Jakobus Ernst Van Zyl

Jakobus Ernst Van Zyl
University of Auckland · Department of Civil and Environmental Engineering

Ph.D.

About

194
Publications
64,676
Reads
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2,240
Citations

Publications

Publications (194)
Article
Full-text available
The hydraulics of leakage and intrusion flows through leak openings in pipes is complicated by variations in the leak areas owing to changes in pressure. This paper argues that the pressure–area relationship can reasonably be assumed to be a linear function, and a modified orifice equation is proposed for more realistic modeling of leakage and intr...
Article
Full-text available
This study investigated the feasibility of characterising the pressure-leakage response of water distribution systems using the FAVAD (Fixed and Variable Area Discharges) equation, instead of the conventional N1 power equation. The study was based on 300 network models with randomly distributed leaks and 35 networks generated through a sensitivity...
Article
Full-text available
It has been well established that leakage from pipes is more sensitive to changes in pressure than the square root relationship predicted by the orifice equation. The main reason for this is that leak areas are not static, but vary with changes in system pressure. While previous studies have shown that the leak area is a linear function of pressure...
Article
Full-text available
In this study, the relationship between the conventional power equation and the FAVAD (Fixed and Variable Area Discharges) equation for modelling leakage as a function of pressure was investigated. It is shown that different leakage exponent (or N1) values are obtained for the same leak when measured at different pressures. An analytical exploratio...
Conference Paper
Full-text available
The public domain EPANET software developed by Dr. Lewis Rossman (2000) has become the standard tool for water distribution systems research, and its hydraulics engine is used by many commercial modeling packages. In his WDSA 2009 keynote address at the EWRI Congress in Kansas City, Dr. Rossman proposed an open source model for EPANET. Such an open...
Article
Full-text available
This paper reviews three digitalisation projects in the Building Innovation Partnership, an industry-led research and innovation initiative based at the University of Canterbury, New Zealand, focussed on improving the transfer of infrastructure information within and between organisations. The BIM to BAM project focuses on the use of client-facing...
Article
A pipe condition assessment device (PCAD) was developed to detect, characterise leakage and assess the condition of water distribution networks (WDN). In this study, the reliability and repeatability of the device results were established by first characterising known leak types on pipe sections using a standardised method. Then, three manufactured...
Article
The COVID-19 pandemic affected the operation of water utilities across the world. In the context of utilities, new protocols wereneeded to ensure that employees can work safely, and that water service is not interrupted. This study reports on how the operations of 27 waterutilities worldwide were affected by the COVID-19 pandemic. Interviews were c...
Article
Sewer pipe deterioration is driven by a finite number of root causes and processes. Thus, it should be both feasible and advantageous to have a uniform classification system that can be universally applied in sewer deterioration modeling and asset management. However, a literature review of existing classification systems revealed several problems...
Article
Urban water systems can be highly energy intensive. Yet, they are also excellent candidates for demand-response since they possess readily controllable operations and large amounts of storage. However, real-worlds trials have delivered mixed results, which implies the need to understand the underlying mechanisms of flexibility in water operations....
Article
Full-text available
Theoretical and experimental results for the evolution of cavities generated by upward vertical leakage jets in porous media are presented. The formulation is based on the conservation principles of mass, momentum, and energy. Two conditions were considered: two-dimensional isotropic medium and three-dimensional isotropic medium. The results of the...
Article
Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.
Article
Fluid pressure influences leakage flow rate in water distribution pipe networks. Significant progress has been made in the use of pressure management techniques to control leakage. An empirical power equation (known as the N1 power equation) is widely used to model the pressure–leakage relationship in practice. However, recent research has shown th...
Article
A novel pressure-based leakage assessment and characterisation method was applied to a range of bulk pipelines in the field to evaluate the practical application of the method. With this method, the testing equipment, which consists of a variable speed pump unit, a water tank and measuring equipment, all mounted on a trailer, was connected to a bul...
Article
Full-text available
This paper reports on an experimental study on the scouring of pipe materials on the outside of leaks caused by soil fluidization. A base experiment was designed consisting of a 3 mm diameter hole angled at 45° to the horizontal in a 110 mm diameter unplasticized polyvinyl chloride (uPVC) pipe. Five parameters were investigated in a sensitivity ana...
Article
Full-text available
It has been well established in several experimental and modeling studies that leak areas are often not fixed, but vary as linear functions of pressure. Replacing this linear equation into the orifice equation results in a two-part modified orifice leakage equation with head exponents of 0.5 and 1.5. The purpose of this study was to incorporate the...
Article
Full-text available
Leak openings in water distribution system pipes are not static, but vary with pressure. These changes in area affect the way that leaks respond to changes in pressure, and are thus important for municipal engineers to understand. In this study, the behavior of round holes in pressurized pipes was investigated using finite element analysis (FEA), u...
Article
Full-text available
Much progress has been made over the last decade in understanding the behaviour of flow through leak openings with changes in water mains pressure. In particular it has been established that variations in leak areas with pressure is the main factor responsible for the range of leakage exponents observed in practice, and several numerical and experi...
Article
Full-text available
Estimation of annual average water demand figures is critical for the design and evaluation of water distribution systems. This study evaluated the metered water consumption of more than 67,000 non-domestic consumers in six categories from cities and towns in South Africa. It was found that lognormal distributions provide good descriptions of the a...
Conference Paper
Research has shown that area of leak openings varies linearly with pressure under both elastic and viscoelastic conditions. However, hydraulic modelling of water distribution systems currently uses a power function that does not explicitly take into account leak area variation with pressure. This function is commonly known as the N1 power equation....
Conference Paper
Full-text available
This paper presents an experimental study on internal fluidisation which can occur in the soil outside of a leak in a buried water distribution pipe. The study proposes an experimental method of measuring excess pore pressure and flow velocity in an uniform glass beads medium surrounding the leak. One flow rate of 2 l/min at a fixed leak diameter o...
Article
Full-text available
This study investigated the extent of apparent losses due to water meter under-registration in South Africa. This was done by first estimating the under-registration of new meters due to on-site leakage, and then the additional under-registration due to meter aging. The extent and flow distributions of on-site leakage were determined through field...
Data
The Richmond water distribution system was used in a PhD research project on operational optimization of water distribution systems by Jakobus E (Kobus) van Zyl (2,3) at the University of Exeter in 2001. This file contains the input files and best solution found. It provides supplementary data to the following documents: - Van Zyl, J.E., Savic,...
Conference Paper
It has been well established that leakage from pipes is more sensitive to changes in pressure than the square root relationship predicted by the orifice equation. The main reason for this is that leak areas are not static, but vary with changes in pressure. While previous studies have shown that the leak area is a linear function of pressure for el...
Article
Full-text available
In this study, the relationship between the conventional power equation and the FAVAD (Fixed and Variable Discharges) equation for modelling leakage as a function of pressure is investigated. It is shown that different leakage exponent (or N1) values are obtained for the same leak when measured at different pressures. Analytical exploration of the...
Article
Full-text available
The purpose of this paper is to summarize the latest theoretical developments on the pressure-leakage relationship in water distribution systems. It is clear that the high leakage exponents often found in field studies are mainly caused by leak areas varying with system pressure, and a good understanding of the response of leaks deforming elastical...
Article
Full-text available
Pressure is one of factors influencing leakage in water networks [1] and [2]. In this study, the FAVAD concept and leakage number were analysed for a number of real water network pressure management zones in the KwaDabeka Township in KwaZulu-Natal, South Africa Pressure-leakage parameters were determined for each pressure management zone. Results s...
Article
Full-text available
Previous experimental and numerical studies have shown that leaks in water distribution systems expand linearly with pressure under elastic conditions. The flow rate from such leaks as a function of the pressure head is described by FAVAD equation. The aim of this study was to investigate whether a combination of individual leaks displaying FAVAD b...
Article
Full-text available
Pressure management has been used for more than 3 decades to reduce leakage from water distribution systems. While few of these studies have been published, information on the ranges of field study leakage exponents is available. In contrast, several studies on the pressure-leakage relationship of individual leaks have been published, and verified...
Article
Full-text available
The standard formulation of the hydraulic network equations incorporates a power function for modeling pressure-dependent consumption such as leakage. However, recent research has shown that the FAVAD leakage model more accurately accounts for the behavior of leaks in practice. The objective of this paper is to propose a method for solving the hydr...
Article
Full-text available
Rapid growth in population, urbanization, agriculture, industrial development and natural occurrences like drought, has increased the demand for water resources in South Africa. Hence, the use of two separate pipe systems to convey water of different qualities to meet domestic, industrial, institutional and agricultural requirements for potable and...
Article
Full-text available
Control valves are commonly used for the operation of water distribution systems. Modeling these devices typically requires that their operating states are known, or that a computationally expensive search is undertaken over all possible operating states. This paper presents a novel method of modeling control valves (including flow control, pressur...
Article
Full-text available
It is possible to analyse the reliability of municipal storage tanks through stochastic analysis, in which the user demand, fire water demand and pipe failures are simulated using Monte Carlo analysis. While this technique could in principle be used to find the optimal size of a municipal storage tank, in practice the high computational cost of sto...
Article
Full-text available
Water reuse projects can fail if the factors (social, technical, financial, etc) governing their implementation are not adequately addressed prior to implementation. This paper presents the findings of the analysis of questionnaires administered to potential domestic and nondomestic consumers in Capricorn and Vhembe (Limpopo Province) where wastewa...
Article
Full-text available
This study investigated factors affecting the average domestic water demand of a large number of suburbs in South Africa. Suburbs form an ideal demand grouping since they tend to have similar stand areas, climatic conditions and user characteristics. In addition, since properties within a suburb are close to one another, it may be reasonably assume...
Article
Full-text available
This paper describes a collaborative process of identifying and prioritising current and future water research questions from a wide range of water specialists within South Africa. Over 1 600 questions were collected, reduced in number and prioritised by specialists working in water research and practice. A total of 59 questions were finally propos...
Article
Full-text available
The hydraulic reliability of bulk water-supply systems can be defined in terms of the failure frequency of the municipal storage tanks they supply: the system fails when the tank runs dry and is functional otherwise. Municipal storage tanks are normally sized according to deterministic guidelines that make allowances for balancing, fire and emergen...
Article
Full-text available
Pressure has a major impact on the rate of leakage from leak openings in pipes and studies have shown that the leakage exponents in networks can be substantially larger than the theoretical orifice exponent of 0.5. The most important reason for this behaviour is that leak areas are not fixed, but increase as a function of pressure. In this study, f...
Article
Full-text available
This paper reports on a preliminary study carried out to investigate the effect of soil, and particularly fluidisation of soil, around leaking water pipes. During the study a bed of particles is fluidised at controlled flow rates, using upward-pointing orifices to simulate holes in a pipe. The extent of the fluidised zone and the head drop within t...
Article
Full-text available
Wastewater reuse is increasingly becoming an important component of water resources management in many countries. Planning of a sustainable wastewater reuse project involves multi-criteria that incorporate technical, economic, environmental and social attributes. These attributes of sustainability is the framework upon which the decision support to...
Article
Full-text available
Treated wastewater represents a significant potential source of reclaimed water for some beneficial reuses. However, public concern over the risks/health-related hazards of wastewater reuse has limited the general acceptability of reuse systems in many countries. It is important to manage the operation of recycled water systems in such a way that i...
Conference Paper
More and more water utilities are using hydraulic software solutions to predict the working of their water distribution network. Simulating pressure control valve in the steady state context, because of the unknown status of the valve, may cause a problem of convergence or even lead to unrealistic results. The objective of this paper is to present...