and developed rules and equations.
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    Assessing the performance of regional flood frequency analysis methods in South Africa.
    (2015) Nathanael, Jermaine Jonathan.; Smithers, Jeffrey Colin.; Horan, Mark John Christopher.
    In engineering and flood hydrology, the estimation of a design flood refers to procedures whereby the magnitude of a flood is associated with a level of risk at a given site (Pegram and Parak, 2004). The use of a Regional Flood Frequency Analysis (RFFA) approach improves the accuracy and reliability of estimates of design floods. However, no RFFA method is currently widely used in South Africa, despite a number of RFFA studies having been undertaken, that include South Africa. Hence, the performance of the current RFFA approaches needs to be assessed in order to determine the best approaches to use and to determine if a new RFFA approach needs to be developed for use in South Africa. Through a review of the relevant literature it was found that the Meigh et al. (1997) Method, the Mkhandi et al. (2000) Method, the Görgens (2007) Joint Peak-Volume (JPV) Method, which uses a K-Region regionalisation, as well as a Veld zone regionalisation, and the Haile (2011) Method are most suitable for application in a nationwide study. Each regional approach was assessed by comparing their design flood estimates with those estimated from an at-site flood frequency analysis of the observed flood data, using both the General Extreme Value (GEV) and Log Pearson Type 3 (LP3) distributions. However, due to the LP3 distribution producing inconsistent design flood estimates, it was removed from further analysis and only the GEV distribution was assessed. Annual Maximum Flood (AMF) data were obtained from the Department of Water and Sanitation (DWS) for 1458 stations across the entire country. In addition to these datasets, 89 synthesised dam inflow records were obtained from the DWS and incorporated into the study. Due to a thorough data screening process, the final number of stations and dam inflow records analysed was reduced to 407 stations. In order to determine the overall accuracy of the RFFA methods, Relative Errors (RE) (%) were calculated at each station. Box plots and frequency plots were utilised to represent the distribution of relative errors and the degree of bias was measured using a ratio of the estimated and observed design floods. The results of the study show that the Haile Method generally performs better than the other RFFA methods, however it also consistently under-estimates. The Mkhandi Method generally over-estimates. The Meigh Method generally performs the worst, consistently over-estimating. For the JPV Methods, the K-Region regionalisation generally performs better than the Veld zone regionalisation; however, they both consistently over-estimate design floods. The poor overall performance of the RFFA methods are due to a number of reasons. In the case of the Mkhandi et al. (2000) Method, the tests for homogeneity that were developed were too lenient, which may have incorrectly defined regions as being homogeneous. In the case of the Meigh et al. (1997) Method, the regionalisation of homogeneous flood regions were too broad, where only two flood regions have been identified for South Africa. For the Haile (2011) Method, the logarithmic regressions developed for a number of regions were not able to determine index floods for all catchment areas. Therefore, power regressions were developed in this study. In the case of the JPV Methods, the Kovacs K-Regions and Veld zone regions were used, which have not been updated in the past several years. In response to the generally poor performance of the RFFA methods assessed in this study, it has been recommended that a new method be developed for application in design flood practice in South Africa.