Magnus Moglia

A physical probabilistic model to predict failure rates in buried PVC pipelines

For older water pipeline materials such as cast iron and asbestos cement, future pipe failure rates can be extrapolated from large volumes of existing historical failure data held by water utilities. However, for newer pipeline materials such as polyvinyl chloride (PVC), only limited failure data exists and confident forecasts of future pipe failures cannot be made from historical data alone. To solve this problem, this paper presents a physical probabilistic model, which has been developed to estimate failure rates in buried PVC pipelines as they age. The model assumes that under in-service operating conditions, crack initiation can occur from inherent defects located in the pipe wall. Linear elastic fracture mechanics theory is used to predict the time to brittle fracture for pipes with internal defects subjected to combined internal pressure and soil deflection loading together with through-wall residual stress. To include uncertainty in the failure process, inherent defect size is treated as a stochastic variable, and modelled with an appropriate probability distribution. Microscopic examination of fracture surfaces from field failures in Australian PVC pipes suggests that the 2-parameter Weibull distribution can be applied. Monte Carlo simulation is then used to estimate lifetime probability distributions for pipes with internal defects, subjected to typical operating conditions. As with inherent defect size, the 2-parameter Weibull distribution is shown to be appropriate to model uncertainty in predicted pipe lifetime. The Weibull hazard function for pipe lifetime is then used to estimate the expected failure rate (per pipe length/per year) as a function of pipe age. To validate the model, predicted failure rates are compared to aggregated failure data from 17 UK water utilities obtained from the United Kingdom Water Industry Research (UKWIR) National Mains Failure Database. In the absence of actual operating pressure data in the UKWIR database, typical values from Australian water utilities were assumed to apply. While the physical probabilistic failure model shows good agreement with data recorded by UK water utilities, actual operating pressures from the UK is required to complete the model validation.

Strong exploration of a cast iron pipe failure model

A physical probabilistic failure model for buried cast iron pipes is described, which is based on the fracture mechanics of the pipe failure process. Such a model is useful in the asset management of buried pipelines. The model is then applied within a Monte-Carlo simulation framework after adding stochasticity to input variables. Historical failure rates are calculated based on a database of 81,595 pipes and their recorded failures, and model parameters are chosen to provide the best fit between historical and predicted failure rates. This provides an estimated corrosion rate distribution, which agrees well with experimental results. The first model design was chosen in a deliberate simplistic fashion in order to allow for further strong exploration of model assumptions. Therefore, first runs of the initial model resulted in a poor quantitative and qualitative fit in regards to failure rates. However, by exploring natural additional assumptions such as relating to stochastic loads, a number of assumptions were chosen which improved the model to a stage where an acceptable fit was achieved. The model bridges the gap between micro- and macro-level, and this is the novelty in the approach. In this model, data can be used both from the macro-level in terms of failure rates, as well as from the micro-level such as in terms of corrosion rates.

Modelling an urban water system on the edge of chaos

Viewing an urban water system as a complex adaptive system provides new opportunities for analysis and avoids some critical simplifications. Taking this perspective, it is possible to explore the inter-related effects of changes to the system. This is particularly important in the developing world where donors providing aid aim to improve conditions but struggle to understand and quantify the systemic impacts of their actions. This is because an intervention aiming to improve condition may also have unintended and undesirable effects. To provide decision support, this paper describes an agent-based model of an urban water system, developed on the basis of ethnographic interviews, and subsequently evaluated by local stakeholders. The paper describes the model design as well as the results of scenarios. The model provides guidance on which system amendments may produce the best outcomes in terms of output variables, and on the basis of sense-checking and sensitivity analysis it is judged that model results are likely to give a good indication about possible real world outcomes. It is clear that no single strategy will solve all problems on its own, but that a combined strategy - with a strong focus on groundwater management and protection - is likely to be most successful.

Sewer Performance Reporting: Factors That Influence Blockages

Managing sewer blockages represents a significant operational challenge for water utilities. In Australia, company-level blockage rates are used to compare the effectiveness of the management strategies of different utilities. Anecdotal evidence suggests that this basis may not be a fair one for comparison because blockages are influenced by a range of factors beyond management control and vary from company to company. This issue was investigated as part of a broader research effort on sewer-blockage management undertaken in conjunction with the Water Services Association of Australia (WSAA) and its members. A Web-based survey was used to collate expert opinion on factors that influence blockage rate. The identified factors were then investigated in an exploratory analysis of blockage-related data provided by two participating utilities, supported by literature reviews. The results indicate that blockage rate is influenced by a range of factors, including asset attributes, climatic conditions, water consumption, and soil type. Because these factors vary from utility to utility, this research supports the finding that company-level blockage rate in itself is not an appropriate metric for comparing management effectiveness.

Assessing the likelihood of realizing idealized goals: The case of urban water strategies

Urban water management can be challenging, but in Small Island Developing States it is particularly difficult due to resource constraints and isolation. This is the situation in the town of Tarawa in Kiribati, where attempts to improve water services have often not led to the desired outcomes. The reasons are varied, and include widely a lack of consideration of local circumstances, process requirements, and inadequate involvement of affected stakeholders, and inadequate cross-sectoral coordination. In light of the tendency in urban water planning to assume only the idealized performance of strategies, the authors argue that there is a need to also formally consider the likelihood of realizing this idealized performance. It is difficult to assess such likelihoods, other than via the use of judgments by expert and local stakeholders. Such judgments are typically qualitative and fairly abstract and often not directly concerning a particular strategy. The current paper provides a methodology to assess the likelihood of the idealized performance of strategies, based on Bayesian Networks (BNs) and Subjective Logic (SL) utilizing expert and local knowledge, creating a capacity to capture and apply previous experiences, and dispersed knowledge in decision making and planning. The methodology has been developed and tested on water management strategies in the town of Tarawa, Kiribati. As such, this paper provides a method for mapping the causal explanations for why developments do not achieve their set goals, and the approach may form the basis for assessments to be more widely applied when evaluating urban water strategies in similar contexts. In this paper, the approach has been applied by using existing data from interviews and literature to evaluate one strategy, reserve extensions and groundwater extraction. Other strategies, i.e. rainwater harvesting, desalination and have also been evaluated but have not been described in this paper because of limited space.

Water use, sanitation and health in a fragmented urban water system: case study and household survey

In a study to identify strategies to deal with rapid urbanization and threatening climate change, in Can Tho City, Vietnam, a survey of 1200 households was undertaken to investigate water access and sanitation services. The survey targeted three different groups based on their access to water services: (a) those with piped water supply, (b) without piped water, and (c) a mix of (a) and (b). Socio-economic factors and level of urbanization significantly influenced the different water sources accessed by households and their type of sanitation. Results indicated that householders often employed multiple water sources in an attempt to match source with intended use. The use of multiple water sources, levels of sanitation and the quality of water were found to be good indicators of reported rates of illness. Results also showed that the provision of piped water does not always provide the desired health outcomes, as the definition of adequate water supply does not include water quality objectives. Therefore, more detailed assessments may be required to understand how people use and access water and sanitation, and the impacts on public health.

Vulnerability of water services in Pacific Island countries: combining methodologies and judgment

Water services in Pacific Island Countries are particularly vulnerable due to a range of circumstances such as the scale of operation, remoteness of location, financial constraints, cultural complexity and the ability to access technical and other capacity by their administrations. Additionally, the authors argue that comparative assessment of water needs for differing locations is fraught with difficulty because of the combination of systemic complexity, diversity of situations and lack of suitable, consistent and objective data. In these challenging situations, a method for assessment of the vulnerability of water services has been developed on the basis of knowledge and experiences of water professionals, elicited using a structured group interaction known as a Delphi survey. The Delphi survey has been undertaken with a range of stakeholders including panels of experts, funding agencies and local decision makers. Through the Delphi process, key factors contributing to vulnerability have been identified and the output has been used to develop an index methodology. Such an index methodology, similar to the Climate Vulnerability Index, has a number of dimensions, variables and appropriate weights expressed within a set of equations. Given quantification of variables, this method can be used to assess the relative vulnerability of water services in Pacific Island Countries. The method used to develop this index could also be applied to other contexts where appropriate.

Sustainable urban systems: Co-design and framing for transformation

Rapid urbanisation generates risks and opportunities for sustainable development. Urban policy and decision makers are challenged by the complexity of cities as social–ecological–technical systems. Consequently there is an increasing need for collaborative knowledge development that supports a whole-of-system view, and transformational change at multiple scales. Such holistic urban approaches are rare in practice. A co-design process involving researchers, practitioners and other stakeholders, has progressed such an approach in the Australian context, aiming to also contribute to international knowledge development and sharing. This process has generated three outputs: (1) a shared framework to support more systematic knowledge development and use, (2) identification of barriers that create a gap between stated urban goals and actual practice, and (3) identification of strategic focal areas to address this gap. Developing integrated strategies at broader urban scales is seen as the most pressing need. The knowledge framework adopts a systems perspective that incorporates the many urban trade-offs and synergies revealed by a systems view. Broader implications are drawn for policy and decision makers, for researchers and for a shared forward agenda.

Exploring water conservation behaviour through participatory agent-based modelling

The growing importance of public participation and engagement within sustainability science has led to a reformulation of tools and methodologies that can be meaningful to both the researcher and the participants. One key strength of tools such as the agent-based modeling approach over more traditional equation-based approaches is that mathematical equations can be represented by soft sentences that make more sense to those not involved in model building on a daily basis. The problem of how to obtain relevant data and rules to incorporate into agent-based models, as well as seeking model validation by participants has clearly been recognized within the literature. Public participation and engagement is a vital ingredient in a three-stage process of field study, modeling, and simulation (or game playing). Such a methodology provides access to knowledge elicitation and social learning, developing a dual mechanism with implicit added value for both the participants and the modeler. This chapter explores the effects of social networks and imitation on water conservation, and lays some groundwork for further exploration of water conservation behavior using the participatory agent-based modeling approach. With further research into the role and importance of imitation in the uptake of water use beliefs, behaviors, and devices, it would be possible to use this approach to study and forecast the potential impact of campaigns targeted for specific water user profiles. Embedding such a study within the participatory agent-based methodology can start a dialogue with participants and stakeholders, engaging and increasing their awareness surrounding the issues of water use and water conservation as well as providing a valuable validation process for the modeler.

Participatory assessment of water developments in an atoll town

Water development projects often fail, which represents a poor outcome given the limited progress against the Millennium Development Goals in providing people with adequate water and sanitation services. This may not be surprising given that water management has been identified as being in the complex system domain. According to the Cynefin framework, many traditional approaches are not suitable; but it suggests an approach based on the methods of probe, sense and respond. In line with this general framework, a participatory assessment methodology has been used to explore experiences in the atoll town of Tarawa in the Republic of Kiribati. After framing the case study, information was collected providing multiple perspectives and these include narrative sources. When reviewing previous experiences, project implementations are seen as probes or disturbances to the system from which patterns of behaviour can be sensed. For this purpose, the critical factors leading to success or failure are described using network representations. These are then used to inductively sense system patterns, and the conclusions thereupon reinforce key recommendations in a recent United Nations report. Additionally, the findings in this paper feed into a larger study where Agent-based simulation and Bayesian networks are used in a participatory setting for integrated assessments.