Browsing by Author "Du Plessis, J. A."

Now showing 1 - 6 of 6
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    Catchment parameter analysis in flood hydrology using GIS applications
    (South African Institution of Civil Engineering, 2012-10) Gericke, O. J.; Du Plessis, J. A.
    ENGLISH ABSTRACT: The use of Geographical Information Systems (GIS) has permeated almost every field in the engineering, natural and social sciences, offering accurate, efficient, reproducible methods for collecting, viewing and analysing spatial data. GIS do not inherently have all the hydrological simulation capabilities that complex hydrological models do, but are used to determine many of the catchment parameters that hydrological models or design flood estimation methods require. The purpose of this study was to perform catchment parameter analysis using GIS applications available in the ArcGISTM environment. The paper will focus on the deployment of special GIS spatial modelling tools versus conventional manual methods used in conjunction with standard GIS tools to estimate typical catchment parameters, e.g. area, average catchment and watercourse slopes, main watercourse lengths and the catchment centroid. The manual catchment parameter estimation methods with GIS-based input parameters demonstrated an acceptable degree of association with the special GIS spatial modelling tools, but proved to be sensitive to biased user-input at different scale resolutions. GIS applications in an ArcGISTM environment for the purpose of catchment parameter analyses are recommended to be used as the standard procedure in any proposed hydrological assessment.
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    Integrated water demand management for local water governance
    (Stellenbosch : University of Stellenbosch, 2010-12) Du Plessis, J. A.; Muller, J. J.; University of Stellenbosch. Faculty of Economic and Management Sciences. School of Public Leadership.
    Please refer to full text for abstract
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    Investigation into increasing short-duration rainfall intensities in South Africa
    (Water Research Commission, 2015-04) Du Plessis, J. A.; Burger, G. J.; Civil Engineering
    Extreme storms in South Africa and specifically in the Western Cape have been responsible for widespread destruction to property and infrastructure, even leading to displacement and death. The occurrences of these storms have been increasingly linked to human-induced climate change that is expected to cause more variable weather. Studies on climate circulation models for future climate conditions project that rainfall in the Western Cape and wider South African region is to become more intense and extreme. Sub-daily rainfall for 3 stations in the Western Cape and 4 stations in the rest of South Africa were analysed in order to determine if any trends towards more intense and extreme rainfall are observed and whether the trend is unique to the Western Cape or indicates a wider trend. This study explores this expectation by using historical short-duration rainfall (less than 24 h) for 7 stations in the Western Cape and South African region. Digitised autographic and automatic weather station 5-min rainfall data were combined to extend the effective record length. Both the magnitude and frequency of occurrence of rainfall events were analysed to assess if rainfall intensities are showing any evidence of increasing over time. For the magnitude of rainfall events, extreme value theory was applied to non-stationary sequences, using both a parametric and non-parametric approach for both event maxima and peaks over threshold modelling. The frequency analysis entailed measuring the frequency of exceedance of rainfall events over a certain threshold value. Both the magnitude and frequency analysis indicated that the combination of the two record types influenced the results of some of the stations, while the others showed no consistent evidence of changing rainfall intensities. This led to the conclusion that, from the available observed short-duration record, no evidence was found of trends or indications of changes in rainfall intensities.
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    An investigation into the evidence of seasonal rainfall pattern shifts in the Western Cape, South Africa
    (South African Institution of Civil Engineering, 2017-12) Du Plessis, J. A.; Schloms, B.
    ENGLISH ABSTRACT: Climate change is a highly contentious topic in the modern world. There is much evidence to indicate that climatic shifts and extreme weather anomalies are taking place globally, in some places more than others. This paper presents the findings on research to determine whether shifts in seasonal rainfall patterns are indeed already visible in historical rainfall data in the Western Cape of South Africa. The paper aims to provide some baseline information which can stimulate further research in this field. Different analytical methods were formulated to investigate the relationships between daily rainfall indices over a set timescale. Data was collected from the South African Weather Service (SAWS) in order to accumulate 20 rainfall stations, each with at least 100 years of historical daily rainfall data. Statistical analysis, linear trend line distributions, time lag comparisons, cumulative distributions, moving average plots and autocorrelation relationships were applied to the data. The results of the analysis indicated that (1) the rainfall season undergoes fluctuations of wetter and drier years (approximately 20-year cycles), (2) the South Coast region exhibits a shift towards a longer rainfall season, and in contrast the Mediterranean region is shifting to a shorter rainfall season when linear trend lines were analysed, and (3) the moving average plots showed only isolated seasonal shifts at the boundary months.
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    Planning for desalination in the context of the Western Cape water supply system
    (South African Institution of Civil Engineering, 2017-03) Blersch, C. L.; Du Plessis, J. A.
    ENGLISH ABSTRACT: As water demands continue to grow, South Africa is starting to consider seawater desalination as a potential future supply source, and it is currently being investigated at a feasibility level in a number of coastal cities, including Cape Town. Desalination is different to conventional surface and groundwater supply sources in that it is climate-resilient, having an assurance of supply of essentially 100 percent. However, the increased reliability comes at a great cost. This paper presents a methodology developed for modelling a proposed desalination plant as an integrated component of the Western Cape Water Supply System, in order to optimise system operating rules and cost. The modelling entailed short-term and long-term system analyses in the Water Resources Yield Model and Water Resources Planning Model, and estimation of first-order capital and operating costs in order to calculate and compare Unit Reference Values. The maximum increase in yield was found to occur when the seawater desalination plant is used as a base supply, operational all the time. There was little benefit, in terms of system yield, in using the desalination plant as an emergency supply source only. Unit reference values for the desalination plant decrease as the percentage supply from the plant increases, meaning that the lowest possible cost per cubic metre of water supplied is when the desalination plant is used as a base supply. It was also apparent that the unit reference values decrease with an increase in desalination plant capacity, suggesting that, from an economic perspective, the optimal solution would be to have one large desalination plant operational immediately.
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    Scoping phase comparison of development opportunities by making use of publicly available sustainability information
    (Elsevier, 2017) Du Plessis, J. A.; Bam, W. G.
    With sustainable business strategies and sustainability reporting now a norm, the public domain has in recent years been flooded with sustainable development information from a wide range of organizations. Although this information is generally retrospective in nature, an opportunity exists to make use of this information to compare the impact of different development opportunities prospectively, based on the performance of similar industries elsewhere. This paper therefore evaluates the potential of using publicly available sustainability information to enhance scoping phase decision-making by policymakers in order to prioritize projects that have the most potential for creating sustainable outcomes. The paper outlines a concept model for using sustainability information to compare development opportunities, followed by an analysis of five prominent international sustainability reporting frameworks at the hand of specific criteria to establish which framework would be most suitable to serve as basis for such a model.