Showing papers by "Joby Boxall published in 2013"

Development and Field Validation of a Burst Localization Methodology

Abstract: Reducing water loss through bursts is a major challenge throughout the developed and developing world. Currently burst lifetimes are often long because awareness and location of them is time- and labor-intensive. Advances that can reduce these periods will lead to improved leakage performance, customer service, and reduce resource wastage. In water-distribution systems the sensitivity of a pressure instrument to change, including burst events, is greatly influenced by its own location and that of the event within the network. A method is described here that utilizes hydraulic-model simulations to determine the sensitivity of potential pressure-instrument locations by sequentially applying leaks to all potential burst locations. The simulation results are used to populate a Jacobian matrix, quantifying the different sensitivities. This matrix may then be searched to identify different instrument locations to achieve required goals: maximising overall sensitivity to all potential events or selective sensitivity to events in different network areas. It is shown here that by searching this matrix to optimize such selective sensitivity, while minimising instrument numbers, it is possible to provide useful burst-localization information. Results are presented from field studies that demonstrate the practical application of the method, showing that current standard network models can provide sufficiently accurate quantification of differential sensitivities and that, once combined with event-detection techniques for data analysis, events can effectively be localized using a small number of instruments.

Aggregation and biofilm formation of bacteria isolated from domestic drinking water

Abstract: The objective of this study was to investigate the autoaggregation, coaggregation and biofilm formation of four bacteria namely Sphingobium, Xenophilus, Methylobacterium and Rhodococcus isolated from drinking water. Auto and coaggregation studies were performed by both qualitative (DAPI staining) and semi-quantitative (visual coaggregation) methods and biofilms produced by either pure or dual-cultures were quantified by crystal violet method. Results from the semi-quantitative visual aggregation method did not show any immediate auto or coaggregation, which was confirmed by the 40 ,6 diamidino-2-phenylindole (DAPI) staining method. However, after 2 hours, Methylobacterium showed the highest autoaggregation of all four isolates. The Methylobacterium combinations showed highest coaggregation between dual species at extended period of times (72 hours). Biofilm formation by pure cultures was negligible in comparison to the quantity of biofilm produced by dual-species biofilms. The overall results show that coaggregation of bacteria isolated from drinking water was mediated by species-specific and time-dependent interactions with a synergistic type of biofilm formation. The results of this study are therefore a useful step in assisting the development of potential control strategies by identifying specific bacteria that promote aggregation or biofilm formation in drinking water distribution systems.

Influence of Ground Conditions on Intrusion Flows through Apertures in Distribution Pipes

Abstract: This paper presents a new, tractable analytical expression to describe the intrusion of fluids into buried pipes under steady-state conditions. The expression is validated with results from novel experiments. The derivation is based on the combination of the relevant existing models of flows through porous media and the losses through an orifice, with the resulting expression relating the intrusion flow rate to an applied driving pressure. The expression is shown to yield results directly equivalent to those generated from a full three-dimensional (3D) computational fluid dynamics (CFD) model of the intrusion process. Results from the experiments, quantifying volumetric intrusion from a realistic 3D porous media, presented here, compare favorably with calculated values, validating the expression. Although the experimental and analytical results show a high level of agreement, it was found that the analytical expression tends to slightly underestimate the intrusion rate seen experimentally. The absolute difference in the values is low and is thought to be attributed to preferential flow path at the porous media and pipe interface that the analytical expression and CFD model do not include. It is shown mathematically and verified experimentally that the viscous and inertial resistance to flow in the porous media reduces the intrusion (or leakage) flow over that predicted by the standard orifice equation and places additional dependencies of the flow on the size of the intrusion orifice. The values obtained from the expression should be considered as a lower bound to intrusion (and leakage) rates, with upper bounds being provided by the standard orifice equation. Although developed to aid in the quantification of intrusion risk, such as that associated with water distribution systems, the expression is also validated for leakage for the limited case that the external porous media is considered to be fully compacted, consolidated, and immobile.

Linking distribution system water quality issues to possible causes via hydraulic pathways

Abstract: Our limited understanding and quantification of the variety and complexity of chemical, physical and biological reactions and interactions occurring within drinking water distribution systems currently prohibit the development of a deterministic model of water quality. The causes of known water quality anomalies can however be investigated through mining the large volumes of water quality, hydraulic and asset data currently being collected by utility companies. The data-driven methodology described here permits historical cause-effect linkages to be identified in a scalable, largely automatable fashion. Under Distribution System Integrated Modelling (DSIM), spatio-temporal searches within the set of pipes that typically lie upstream of a known water quality anomaly are used to identify possible causes. Understanding of the flow paths that connect causes and effects are derived from the results of hydraulic network simulations. DSIM was used to investigate contacts regarding discolouration and smell/taste issues from customers within a Water Supply Zone in England, UK, over a six-year period. 17.6% of discolouration issues and 17.4% of smell/taste issues were linked to maintenance jobs using the methodology, much smaller proportions than were identified using radial cause searches. The DSIM search results contained a greater proportion of one-to-one linkages and so are less ambiguous than the results of the radial spatio-temporal searches. DSIM was found to be a useful and informative tool for data mining multiple water quality related datasets.

Transforming Critical Infrastructure: Matching the Complexity of the Environment to Policy

Abstract: The application of complexity science to policy for critical infrastructure systems has never been more important. A number of issues highlight the need for policy to match the complexity of the co-evolving environment: increasing interdependency between utilities, uncontrolled demand leading to over use of diminishing resources, diverse technological opportunities with unclear investment choices, governance at different scales, public-private ownership differences and emerging business models. Systems are now so complex that people do not understand the interdependencies. Individual utilities are optimised with limited redundancy so that even minor failures can lead to major impacts throughout the whole infrastructure environment. This article proposes an ontology of critical infrastructure in which the points of conversion in the system are the generic units of analysis. Each conversion point has a set of properties representing its real world description. This ontological perspective highlights the inter-disciplinary nature of critical infrastructure systems. It also allows, through the adoption of an agent-based modelling approach, the simulation of different environmental constraints, such as those of resource availability. Methodologically, such modelling provides an abstracted view of infrastructure systems that simplifies the real world but allows policy options to be tested based on assumptions about behaviour in response to exogenous changes. Epistemologically, it focuses on a dynamic, co-evolutionary understanding of the system transition over time by examining holistic, systemic outcomes, connecting micro behaviours with macro structures. A case study of critical infrastructure in Yorkshire in the UK provides an exemplar of complexity in the real world. The model, a metaphysical representation, demonstrates how policy can be connected with the real world. This paper focuses on the infrastructure in the UK but the principles will apply to other countries.

A Multiaxial Notch Fatigue Methodology to Estimate In-Service Lifetime of Corroded Cast Iron Water Pipes

Abstract: The present paper summarises an attempt of using the so-called Modified Wohler Curve Method (MWCM) to estimate fatigue damage in pitted cast iron water pipes subjected to in-service variable amplitude multiaxial fatigue loading. In this setting, pits are treated as hemispherical/hyperbolic notches whose depth increases over time due to conventional corrosion processes taking places in buried cast-iron pipes. The validity of such an approach is proven by showing, through a case study, that, under particular circumstances, the combined effect of corrosion and fatigue can remarkably shorten the in-service lifetime of cast-iron pipes as observed in the case study.