Doctoral Degrees (Civil Engineering)

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Hydraulic impacts and management of intermittent water supply
(Stellenbosch : Stellenbosch University, 2023-03) Loubser, Carlo; Jacobs, Heinz; Wium, Jan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Various challenges, such as limited freshwater resources, climate change impacts, rapid population growth, urbanisation and underinvestment in water supply infrastructure, have led to intermittent water supply (IWS) in potable water distribution systems. Earlier research has confirmed that IWS negatively impacts the consumers, the infrastructure and the water supply authorities. In potable water distribution systems, water quality is of the utmost importance. In systems subjected to IWS, water quality is often compromised. However, there is a large body of literature addressing issues related to water quality in IWS systems. In contrast, a number of more elementary and hydraulic aspects related to IWS systems have not been researched in depth. This research sets out to answer the following questions that are unrelated to water quality, but instead focusses on the hydraulics and infrastructure elements of the IWS systems. Is IWS prevalent in South African water supply systems? Can IWS be avoided in urban areas faced with water scarcity and which mechanisms are available to water services providers to avoid having to implement IWS? Can a model be developed to crudely assess the pipe infrastructure in order to evaluate whether IWS is a threat based on the potential maximum capacity of the network? How can systems subjected to IWS be compared in a quantifiable manner? And, how can the reliability of supply be assessed in systems subjected to IWS and what are the potential consequences of unreliable supply schedules? Earlier research on the global prevalence of IWS indicated that South Africa practises continuous water supply. Data on IWS in South Africa was collated by considering four different source types. The data were spatially and temporally analysed to determine the prevalence of IWS in South Africa. The population affected by IWS increased by ~26% between 2008 and 2017, which exceeds the population increase of ~12% over the same period. Moreover, 22 million people in South Africa were affected by IWS in 2017. Results from this research confirm an increased prevalence of IWS over time and show that 65 of the 231 municipalities in South Africa supplied water intermittently; 32 had continuous water supply and no data was available for the remainder. The outcomes highlight the widespread occurrence of IWS in South Africa. Between the years 2015 and 2018, the City of Cape Town, South Africa, experienced the worst drought on record, which placed tremendous pressure on the city’s bulk water resources. Despite many of the major dams nearly running dry in the summer of 2017/2018, and the available water diminishing to only a few months of supply, the City of Cape Town managed to avoid implementing IWS. This research presents the various strategies adopted and implemented by the City of Cape Town in order to avoid IWS. The successes achieved led to the City of Cape Town reputedly becoming the number one water saving city in the world in October 2018, saving as much as 500 ML per day, which equates to about half the normal demand before the drought. Given the well-known and widely published negative impacts associated with IWS, it would be useful for water services providers in water scarce regions to take cognisance of how the City of Cape Town managed to avoid implementing IWS. Planners are often faced with the challenge to provide crude estimates of water distribution system infrastructure capacity and associated cost in the early phases of greenfield developments. This research investigated the relationship between physical and hydraulic characteristics of a water distribution system and the corresponding serviced area. A model was compiled linking the total pipeline length of a water distribution system to the peak flow rate. The model enables prediction of the total length of water distribution system pipes required to service a future development area as a function of the peak flow rate. Alternatively, the model can estimate the potential maximum peak flow rate that can be supplied if the total pipeline length is known. IWS can result from several potential causes, including inadequate overall pipeline length or a lack of network reinforcements when new developments are added on the fringes of developed areas. Systems subjected to IWS due to these causes could be expected to have insufficient overall pipe length or different diameter distributions when compared to the model results. Thus, the model would allow a user to ascertain whether an existing water distribution system has potentially been stretched beyond its design capacity. Water supply authorities need tools to help understand IWS and the associated implications. A new indexing framework involving the causes and impacts associated with IWS has been developed. In addition, a novel approach allows for quantification of the severity of IWS based on knowledge of a few readily available inputs. The indexing framework and quantification tool could lead to improved understanding of IWS and could assist water supply authorities faced with IWS to make informed decisions. Two towns located in the Mpumalanga Province of South Africa, had IWS implemented for a number of years prior to this study. While the general causes and impacts of IWS are fairly well researched and documented, the causal-consequential pathways of IWS as experienced in one of the study areas, offer a new perspective on consumer acceptance and conduct related to various forms of IWS. Logging of flow rates recorded by meters supplying water intermittently, also offers new information on supply availability, supply durations and reliability of supply when supply schedules are managed by manually opening and closing of zone valves. Unreliable and unavailable supply led to an increased number of illegal connections. Once water theft and leakage rates exceeded certain levels, the water services provider struggled to maintain control over the water supply infrastructure and a spiral of decline was observed.
Road network supply efficiency in Cape Town, South Africa and its link to the incidence of road traffic crashes: an evaluation of equity
(Stellenbosch : Stellenbosch University, 2023-03) ter Huurne, Dominique Andrea; Sinclair, Marion; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: The Road Safety Problem, including its devastating effects on human livelihoods and socioeconomic development, is well-documented at both the global and local scales. In South Africa, road safety (especially for vulnerable road users) is a short-term strategic priority. The focus is shifting from reactive to proactive approaches to crash-risk assessment. The disadvantage of proactive approaches is that they require extensive input data: road inventory data, exposure data, and environmental data, which is typically unavailable in low- and middle-income countries like South Africa. In its latest road safety strategy, the City of Cape Town set an objective to conduct road safety assessments on all class 1 to class 3 roads by 2018; this objective was not achieved. There is a need for a network-wide road safety measure that uses frugal and/or readily available data inputs. This study examined the relationship between crash frequency and transport demand in the City of Cape Town. Commercially available Origin-Destination Floating Car Data and trajectory clustering were used to determine the city’s transport demand corridors for various input parameters. The Cross K-function was employed to assess the spatial relationship between these corridors and fatal and serious injury road traffic crash locations (2015 to 2017) at the city and census-suburb scales. Furthermore, the transport demand corridors were used to evaluate road supply network efficiency (class 1 to 3 roads) as well as this efficiency measure’s potential as a road safety measure and an indicator of infrastructure vulnerability (transport equity). This was believed to be extremely relevant in the context of South Africa’s intention to focus the application of road safety assessments on mobility roads, as the majority of pedestrian crashes have been found to occur on access roads. Road network supply efficiency was quantified using the Collective Remoteness Indicator (CRI). A simple linear correlation test was conducted between 1) the CRI and crash frequency and density, and 2) the CRI and the South African Index of Multiple Deprivation 2011. For all alternatives analysed at the city scale, road traffic crash locations and transport demand corridors were found to be positively related at all 10-m intervals between 10 m and 200 m. The study also revealed positive spatial relationships for various census suburbs, particularly for pedestrian crashes during the morning peak period.Moderate to strong correlations between the CRI and crash density were discovered at the census-suburb scale, suggesting that road supply network efficiency has the potential to be applied as a measure of road safety. A subsequent qualitative analysis found potential for road supply network efficiency to be applied as an indicator of infrastructure vulnerability. This novel road safety measure is deemed to be of practical value to identify and prioritise sites or areas for road safety assessments.
The development of a daily stochastic streamflow model for probabilistic water resource management
(Stellenbosch : Stellenbosch University, 2023-03) Hoffman, Jahannes Jacobus; Du Plessis, Jakobus Andries; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: An ever-increasing water demand with limited supply of water in South Africa means that the focus of resource management needs to shift from a macro-level to micro-level. Well-defined research methodology regarding the management of larger water resource systems does exist in models such as STOMSA (Stochastic model of South Africa) and WRYM (Water Resources Yield model), which use monthly timesteps. In analysing smaller catchments, these macromodels need to be adapted to daily timesteps to enhance applicability in the management of resource systems for smaller local authorities. This research focused on the development of a daily stochastic streamflow model to be used in small, single site catchments for resource management by local authorities in South Africa. Such catchments usually consist of abstraction weirs with off-channel storage dams that should deal with the effects of short runoff response time associated with small catchments, where the monthly timestep analysis typically cannot account for the short-term variability in daily streamflow. The methodology used in the current research focused on the generation of daily stochastic streamflow data by retaining the day-to-day relationship of the historical streamflow series without the reliance on disaggregation models to generate daily data from larger timesteps. This was achieved by implementing a Markov process, as the core element, to generate the stochastic data, based on the day-to-day relationship of the historical daily dataset. To address seasonality associated with daily datasets, the concept of daily duration curves was introduced, which served as both a normalisation process of the historical data, as well as a statistical distribution for the random selection of stochastic streamflow data. To ensure repeatability, a Pseudo-Random Number (PRNG) generator was used in the randomisation process of generating the stochastic datasets. The Daily Markovian Stochastic Streamflow model (DMASS) was developed consisting of four modules. The Pre-processing Module used primary streamflow data from the Department of Water and Sanitation (DWS) to generate the daily streamflow time series. The Analysis Module analysed the daily streamflow time series to create the Daily Duration Curves (DDC) and the Cumulative Transition Probability Matrix (CTPM). The Generation Module used the DDC and CTPM to generate the stochastic sequences. The Climate Change Module provided the option to adjust the DDC according to the selected adjustment parameters.
The time-dependent behaviour of cracked textile reinforced concrete (TRC)
(Stellenbosch : Stellenbosch University, 2023-03) Alexandre, Vital Jorge Fisch; Combrinck, Riaan; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: The use of concrete faces drawbacks in the form of anthropogenic carbon dioxide emissions and a lower tensile strength threshold. The use of textile-reinforced concrete (TRC) is sought to tackle both these issues. Firstly, TRC elements provide an option for thinner structural elements and secondly, it improves the concrete’s post-crack behaviour when considering the short-term loading. However, there is limited research on the behaviour of TRC when subjected to long-term uni-axial loading, mainly due to the time-consuming nature of such related investigations. The purpose of this study is to investigate the behaviour of TRC composites when subjected to various sustained uniaxial loading levels for sustained time periods. This is accomplished by conducting both short- and long-term tests. The short-term investigations focus on the interaction between the textile and matrix and are assessed by delving into the pull-out of yarns from the matrix and uniaxial tensile strength tests. The long-term behaviour is investigated by performing tensile creep tests on predamaged and non-damaged specimens. The sustained loads applied ranged between 10 % and 75 % of the ultimate tensile static load test results. The single-yarn pull-out tests showed that the pull-out behaviour depends on the embedment length. Shorter lengths (25 and 35 mm) exhibited strain-softening behaviour with pull-out being the dominant failure mechanism. If the embedment length increases (30, 40, and 60 mm), then strain-hardening dictates the pull-out behaviour. Pull-out was found to be the failure mechanism for the 30 and 40 mm lengths and rupturing for the 60 mm embedment length. Additionally, the dynamic stage of the pull-out response was also identified to be associated with a bottleneck mechanism forming. This mechanism results from the imprint the warp yarn leaves in the matrix, constricting and dilating the extraction pathway. Particle fragments also cause congestion of the pathways, increasing the pull-out resistance. The uniaxial static pull-out tests were conducted with specimens containing two to six layers of textiles. It was discovered that the number of weft yarns in the observed section dictated the maximum number of cracks formed when considering the crack saturation. All samples also showed a ductile failure attributed to the telescopic failure mechanism. Moreover, the stiffness degradation showed that the samples failed when the secant modulus lowered to 2 GPa. The latter occurred regardless of the number of cracks and number of textiles, indicating that stiffness was related to the failure as opposed to the reinforcing area. The stiffness degradation is argued to be tied to the telescopic mechanism taking place. The sustained uniaxial load tests showed that the time-dependent strain increased with time and increasing sustained load level. The samples with a stress-level below 60 % did not fracture during the period over which the loads were sustained. However, the samples loaded at 75 % stress levels fractured within 10 minutes of loading. The residual strength tests also highlighted that the straightening of fibres during the sustained loading period, known as the training effect, enhanced the strength of the specimens compared to samples that were not subjected to sustained loads but with the same specimen age. Pre-damaged specimens also exhibited lower time-dependent strains compared to those with no predamage. This observation is also attributed to the training effect. The implications of the training effect was also noticed when considering the loading history of samples by increasing the stress level for a select few specimens.
The application of commercial floating car data for speed-based traffic state evaluation in the Sub-Saharan African context
(Stellenbosch : Stellenbosch University, 2023-03) Bruwer, Megan Melissa; Andersen, Simen Johann; Walker, Ian; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
ENGLISH ABSTRACT: Floating car data (FCD) are traffic data that are passively reported from within the traffic stream by GPSenabled probe devices commonly carried in vehicles, including smartphones, on-board navigation devices, and vehicle tracking systems. Commercial FCD are collected, aggregated, stored, and sold by third-party traffic data entities, providing network-wide speed, travel time, and origin-destination data. Commercial FCD eliminate the need for traffic sensors and communications networks, while simultaneously reducing the data analysis demands typical of Big Data because commercial FCD are characteristically made available in structured and readily usable formats. Commercial FCD are poised to become a primary source of traffic data in low- and middle-income countries where traditional, sensor-based traffic data are only sparsely collected over a vast road network, thereby leapfrogging the extensive traffic data collection systems established in high-income countries. Presently, commercial FCD are not widely used or researched in Sub-Saharan Africa. This dissertation is, therefore, well timed in its aim to assess the correct application of commercial FCD in the Sub-Saharan African context. This dissertation identified that the sample providing commercial FCD results in an inherent bias (called sample bias) because the reporting devices are purchased according to socioeconomic status, particularly in Sub-Saharan Africa, where average income, smartphone penetration and technology uptake is low. This dissertation represents the first time that the term sample bias has been described and systematically investigated as a characteristic of commercial FCD. The research found that commercial FCD are impacted by sample bias according to the socioeconomic, demographic, and geographic distribution of the sample that reports FCD in Sub-Saharan Africa. Sample bias was also proven to impact the accuracy of FCD speeds to the extent that speed accuracy differed between cities in South Africa and between commercial FCD sources. Mathematical models for the correct application of FCD in Sub-Saharan Africa that can be applied irrespective of sample bias, were then considered. Sample bias can be excluded in congestion measurement using ratio indices. FCD were found to enable accurate and comparative congestion measurement, both of recurrent and non-recurrent congestion, using variations of the Speed Reduction Index. Finally, three unique use-case studies, specifically applicable to Sub-Saharan Africa, were carried out to demonstrate the usefulness of FCD to evaluate the impact of roadworks projects, identify potholes along rural routes, and map changes in traffic patterns during the COVID-19 pandemic. The primary contribution of this research will be to steer Sub-Saharan Africa towards applicable use-cases of commercial FCD for transport planning purposes. This dissertation should allow commercial FCD to be applied with confidence for the correct use-cases in Sub-Saharan Africa. This research has provided a guideline for the evaluation of potential sample bias and the impact thereof, demonstrated the huge potential for FCD-based traffic pattern monitoring in a Sub-Saharan African context – for both urban and rural applications – and suggested future research for continued Sub-Saharan-specific FCD application. This research is critical to guide commercial FCD towards a significant role in providing primary traffic data over the extensive road network of our continent.

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