Browsing by Author "Van Zyl, Jakobus E"

Now showing 1 - 11 of 11
  • Thumbnail Image
    Item
    Open Access
    Advanced water metering and its application in low income communities
    (2017) Malunga, Masoabi; Van Zyl, Jakobus E
    In South Africa, it is a legislative requirement that all water supply points be metered (van Zyl, 2011). Conventional meters are mostly used as the main means of monitoring water consumption by South African municipalities. In the last two decades, the water metering industry has seen substantial developments with new capabilities added to the conventional water meter, known as advanced meters. These advanced water meters have capability of processing, storing and communicating data without the need of human intervention. As such they come with desirable capabilities for both consumers and municipalities. These include prepaid meters which are special type of advanced water metering technology that is mostly applicable in the low income areas of South Africa. However, advanced water meters have significant drawbacks, such as higher failure rates (due to electronics, batteries and more components), higher purchase and maintenance costs and susceptibility to tampering. It is therefore necessary to make a conscious and informed consideration when deciding on which metering technology to implement for different users. This could be achieved through having a technology evaluation framework. The goal of this research was to develop an evaluation framework to help municipalities in the selection of appropriate advanced water metering technologies for application in low income communities. This goal was achieved through: determining the range of functionality of technologies both available and under development for advanced water metering; documenting case studies of both successful and failed implementation of advanced water meters, including social perception and impacts; developing an evaluation framework that can evaluate advanced water metering; and evaluating on technical, social, economic and environmental grounds. The results from literature and case studies indicate that in low income communities, advanced water metering is mainly implemented for cost recovery purposes. However, some municipalities implement advanced metering schemes for water management and debt recovery. The most advanced water metering technology being installed in low income communities is prepaid meters. Prepaid meters have a potential to fulfill all the range of objectives that municipalities install advanced metering technology for. This technology is found to have high maintenance requirements due to high failure rate. For successful implementation, it is important that municipalities have adequate budget for repairs and maintenance or seek technical support from manufacturers.
  • Thumbnail Image
    Item
    Open Access
    An evaluation of the pressure-leakage response of selected water distribution networks in South Africa
    (2019) Levin, Seamus Jay; Van Zyl, Jakobus E
    Pressure is one of the major factors influencing leakage in water distribution systems. For this reason, pressure management has become standard practice in reducing leakage in water distribution networks around the world. A range of N1 values have been published following studies of the impact of pressure management. Further studies have contributed towards the development of leakage parameters which represent physical properties of the pressure management system. This study aims to add to, and improve, the information on leakage parameters and their relationships.This study will seek to add to previously published data on the impact of pressure on leakage in field studies and determine the respective leakage parameters and identify relationships with respect to the latest findings on pressure and leakage behaviour. Significant research and investigations have been done at laboratory scale however theoretical developments have not been applied on field studies, and hence there is a lack of reports published in peer reviewed journals.The principal aims of this dissertation were to consolidate information from pressure management zones collected around South Africa and the analysis of results using a conventional methodology as well as alternative methodologies that used different pressure and flow inputs that represented the extreme range of pressure and flow.The relationships between the calculated leakage parameters were then studied and where leakage parameters were determined to be not physically possible, these were studied for errors.The dissertation is the result of research collected and conducted since February 2015 on 141 pressure management zones (PMZs) across South Africa.The data, collected from the field, consists of the zone characteristics, measurement data such as flow and pressure logging, and consumption data, including night time usage. From the 141 PMZs, only 107 were considered for this study due to exclusion of 34 PMZs for various reasons.From the analysed data, the significant results were that when using the conventional method (AZP as pressure input and QRL as flow input), 12% of head-area slope (m̄) values and 39% of initial leak area (Ā₀) values were negative. The calculated FAVAD N1 values ranged between -0.34 and2,20 (outliers were determined as N1=-31,88 and N1=6,77 but these are not impossible and can be explained through physical issues with the pressure management zone). The relationship between the calculated Leakage Exponent (N1) and the Leakage Number (LN) were determined to be consistent with theoretical studies. The Infrastructure Leakage Index (ILI) was determined for each PMZ for before and after pressure management and it was found that although leakage reduces with pressure management, the ILI is notalways reduced In fact, the ILI increased after pressure management for 39% of the PMZs. The relationships for the various leakage parameters were studied and illustrated. The only notable relationships revealed was that when N1 < 0,5 then m̄< 0 and when N1 > 1,5 then Ā₀< 0. Whilst this can be explained mathematically, a negative m̄ and Ā₀ are not physically possible. Therefore possible errors such as assumption errors and data errors were explored. For m̄, it was determined that four PMZs could not be explained from the correction of possible assumption or data errors. For Ā₀, it was determined that 11 PMZs could not be explained from the correction of possible assumption or data errors however the errors may be the result the presence of leaking/open boundary valves. The research undertaken is the first systematic study that is published where the parameters are explored to this extent in this detail, and using such a range of the latest conventional and the latest leakage theory. The result is that various pressure management zones can be analysed using standardised methodologies and calculations and these water distribution systems of different locations, sizes and characteristics can be compared and scrutinised. Furthermore, there are significant benefits of using the modified orifice equation which include determination of errors in assumptions or data collection or identifying the possibility of an open/leaking boundary valve. Finally, N1 values that fall outside of the typical range can often be explained by assessing the physical properties of the leakage parameters calculated from the modified orifice equation.
  • Thumbnail Image
    Item
    Open Access
    Case study review of advanced water metering applications in South Africa
    (2017) Ngabirano, Lillian; Van Zyl, Jakobus E
    Advanced water metering is part of a much larger movement towards smart networks and intelligent infrastructure. However, where advanced metering technology is focused more towards the need to obtain meter readings without human intervention in other parts of the world, in South Africa and other developing countries, advanced water metering (in the form of prepaid meters or water management devices) has been developing along a parallel path, driven by the need to provide services to previously unserved communities and deal with the problems caused by rapid urbanisation. In this report, conventional water metering is defined as systems using water meters that display their readings on the meters themselves and advanced water metering as systems that add additional components or functionality to a metering system. Advanced metering has the potential to provide substantial benefits if appropriately applied. However, compared with conventional metering, these systems are considerably more expensive and complicated, and often rely on technology that is still being developed. Advanced metering systems therefore carry a higher risk of failure, poor service delivery and financial losses unless the system is implemented with careful design and thorough planning. This report describes a number of case studies of the application of advanced metering in South Africa. The case studies were evaluated according to the evaluation framework described in Appendix A and their detailed evaluations are included in each relevant chapter. Evaluations were done in four areas: technical, environmental, social and economic. The technical evaluation is based on the systems complying with the relevant national metering standards and good metering practice, the environmental evaluations on battery disposal and water savings and the social evaluation on broad socio-economic indicators. It should be recognised that social issues are particularly complex and that no general evaluation framework can accurately predict whether an advanced metering system will be accepted by a particular community. The economic evaluations were based on reductions of the current system cost and not absolute values. Economic performance indicators included the effective surplus (income minus expenses over averaged over the meter service life) and capital repayment period. An overview of lessons learned and conclusions from the case studies are provided in Chapters 8 and 9 of the report.
  • Thumbnail Image
    Item
    Open Access
    An experimental investigation of leakage flow paths in soil surrounding leaks in water distribution systems
    (2017) Teeluckdharry, Sahil; Van Zyl, Jakobus E
    Over the last few decades, water stress has been imminent in most municipalities around the world. The problem of water losses from pipelines is a major concern due to the increasing demands. Leakage is normally responsible for a large percentage of water losses in distribution systems and results in enormous wastage of valuable resources and energy. Leaks may be developed in many forms and locations in the system and active leak detections are required to find and repair damaged pipes. Few studies have been done on the soil-leak interaction in real pipeline systems. Recent research have shown that the high velocity water jets entering the surrounding soil causes a fluidisation zone outside leaks. The fluidised zone of soil and water is responsible for dissipating most of the energy of the water jet from the pipe leak and thus, limiting the leak's ability to reach soil surface. In municipalities where active leak detections are not implemented, it is easier for municipalities to detect leaks if they appear on the surface and thus, it is crucial to understand the routes of water leaks and the factors causing them to appear above the ground. This study investigated the soil-leak interaction focusing mainly on factors affecting leakage flow paths in water distribution systems. An experimental set up was designed and built to study the different factors in a controlled environment. A series of experiments were performed where water jets from manufactured circular leaks were released in different trench set ups. Three main variables were investigated namely flow rate, leak orientation and in-situ soil to start understanding the movement of the leak flow as a preliminary study. The volumetric moisture content were measured using EC-5 moisture sensors at different locations in the tank to analyse the movement of leakage water and iPERLS smart water meters were used to measure the flow of water through the walls of the trench. The results of the experiments showed how much leakage water is actually lost through the side and bottom walls. The volumetric moisture content readings indicated the movement of the leak in the tank. The results of the study indicated that leak orientation has the greatest influence on the paths of the leaks. Also, the flow rate had to be increased to a very high value so that the leak appears above the sand surface. The permeability of the in-situ soil was found to have the least effect on the leakage flow paths.
  • Thumbnail Image
    Item
    Open Access
    Experimental investigation of leakage-induced pipe erosion outside of pipe leaks
    (2016) Pike, Stefan; Van Zyl, Jakobus E
    The problem of water loss from water distribution systems is an issue that faces municipalities worldwide. A large proportion of water loss is a result of leakage. With increasing water scarcity across the globe, it is imperative to conserve water resources, and hence reduce leakage in water distribution systems as best we can. Leaks develop in various different forms, and they form in pipes of all materials. It has been observed in numerous cases around the world that pipe material has been removed from the pipe surfaces adjacent to leaks in excavated failed water distribution pipe specimens. It was proposed by various researchers that this pipe material was being removed as a result of abrasive soil action caused by the pipe leak itself. When pressurised water distribution pipes fail, they emit high velocity jets of water into the surrounding soil bed. Research has shown that high velocity jets of water entering a granular soil bed have the ability to fluidise the bed, allowing the granular particles to move freely. This fluidisation mechanism is known as internal fluidisation. The concept of internal fluidisation offers an explanation for the erosion of pipe material adjacent to pipe leaks. In this study, the removal of pipe material adjacent to leaks due to internal fluidisation has been termed "leakage-induced pipe erosion." This phenomenon has received minimal attention from researchers in the past. Leakage-induced pipe erosion has the potential to aggravate small existing leaks. There are two main implications of aggravating small leaks; firstly, where water authorities do not utilise active leak detection programmes, aggravating the initial leak conditions of small leaks can result in increased long term water losses. Secondly, in water distribution systems where the water authority does implement active leak detection programmes, aggravating small leaks increases the probability of finding and repairing them. This aim of this study was to experimentally investigate the influence of various factors on the leakage-induced erosion process. Five main factors were investigated, namely bedding material grain size, cover depth, leakage flow rate, initial leak orientation and pipe material. An experimental setup was designed and manufactured in order to provide a controlled environment in which to investigate the factors affecting leakage-induced pipe erosion.
  • Thumbnail Image
    Item
    Open Access
    The feasibility of implementing advanced metering technology in high income areas in South Africa
    (2017) Mwangi, Mburu; Van Zyl, Jakobus E
    Water is an important natural resource and a building block to all life on earth. However, substantial increase in water demand and consumption has led to numerous nations, including South Africa, to face water scarcity. Improved water demand management strategies and water monitoring approaches are imperative. In South Africa, it's a legal requirement for all water supply points to be metered. Currently, water flow is primarily measured by conventional meters. However, substantial developments have been noted in the last two decades where conventional meters with added capabilities (such as communication capabilities) added have been introduced. These meters are known as advanced water meters. These capabilities offer functions such as leakage detection and more immediate consumption feedback. However, advanced meters also have significant disadvantages such as require high start-up capital and are susceptible to higher failure rates than conventional meters. It remains to be seen if advanced metering technology is an appropriate technology to be adopted in South Africa. Due to the different dynamics of South Africa's income level groups, the metering application and effects will differ for each income level group. Therefore, the purpose of this study is to investigate the feasibility of implementing advanced metering systems in high income areas in South Africa. An evaluation framework was developed to gauge the viability of implementing advanced metering systems on four performance criteria; technical, economic, environmental and social. The composite indicator framework template was selected as it was not tailor made for a specific reason and could be adapted for this research. The necessary framework input parameter data were acquired from practitioners in the field through questionnaires and from literature. Due to lack of advanced metering case studies in South Africa (except for prepaid meter), literature from developed countries were used as proxies. The input data entailed details of the current metering system, advanced metering system and new conventional metering system with the later used as a control for comparative purposes. The typical high-income scenario was derived from typical input data. For each input parameter, there were value ranges from the low parameter value to high parameter value. These ranges were used to conduct the sensitivity analysis on the framework to access critical input parameters to the success or failure of implementation Implementing advanced metering systems in high income areas in South Africa was found to be less economically viable than conventional meters. This is due to the lack of needed infrastructure for advanced metering as well as high initial capital costs and high operating costs. Advanced meters however proved to be more environmentally viable than conventional meters as they offered higher reduction in consumption. However, the manner in which faulty batteries are disposed could lead to environmental damage. Social factors were considered negligible for high income areas as revolts to introduction to new meters arises from financial constraints that those meters might induce. Further research with more South Africa based case studies and smaller scale advanced metering systems has been recommended.
  • Thumbnail Image
    Item
    Open Access
    A laboratory investigation of the effect of flow rate and bedding characteristics on the interaction of a vertical water jet with an idealised soil medium
    (2017) Govender, Kuveshan; Van Zyl, Jakobus E
    Water conveyed through pipes systems installed beneath the ground surface has become standard practice in which treated fresh water is transported to communities. This kind of water delivery is successful in many regards but also results in considerable amounts of water wastage in the form of undetectable leakage. This is a serious concern since fresh water reserves throughout the world are being depleted faster than it is replenished; yet, there exists a large gap in understanding how leaks outside water distribution pipes behave. Recent studies that have investigated external leakage behaviour have discovered that when water under pressure passes through a leak opening (orifice); a water jet is formed, which interacts with the surrounding soil (bedding material) in a manner that causes the granular medium to fluidise. This fluidisation process was seen to exhibit complex behaviour, which restricted shallow leaks under relatively high pipe pressures from growing and reaching the bed surface. As a result, leaks are able to remain bound beneath the ground surface with reduced chances of being detected and repaired. The goal of this study was to conduct experiments aimed of performing a sensitivity analysis on how leakage conditions in the bed are affected when soil-leak characteristics including jet flow rate, bed height and the size of the granular particles in the bed are varied. In this study a vertical water jet in an idealised granular bed (glass beads) was used. The leakage conditions that were examined for each soil-leak factor comprised of measuring the height of the fluidised region and distributions of pore pressure, fluid velocity and energy within the bed. The sensitivity analysis was based on data collected from experiments, which were conducted using an apparatus that was able to simulate an unbound pipe leak. The apparatus comprised of a glass tank, which housed the bedding material. An orifice installed at the bottom of the tank assisted in creating the water jet required for the pipe leak and, a Pitot tube positioning system above the tank allowed for positioning of straight and L-type Pitot tubes in the granular bed, which were used to measure the leakage conditions within the bed. Results from the experiments revealed that the soil-leak factors, which were investigated had significantly affected leakage conditions, each to varying degrees. Larger jet flow rates led to an exponential increase in fluidisation height and higher maximum pore pressures, velocities and energies were measured in the bed. It was found that by varying the bed height, fluidisation height increased linearly with decreasing bed height and only the pore pressure distribution was considerably affected, where larger maximum pore pressures were measured in beds that were shallower. The effects of varying particle size included lower fluidisation heights and maximum pore pressures in beds that contained larger particles. Interestingly, the velocity and energy distribution remained substantially unaffected.
  • Thumbnail Image
    Item
    Open Access
    Optimal reliability-based design of bulk water supply infrastructure-incorporating pumping systems
    (2015) Papathanasiou, Michael; Van Zyl, Jakobus E
    The optimal design of a bulk water supply system is centered on two major objectives: cost efficiency and the formation of a design solution that is appropriate for the conditions in which the system is to be implemented. The currently employed CSIR (2000) design guidelines utilise deterministic measures to size system components. The efficiency of following a deterministic approach to bulk water system design, involving pumping systems, was investigated. This was seen as necessary owing to the vast spectrum of influences and the interrelation of parameters that constitute a bulk water supply system. A model developed by Chang & van Zyl (2012) sought to address this inefficiency by optimizing a bulk water supply system, with the core objectives of cost and reliability. The determination of these objectives was achieved by using a capital cost model for cost determination and a stochastic model developed by Van Zyl et al. (2008) for reliability. While this produced workable results, the application was relatively limited, and applied only to non-pumped, gravity-fed flow. As such, the failure mechanisms of the supply system did not include the effects of pump failure, an important influence on overall system reliability. In addition, the costing system was based solely on capital cost and did not take into account the life-cycle cost involved with the implementation of a bulk water supply system. The investigation sought to expand the applicability of the model through the incorporation of pumping systems and life-cycle costing. It was further intended to compare the expanded model to both the model developed by Chang & van Zyl (2012) and the CSIR (2000) guidelines. A sensitivity analysis would also be performed.
  • Thumbnail Image
    Item
    Open Access
    Optimal reliability-based design of bulk water supply systems
    (2011) Chang, Ching-Chiao; Van Zyl, Jakobus E
    Bulk water supply systems are usually designed according to deterministic design guidelines. In South Africa, design guidelines specify that a bulk storage reservoir should have a storage capacity of 48 hours of annual average daily demand (AADD), and the feeder pipe a capacity of 1.5 times AADD (CSIR, 2000). Nel & Haarhoff (1996) proposed a stochastic analysis method that allowed the reliability of a reservoir to be estimated based on a Monte Carlo analysis of consumer demand, fire water demand and pipe failures. Van Zyl et al. (2008) developed this method further and proposed a design criterion of one failure in ten years under seasonal peak conditions. In this study, a method for the optimal design of bulk water supply systems is proposed with the design variables being the configuration of the feeder pipe system, the feeder pipe diameters (i.e. capacity), and the size of the bulk storage reservoir. The stochastic analysis method is applied to determine a trade-off curve between system cost and reliability, from which the designer can select a suitable solution. Optimisation of the bulk system was performed using the multi-objective genetic algorithm, NSGA-II. As Monte Carlo sampling can be computationally expensive, especially when large numbers of simulations are required in an optimisation exercise, a compression heuristic was implemented and refined to reduce the computational effort required of the stochastic simulation. Use of the compression heuristic instead of full Monte Carlo simulation in the reliability analysis achieved computational time savings of around 75% for the optimisation of a typical system. Application of the optimisation model showed that it was able to successfully produce a set of Pareto-optimal solutions ranging from low reliability, low cost solutions to high reliability, high cost solutions. The proposed method was first applied to a typical system, resulting in an optimal reservoir size of approximately 22 h AADD and feeder pipe capacity of 2 times AADD. This solution achieved 9% savings in total system cost compared to the South African design guidelines. In addition, the optimal solution proved to have better reliability that one designed according to South African guidelines. A sensitivity analysis demonstrated the effects of changing various system and stochastic parameters from typical to low and high values. The sensitivity results revealed that the length of the feeder pipe system has the greatest impact on both the cost and reliability of the bulk system. It was also found that a single feeder pipe is optimal in most cases, and that parallel feeder pipes are only optimal for short feeder pipe lengths. The optimisation model is capable of narrowing down the search region to a handful of possible design solutions, and can thus be used by the engineer as a tool to assist with the design of the final system.
  • Thumbnail Image
    Item
    Open Access
    Predicting variations in the areas of circular leaks in water pipes due to changes in pressure
    (2016) Nsanzubuhoro, Rene Mathias Nsanzintore; Van Zyl, Jakobus E; Zingoni, Alphose
    Leak openings in water distribution system pipes are not static, but have areas that vary with pressure. These changes in area affect the way that leakage respond to changes in pressure, and was thus important for municipal engineers to understand. This study focussed on round hole leak openings that can exist as pipe failures. In this study, a finite element analysis (FEA) study was carried out to model the behaviour of round holes in pipes with varying pressure under elastic conditions. It was found that the areas of the holes vary as linear functions of pressure in the pipe. The slope of this linear function, also referred to as the head-area slope m, was identified as a critical element to investigate because this head-area slope essentially gives an indication of the extent to which the leak area is sensitive to pressure. The FEA was then used to better understand the factors that affect the head-area slope m. In order to understand which parameters affect the head-area slope m, a parametric study was conducted. This parametric study was done by varying each parameter in turn to study the effect of that parameter on the head-area slope of the pipe. The parameters investigated in the study include the pipe material (elastic modulus, Poisson's ratio and longitudinal stress), pipe geometry (wall thickness and internal diameter) and hole diameter. It was found in this study that of the five aforementioned geometric and material parameters, the elastic modulus, wall thickness and internal diameter had the most significant effect on the head-area slope m. The extent to which these parameters influenced m depended on the hole diameter. It was found that as the hole diameter increased the effect of the parameter was more significant. Solid mechanics theory was then used to develop an equation to predict the head-area slope of round holes in different pipes and materials. Various techniques were used in the development of the equation. To calibrate and validate this equation the head-area slopes calculated from the equation were compared and plotted against the finite element head-area slopes. A reasonable expression was found that can be used in further research and practice. The head-area slopes m obtained from this equation was compared to the head-area slopes m obtained in the FEA analysis. It was found that this expression predicts the finite element model analysis reasonably well, producing trends that are similar to those found from the finite element models.
  • Thumbnail Image
    Item
    Open Access
    Realistic modelling of leakage in water distribution pipe networks
    (2018) Kabaasha, Asaph Mercy; Van Zyl, Jakobus E
    Several experimental and modelling studies have established that leak areas are mostly not fixed but vary linearly with pressure. Introducing this linear relationship into the orifice equation, results in a two-part modified orifice equation for leakage modelling with pressure head exponents of 0.5 and 1.5 respectively. Current hydraulic network solvers apply the conventional power leakage equation to model pressure dependent demands such as leakage. The empirically derived power leakage equation does not explicitly consider the leak area variation with pressure and it has been found to be flawed under certain conditions. The aim of this study therefore, was to incorporate the modified orifice equation into the algorithm of a hydraulic network solver and evaluate the impact this has on leakage modelling. Epanet is the hydraulic modelling software whose algorithm of the network solver was modified. In addition, a stochastic model for network leak generation and distribution was developed. The conventional and the modified software were applied to different levels of stochastically generated and distributed leakage in three differently sized pipe networks. It was found that the conventional power leakage equation results in significant leakage volume and flow rate errors under certain conditions. A methodology was also developed to correct the conventional power leakage equation so that it can be used to model leakage realistically without a change of the software to one that uses the modified orifice equation. The methodology was thereafter applied to an existing model that detects leaks in standard water distribution pipe networks, and the results showed significant improvements in the performance of the model.