Urban Water Distribution Networks

Assessing Systems Vulnerabilities, Failures, and Risks

Symeon Christodoulou, Michalis Fragiadakis, Agathoklis Agathokleous, Savvas Xanthos

• Publisher: Butterworth-Heinemann
• Year: 2017
• Print ISBN: 9780128136522
• eBook ISBN: 9780128136539
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

Urban Water Distribution Networks: Assessing Systems Vulnerabilities and Risks provides a methodology for a system-wide assessment of water distribution networks (WDN) based on component analysis, network topology and, most importantly, the effects of a network's past performance on its seismic and/or non-seismic reliability. Water distribution networks engineers and system designers face multiple operational issues in delivering safe and clean potable water to their customers.- Includes vulnerability assessment methods for water distribution pipes- Discusses topological aspects and their effects on network vulnerability- Explores analytical and numerical modeling methods for finding and analyzing systems vulnerabilities in water distribution networks- Features real world case studies of networks under continuous and intermittent water supply operations

Chapter 1

Introduction

Classical risk analysis is principally concerned with investigating the risks surrounding a plant (or some other object), its design and operations. Such analysis tends to focus on causes and the direct consequences for the studied object. Vulnerability analysis, on the other hand, focuses both on consequences for the object itself and on primary and secondary consequences for the surrounding environment. It also concerns itself with the possibilities of reducing such consequences and of improving the capacity to manage future incidents.

Lövkvist-Andersen, A.L., et al. (2004), Conference of the Society for Risk Analysis.

Abstract

Water distribution networks and, in general, lifeline systems are of critical importance to the uninterrupted provision of services and thus to the resiliency of a city. Lifeline systems share the attributes of being distributed systems, rather than isolated facilities, providing products or services that are transferred through networks that often cross legal and jurisdictional boundaries. In effect, lifelines are the infrastructure systems that support urban life and because of their interconnected nature, once a lifeline system is damaged by an earthquake or other natural hazard, other lifeline systems (or infrastructure components) may malfunction as well. The term “resilience” refers to a system's (or city's) capacity to quickly and effectively recover from a catastrophic event.

Keywords

Water distribution networks (WDN); Vulnerability; Normal operating conditions; Abnormal operating conditions

1.1 Introduction

Each year, hundreds of kilometers of pipes across the globe are repaired or replaced in an attempt to mitigate the effects of pipe bursts and of water loss, and to maintain the uninterrupted transport of water. Existing water distribution systems are increasingly at risk due to numerous factors (both internal and external to the distribution networks) and the accidental or deterioration-based breakage of urban water distribution networks (WDN). This situation represents a significant problem for communities and authorities.

Water distribution networks deliver water from its sources to the customers of the network. Being able to assess the reliability of the network against different hazards helps water distribution agencies prioritize their interventions and ensure a minimum reliability level of the network. Therefore, water distribution agencies are required to develop and implement new methods for monitoring, repairing (or replacing) aging WDN infrastructures, as well as modeling deteriorating WDN conditions, and proactively devising strategies to keep the networks in operation. In essence, water distribution agencies are faced with the increasingly more complex task of intelligently and efficiently assessing (or modeling) the condition of a pipe network, while managing the network in ways that maximize its reliability and minimize its operational and management costs. The question that usually arises is whether an organization should repair or replace deteriorating water mains and, in either case, what should be the sequence of any such repairs as part of a long-term network rehabilitation strategy.

Research to-date has helped identify a number of potential time-invariant and time-dependent risk factors contributing to pipe breaks and to WDN vulnerability. Among them are factors such as a pipe's age, diameter, material, and number of previous breaks, as well as the network's operating pressure and water flow. Component-based risk assessment, though, is only one of the many dimensions pertaining to the general problem of assessing the reliability of WDNs. Network topology and hydraulic operations are also of significant impact to WDNs, whilst abnormal operations (such as seismic loads) are also risk-of-failure sources that need to be considered (Fig. 1.1).

Figure 1.1 Water distribution network vulnerability analysis (schematic).

Granted that risk assessment of critical infrastructure poses a major problem for the engineering community, the problem is even more challenging when it comes to underground infrastructure and “lifelines”, such as the urban water distribution networks. The challenges arise from a number of sources: (i) the system reliability depends on both the network topology and the reliability of the system's constituent components; (ii) WDNs consist of various system components of variable design parameters; (iii) there is a lack of historical data on the components' performance over time and under varying operating/loading conditions; and (iv) the networks are vastly inaccessible for visual inspections.

WDN vulnerability, though, is not static. Not only is it the product of many time-invariant and time-variant factors, but it is itself also dynamic in nature. A WDN performs one way under normal operations and another way under abnormal operating conditions. Abnormal operating conditions may be the result of seismic loadings, the implementation of intermittent water supply policies, or simply the scheduled (or unscheduled) maintenance operations in the WDN.

For example, recent cases of WDNs subjected to intermittent water supply operations have documented the adverse effects of such policies on the vulnerability of the networks, while recent earthquakes have shown that following a strong earthquake the caused damage of the various urban lifelines may cause a series of immediate, short-term, and long-term problems.

1.2 Why the Need for Vulnerability Assessment of Water Distribution Networks?

A water distribution network is, in a way, a “living organism” with several of its components being constantly in flux, subjected to internal and external forces of time-variant and invariant parameters, and which with every component failure its survival as a whole is affected. After all, as it will be discussed in Chapter 2 (p. 21), WDNs don't differ much from living organisms for which every past failure incident (“illness”) brings them closer to catastrophic failure (“death”). Hence why survival analysis (a method stemming from biological sciences and which attributes pipelines with characteristics similar to those of patients) is among the most common methods for assessing the probability of failure of water pipelines, and why one needs to constantly assess the fragility of a network's components and with that the vulnerability of the network as a whole.

The need for vulnerability analysis is further compounded by the importance of WDNs in our lives, as they constitute one of the primary “lifeline networks” of modern urban societies. Granted their importance to society, it is thus imperative to develop knowledge and to device methods for continuously and accurately assessing their state of affairs and their vulnerability under both normal and abnormal operating conditions.

Furthermore, WDN vulnerability relates to water quality and the risks to the consumers' health, as natural or malicious threats to the WDN threaten the health and well-being of the citizens that the WDN serves. Pipe deterioration leads to pipe breakages, breakages lead to water loss and to infiltration of pathogens in the network, pathogens lead to water contamination, contamination leads to health threats for the population being serviced by the WDN.

Finally, WDN vulnerability is associated with the disruption of residential, commercial and industrial activities and the cause of severe direct and indirect economic losses which, in the case of indirect losses, are higher the more developed the society is. Direct losses relate to the cost of repair, while indirect losses relate to the way the economy is affected by the disruption of the lifeline.

1.3 Current Operations & Management Practices for Water Distribution Networks

The globalization of the problem of diminishing water resources has increased the level of interest in it, and inspired a lot of scientific research on the topic. The range of research topics related to potable water resources is vast, among which prominent are the topics pertaining to the sustainable management of WDNs. In its general definition, sustainability relates to the ability to endure and sustainable development refers to development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Within the WDN domain, sustainable management is defined as the application of practices for the operation and management of WDNs in ways that allow the networks to thrive while benefiting both current and future generations, and while limiting the depletion of water resources.

However, the biggest problem currently faced worldwide by the managing authorities of water supply networks is that most of the pipe networks have already reached their useful life and that, as a result, most WDNs need maintenance, repair or even replacement to a great extent. In fact, the daily volume of water lost in such networks is enormous and, as a result, this reality has brought to the foreground the need for improved operations and maintenance (O&M) actions and for the development of leakage management plans/actions for numerous scenarios [55].

As aforementioned, in recent years the problem of water resources' shortage (especially the shortage of potable water) has grown and has expanded beyond the boundaries of countries where water shortage is traditionally encountered. As a result, national research has grown to international collaboration and joined research agendas, to the exchange of knowledge and to the development of good-practice guidelines in the form of manuals issued by national and international water-related organizations which, in turn, have subsequently been promoted to the various entities responsible for the management of the WDNs. The developed manuals primarily focus on the proper restructuring of WDNs for the improvement of their performance, on the efficiency of operations and the increased effectiveness in leakages detection, on fiscal improvements and on the development of decision support system tools for the sustainable management of WDNs [96,120,126,155].

1.3.1 Management Model Proposed by the International Water Association (IWA)

In 1999, the International Water Supply Association (IWSA) and the Internation...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Figures
• List of Tables
• About the Authors
• Preface
• Acknowledgments
• Book Organization
• List of Acronyms
• Chapter 1: Introduction
• Chapter 2: Vulnerability Assessment of Water Distribution Networks Under Normal (Continuous Water Supply, CWS) Operating Conditions and Nonseismic Loads
• Chapter 3: Vulnerability Assessment of Water Distribution Networks Under Abnormal Operating Conditions and Nonseismic Loads – The Case of Intermittent Water Supply (IWS)
• Chapter 4: Topological Vulnerability
• Chapter 5: Vulnerability Assessment of Water Distribution Networks Under Seismic Loads
• Chapter 6: Hydraulic Vulnerability Assessment of Water Distribution Networks
• Chapter 7: Real-Time Monitoring
• Chapter 8: From Historical and Seismic Performance to City-Wide Risk Maps
• Chapter 9: Disaster Resilience of Water Distribution Networks
• Epilogue
• Bibliography
• Index