Water Distribution Systems Analysis 2008

Cape Town depended for the first 250 years of its existence on water sources from Table Mountain. However, even prior to the South African War of 1899–1902, it was recognised that Table Mountain could no longer supply enough water, and that the mountains across the Cape Flats had to be tapped. The paper describes the moves, a century ago, by the then eleven municipalities in the Cape Peninsula, of which the Municipality of Cape Town was only one, towards unification. In 1913, all the municipalities (with the exception of Wynberg) of the then metropolitan area unified, and additional areas were also incorporated. (In due course the water supply position in Wynberg Municipality, sufficient in 1913, changed to one of impending shortage, and Wynberg joined this union.) Thus the unified City Council of Cape Town inherited the water problems of each municipality, and was forced to take action. Construction work on Steenbras Dam began in 1918; none too soon, because, before the dam was completed, water rationing had to be imposed. The need for adequate water was the single most compelling reason for the institutional reshaping of Cape Town's local government — this is the main finding of the paper.

The paper covers the history of Rand Water, the largest public water utility in South Africa, which was established over a hundred years ago following the discovery of gold on the Highveld of the Transvaal Republic, now Gauteng Province, South Africa. This history bears out the essential role that the engineering profession, specifically the civil engineering profession, plays in development. A challenge is issued to society to recognize this and allow the profession to play its role in the future for the benefit of society.

The 21^st century will witness widespread global changes due to climatic variation, demographic shifts, population growth and economic transitions. These changes are expected to have a significant impact on the quantity and quality of water resources and the timing of their availability across the globe. These impacts, in turn, will affect the performance and sustainability of the Nation's urban water resources infrastructure. In this context, the national water resources infrastructure includes engineered facilities for purifying and distributing drinking water, for collecting and treating wastewater, and for controlling and mitigating storm water. In anticipation of these far-reaching global changes, the U.S. Environmental Protection Agency is implementing a research program to identify and evaluate innovative approaches to improve the planning, design, operation and maintenance of the Nation's water infrastructure. A key question to be addressed by this program is, "How can the functionality of the Nation's aging water infrastructure be maintained and sustained to protect human health and preserve the environment for future generations in the face of profound global changes?" This paper focuses on the drinking water infrastructure. To help answer this question, the primary stressors and major trends expected to impact the functionality and sustainability of drinking water infrastructure are summarized here. Flexible mitigation and adaptation strategies to help drinking water utilities effectively cope with anticipated changes are outlined at a conceptual level.

In a developing nation such as South Africa, with its mix of first and third world service levels, effective master planning of water systems is vital. However, as backlogs are identified and services are provided, the master plans are in need of continuous updating. In this continuously evolving system the challenge is to develop and maintain accurate models of the existing systems as well as the relevance of the water master plans. Furthermore, it is also important to make the latest information easily accessible for the water system manager and his staff. The authors report on the integrated modelling procedure which has been developed in South Africa to update water master plans on a regular basis. The method, implemented widely in South Africa and also at some locations abroad incorporates an integrated approach to hydraulic network analysis and subsequent financial analysis, which includes demand modelling using actual metered data and calibration tests. Using case studies for illustration purposes, the paper reports on the dynamic master planning process. The discussion includes a description of the systems, methods and software which have been put in place to update water master plans on a regular basis. Aspects discussed include the organization and inclusion of as-built information as it becomes available for the pipe networks; the use of billing system information, linked to GIS coverage to populate the hydraulic models with up to date water consumption figures; modification of information regarding future development areas as services are implemented and new developments are planned; dealing with ad-hoc queries regarding system improvements when permission is requested to develop land and finally, providing a paperless GIS-based reporting system.

The strategic hydraulic model of the water supply and water distribution system of Belo Horizonte, 3rd largest city in Brazil, was developed based on the various data sources including ArcGIS, ESRI (Geographical Information System), CAD, elevation data, operation data, consumer information and billing information data, and telemetry SCADA (Supervisory Control and Data Acquisition) data. The strategic model consists of app. 13 200 pipes, 126 tanks, 145 pumps, and 387 control valves. Junction node demands were distributed based on the population polygons, measured flows at macro-measurement points, large water users; multiple demand categories were used including residential, commercial, industry, other, and leakage. Macro-calibration of the model was done based on the historical data and based on the selected data from the telemetry data. The macro-calibrated model was linked with OaSys, Telvent SCADA system in order to be prepared for automatic and periodic model update and for the forecasting simulations. Tailored demand forecasting module was developed for estimating water demands for the predictive extended period simulations based on the historical and current demand and meteorological data. The experience from developing off-line and on-line strategic model of Belo Horizonte including GIS and SCADA link is discussed in this paper.

Water Research Commission (WRC) of South Africa studies have found that franchising partnerships could alleviate and address many challenges in the operation and maintenance of water services infrastructure. Franchising brings appropriate training to those on-site, and also offers backup off-site skills together with the incentive to both call for those skills and to make them available. Findings indicate that many opportunities lie in the franchising of suitable elements in the water services value chain, and a selection of these has been modelled on paper. Procurement issues have been identified. Principles for embarking on water services franchising (for use by water services authorities, potential franchisors and potential franchisees) have been drafted.

Access to water is a key factor determining whether or not poor rural people are able to engage in economic activities. Many poor rural people in South Africa experience insecurity in terms of access to water. The reasons for this situation are manifold, but much can be traced back to inadequately informed planning; for too often services are not planned on the basis of an understanding of villager's real needs and capacities, nor based on the water resources potential to cater for these needs. When considering rural people's livelihoods strategies, it becomes evident that people require water for both domestic and productive needs. Research undertaken in relation to AWARD'S (Association for Water and Rural Development) work to improve the access of poor people to water resources in the Sand River Catchment in 2001; provided groundwork for our understanding of these needs. As a step further a methodology called SWELL (Securing Water to Enhance Local Livelihoods) that focused on enhancing participation of poor rural people in municipal water services planning was piloted in eleven villages of Bushbuckridge. This paper presents a methodology for assisting local government in water services planning to meet poor people's multiple water needs; based on the availability of water resources, the status of the infrastructure as well as demand and allocation of these resource.

As populations grow and current water supplies become more stressed, alternative new resources must be identified. In water scare areas, such as the semi-arid southwestern United States, communities have found it necessary to shift from reliance on traditional water supplies — ground water or relatively meager surface flows — toward a combination of large, engineered water projects, water reuse and conservation measures. Examples in the southwestern United States include Las Vegas, Phoenix and Tucson, each of which faces water-related engineering challenges. In the near future, these urban centers will be forced to rely on reclaimed water to satisfy their respective needs, as it is the only remaining unexploited water resource in this region. Current practice treats the water supply infrastructure design and operation as independent from the wastewater collection and treatment system. Often these systems are managed by separate departments or by different government entities. However, as water becomes scarcer, the interdependence between water distribution and collection systems must be recognized and exploited. Distributed, dual water treatment and distribution infrastructures and management plans are recommended as the most viable ways to accommodate future water demands. The present study addresses engineering and other significant challenges relevant to dual, distributed systems in water scarce regions.

In many water scarce communities across the world (e.g. Gold Coast - Australia, Hong Kong - China, Islands of the Caribbean and Pacific, and Windhoek - Namibia), non-potable water use/reuses have been employed. In essence, the non-potable water source (e.g. coastal/sea/ground saline water, mine effluent, sewage effluent, and grey water) is targeted at meeting non-potable water requirements (e.g. toilet flushing, landscape and/or crop irrigation, industrial (including mining) cooling and other processes) traditionally met using potable water. This therefore frees potable water to be used for previously unmet or increasing potable water requirements. For several reasons, the use/reuse of non-potable water for non-potable water requirements has been limited in South Africa. This is despite the fact that South Africa is a chronic water scarce country (500–1000 m³/person/annum) approaching absolute water scarcity (<500 m³/person/annum). Regulatory and guideline documents at the national, provincial and municipal level to implement such an alternative have been lacking. This paper highlights a few non-potable water reuse schemes that currently exist in South Africa and the strategic issues, which if adequately attended to, will facilitate a broader acceptance of non-potable water use/reuse.

South Africa is a semi-arid country with limited freshwater resources. Growing urbanization, industrialization and agriculture have placed significant demands on this resource with Water Service Authorities and Providers continually striving to efficiently allocate and optimally manage this resource for the various sectors. A proven measure to help meet increasing demand is the reclamation of wastewater for non potable purposes. Reclaimed water can be used for landscape and garden irrigation, some industrial processes (e.g. cooling, and air conditioning), toilet flushing, dust suppression, some construction water requirements, fire fighting, and environmental enhancement (e.g. maintaining urban stream flows and wetlands). Urban reuse of reclaimed wastewater is often conveyed through a dual distribution system, which comprises one system of pipes for conveying potable water and a second system of pipes for conveying reclaimed water. A variety of dual system configurations currently exist internationally. Effective planning of the reuse system, which considers potential water source(s), the water supply and distribution system, water demand, end user characteristics, water quality requirements and wastewater treatment, should occur in conjunction with the overall urban water system. These planning elements may be integrated and will result in multiple interactions and a variety of design configurations. This paper presents a model for assessing the potential for reclaimed wastewater reuse within a typical South African urban water system.

Water distribution systems produce greenhouse gases during the manufacture, transport and installation of pipes and also particularly as a result of pumping when electricity is derived from the burning of fossil fuels. Typically in a life cycle analysis for the planning of new water distribution system infrastructure, that involves pumping, a present value analysis is carried out to convert annual operating costs for pumping into their present values. The way in which time preferences are incorporated into the calculations strongly affects the outcomes in terms of both costs and associated greenhouse gases. Many water utilities around the world use a discount rate equal to the interest rate or the current cost of capital of between 6 and 8%. Over the last 5 years or so the United Kingdom has been using a discount rate for evaluating projects of 3.5% and declining to 1% between 30 and 301 years. The Stern Review: The Economics of Climate Change has recently recommended that a very low discount rate of 1.4% be used for evaluating projects that lead to the production of greenhouse gases. The Stern Review predicts that dire consequences will occur if the concentration of CO₂-equivelent greenhouse gases in the atmosphere exceeds 550 ppm and recommends that immediate drastic and decisive action be taken to progressively cut emissions by 3% per annum over the next century. This paper explores the different options for discount rates proposed for present value analysis by various economists and also considers the arguments for and against using the standard 6 to 8% or a significantly lower or a time declining discount rate that is based on societal preferences. The implications on the design of water distribution systems are assessed.

Generally improved access to computers and affordable software has promoted regular use of hydraulic modelling for design of water distribution networks worldwide. The bottom line to conduct such a design adequately has therefore been shifted to the quality of the model input data, which are often unreliable and/or incomplete for many networks in developing- and countries in transition. The paper demonstrates two possible approaches from the literature that can be used to assess the network reliability under the constraints caused by scarce information about the system, and in the absence of highly sophisticated network modelling software. These have been applied to the case networks from Indonesia and South Korea, respectively and the results were compared. In the first case, the EPANET hydraulic model has been developed together with a simple spreadsheet application to calculate the reliability and availability coefficients of the networks in two districts at the outskirts of the capital Jakarta. In the second study, the EPANET programme has been used to build a semi-pressure driven model of a secondary town, to test the sensitivity of the reliability- and availability factors for various ‘what-if' scenarios. The results show that despite some shortcomings, both methods offer a fair first indication about the network reliability and as such can be used in practice without of much additional coding or advanced modelling required. A few suggestions pointing further improvement have been listed in the conclusions.

Providing the rural poor with safe drinking water has been a national priority for the South African government since 1994, in line with the internationally embraced millennium development goals. After more than a decade of sustained and significant investment, it is time to address the sustained efficiency of the multitude of rural water supply systems that had been built. This paper reports on a proposed framework for allowing the rapid assessment of such a small rural water supply system.

Urban centralized water distribution systems in developing countries are facing various problems. For the population depending on the distribution systems, the impacts can be summarized to the inadequate amount and quality of disseminated water. Numerous technical and socio-economical deficiencies lead to an insufficient water supply. Amongst others, significant and strongly connected deficiencies are the lack of a central data management, the very complex network topology and the intermittent operation and supply. This article outlines the deficiencies and presents a strategy to improve existing deficient water distribution systems with such characteristics. The final objective of the strategy is the introduction of a continuous supply as a technical constraint for a sustainable water distribution and save supply. Apart from technical needs, a continuous supply is desirable in terms of equity in supply to customers and quality of life of customers. Further, an overview of a specially developed adapted integrated planning and analysis tool is given. The application of the strategy and the tool is shown in the context of the project IWRM for oases in Béni Abbès, Algeria.

The effects of climate change on municipal water distribution systems are not well known. The Intergovernmental Panel on Climate Change (IPCC) has forecast higher mean temperatures for the mid-latitude region of North America. The aim of the paper is to begin to understand the impact of higher temperatures on nodal demands and the mean and coefficient of variation of nodal pressures in water distribution networks. The second order second moment (SOSM) method was used to assess the impact of higher mean temperatures on the mean and coefficient of variation of nodal pressures in the Anytown network. Under maximum hour demand (MHD) and maximum day demand (MDD) with fire conditions, the warming scenarios were shown to have a detrimental effect on the ability of the Anytown network to meet minimum pressure specifications. Node location within the Anytown network influenced the impact of higher temperatures on the mean and coefficient of variation of pressure. Strategies to ensure an acceptable hydraulic performance under future warming scenarios were discussed.

Average demands are estimated based on population densities, typical usage by consumers, customer billing records, and other factors but are not appropriate for real-time modeling. Good nodal demand estimates to analyze and respond to pressure and water quality events are critical, however, approaches to estimate them are lacking. This paper presents a real-time demand estimation method using a recursive state estimator that is based on a weighted least squares (WLS) scheme. It is shown that pipe flow field measurements contain the most information for estimating nodal demands. Since the number of measurements will typically be less than the number of nodes in the system, regions with similar user characteristics are grouped and assumed to have same demand patterns. The demand estimation uncertainties propagated from field measurement errors and model simplification errors are quantified in terms of confidence limits using first order second moment (FOSM) method and the results are verified by Monte Carlo simulation. Application to a simple network with synthetically generated demands shows promising results.

There is growing interest in modeling water demands on short time scales (as brief as one second) and small spatial scales (typically single homes). Buchberger et al. (1996, 2003) have developed the Poisson Rectangular Pulse (PRP) model for this purpose. Blokker et al. (in prep.) have developed an end-use model SIMDEUM (which stands for SIMulation of Demand, and End-Use Model) which is based on statistical information from end-uses and does not require any flow measurements. SIMDEUM was developed and validated for Dutch water use. In this paper the PRP model and SIMDEUM are compared with each other and with measured indoor water demands from 21 homes in Milford, Ohio. Both models compare well to the measurements; the PRP model works better in simulating the cumulative flows of a sum of 20, SIMDEUM works better in simulating the flows of a single home.

Demands for water in a municipal pipe network can exhibit strong spatial correlation owing to similar daily schedules among residential users and other consumers. This paper shows how to specify a diurnal demand pattern to preserve a desired degree of cross correlation among network water users. The influence of temporal averaging and spatial aggregation on the level of cross correlation among nodal water demands is clarified. The effect of spatially correlated network demands on the magnitude of the pressure head and on the migration of a contaminant intrusion is examined. For the range of conditions explored here, results show the correlation between water demands does not have a significant effect on the average nodal pressure head in a system with conventionally sized pipes. However, highly correlated water demands lead to larger variations of nodal pressure head, which result in larger probabilities of pressure failure. In addition, the average pressure head at any time ultimately depends on the parent pattern provided.

The District of West Vancouver, British Columbia, Canada started investigating a universal metering program with the endorsement of its Water Conservation Strategy in 2002. Extensive investigation was done regarding the benefits of metering and it was agreed that metering would provide valuable information about how much water is used, by whom, where and when. It was anticipated that this information could be used for both water system management, demand side management and the billing of customers which, in turn, would support the District's water conservation initiative. A universal metering program was started in 2005. More than 12,100 meters are already installed and the water consumptions of about 18,600 customers have been read on a monthly basis since January 2007. The District opted to install a radio based metering system that made it possible to read meters remotely via radio frequency. This paper reviews the procedure the District went through during the implementation of its universal metering program and focuses on: 1). the use of water consumption data to support utility billing, 2). the verification of meter readings, 3). water tariff and revenue analysis, 4). unaccounted-for-water calculation and 5). hydraulic modelling. The authors of this paper were closely involved in the data integration and software development to support the District of West Vancouver in this process and are currently responsible for the monthly processing, reporting and analysis of all meter readings on behalf of the District. A web based application was developed where monthly consumption data and reports are published and made available to key staff members and management.

The Department of Public Works (Head Office, Pretoria) awarded a performance contract tender for energy and water savings to SEM in Dec. 1999. We started working on the contract in Jan. 2000. The sites are in the Johannesburg region, south of Midrand. Within the first year the potential of water savings already became clear. The monetary value of the water savings turned out to be 80% of the savings. The average water savings on 24 sites is close to 50%, compared to the energy savings that is 20%. Some sites run at 10% of its original water consumption. The total water saving per month on the 24 sites is about 350 000 m³ of water, which represents about 0.35% of water supplied by Rand Water. The paper will point out the basic strategy that was followed on the relevant sites to achieve these savings. Some statistics will be given and graphs of water consumption to indicate the reduction in consumption. The 24 sites are divided in four categories, which are offices, military bases, prisons and police stations. The importance of continuous monitoring and continuous maintenance to maintain the low level of consumption, is high lighted. The paper proves that the potential for water savings in general is between 10 and 90%.

South Africa is a semi arid country and several of our urban regions (e.g. Cape Town and Polokwane) have had to implement emergency water restrictions in recent years. The costs of augmenting urban water supplies are very high, but future augmentation schemes can be delayed if consumers become more efficiency minded in their use of water. A water efficient device (e.g. a modern 4.5 litre cistern and pan combination) is one which performs exactly the same function as an outdated device (e.g. the old 13 litre cistern and pan), but uses less water. Awareness of water efficiency in South Africa among the public, in the building profession and at municipal level is still relatively low. A move to water efficiency is evident on the showroom floors of the plumbing marker suppliers, but this is driven by international trends rather than local factors. Commercial institutional investors in South Africa are also showing signs of moving to water efficiency. In order for water efficiency to become the norm in South Africa amendments must be made to the national building code. Amendments to municipal bylaws can also be helpful, but the building industry works primarily with the building code and cannot be expected to keep track of the variations within the bylaws of South Africa's 169 Water Supply Authorities. The state is a major employer and building owner in its own right and needs to lead by example by moving to water efficiency in its own buildings.

Water Distribution Network design has been traditionally approached as a cost minimization problem, constrained by some additional restrictions intended to ensure an acceptable level of customer service. Although the ideas have existed for same time, it was only recently that various researchers developed new network optimization approaches trying to address the minimization of design costs, while maximizing the benefits through some other performance indicators assessment in a risk-based scenario. Unfortunately, network simulation is still performed within a demand-driven context, even when reliability is considered among the benefits, and leakages are given as a constant percentage of nodal demands instead of being computed as a function of pipe pressure. This article introduces a more realistic approach to network design and simulation, performed using pressure-driven leakages employing a recently developed simulation model. Thus, the design procedure is conceived as multi-objective optimization, performed considering the minimization of pipe cost and together with total network leakage flow. The approach was tested on a small-size Italian real network which supplies an industrial area, and on a simpler network that yielded some interesting observations about the proposed paradigm.

An index-based method for the evaluation of the environmental impact of water distribution systems (WDSs) is introduced. A number of environmental measures are incorporated into the index-based method to account for local, regional and global non-renewable resource consumption, greenhouse gas emissions, and emissions to air, land, and water. The index-based method is applied to designs provided in the literature for the Anytown system. Design alternatives are compared on the basis of environmental impact index and cost. For the system analyzed, results show that the four most environmentally feasible alternatives are also the four most cost-effective alternatives. System analysis also shows that substantial increases in total system cost results in an increase in the environmental impact index amongst alternatives, while the relationship between the environmental impact indexes is not well defined amongst alternatives with similar costs.

Recent research has emphasised the need to consider sustainability as a key objective of water supply systems. In a previous publication, the principal author presented a methodology for considering the total energy of a water distribution system (WDS) as an effective measure of the sustainability of the system. The total energy (including embodied energy of the materials as well as the energy consumed in the operation of the system) is closely related to the greenhouse gas emissions associated with the system. Most optimization studies of WDS have optimized a single objective such as capital cost or the net present value (NPV) of capital plus operating cost. A few multi-objective studies have been carried out previously but few have effectively considered sustainability objectives. In this study, a multi-objective genetic algorithm was used to identify the Pareto optimal trade-off between cost and total energy for a simple WDS. This technique does not identify a single "optimum" design but rather a set of technically efficient solutions each of which places a different relative weight on the two objectives of cost and total energy. The results for the test WDS demonstrate that different designs are obtained when minimizing the total energy of the system compared to minimizing cost alone. There are also compromise solutions between these two extremes. The methodology presented represents an advance in the consideration of sustainability in the design of WDS.

Climate change, especially global warming caused by human activities presents serious global risks. Mitigating global warming by reducing greenhouse gas (GHG) emissions is a unique challenge facing our generation. In order to tackle this challenge, many measures are being developed, among which carbon trading is a popular one. In this paper, a new paradigm for the design of water distribution systems (WDSs) is being developed under a possible emission trading scheme. In this paradigm, minimisation of the costs of GHG emissions is incorporated into the optimisation of WDSs either as one part of the objective or as a second objective. A multi-objective genetic algorithm (MOGA) called WSMGA (water system multi-objective genetic algorithm) has been developed to solve this problem. The time value of both the system costs and the costs from GHG emissions has been taken into account by using present value analysis. Following the Stern Review Report there is controversy as to what discount rate should be used in present value analysis for mitigation of climate change, consequently two different discount rates have been used in this study. The impacts that the carbon prices used in the emission trading scheme have on the optimisation of WDSs have been explored for two hypothetical case studies. The optimisation results show that the different carbon prices used lead to different solutions in the single-objective optimisation formulation. In general, a network with larger pipes is chosen when a higher carbon price is used. In contrast, the carbon price used has no impact on the multi-objective optimisation results. However, different carbon prices lead to different amounts of savings in greenhouse gas costs resulting from the same amount of increase in system costs for the same ordered set of Pareto-optimal solutions.

Energy expenditure from pumps in water supply systems can account for up to 50 % of the running costs of a water distribution system. The purpose of this paper, based on the second author's MSc dissertation is to present the results of cost-benefit analyses with regards to pumping costs for a water distribution system if it were to be designed form scratch. A case study of a real life system is used to demonstrate the methodology proposed. Current practice involves pumping to high water tower elevations and in many cases reducing system pressure in areas of the network by use of pressure reducing valves (PRVs). This causes unnecessarily high pumping costs and may also lead to leakage and bursts within the system. The proposed alternative considers pumping to lower elevations with subsequent boosting to regions with low pressures in order to reduce the risks of leakage and pipe failure, as well as pumping costs within the system. It was found that the use of boosting pump in a system with low tower elevation proved to be up to 19% more cost-effective than using PRVs in systems with high water tower elevations.

Water Distribution Network enlargements are caused by growth of demands inside the network and by geographical growth of the network itself. For a water supply system operator, it is very important to have optimum designs of such enlargements and carry these works out at a minimum cost and in a way that makes it possible to satisfy the new demands without deteriorating the service in terms of continuity and minimum required pressure. This paper presents a new methodology for the optimized design of Water Distribution Network enlargements; it is based on the application of two concepts that are related to the degree of vulnerability of the network: resilience and unitary power. This methodology allows to find optimum supply routes and appropriate diameters in order to convey the needed flow from the supply sources to the enlargement areas. Furthermore, the obtained designs were analyzed in terms of costs and were found to be close to the economic optimum designs achieved by means of artificial intelligence techniques.

Pipelines are prone to leaks, bursts, damage and poor jointing. The longer the pipeline, the greater the risk of downtime to make repairs. The engineer frequently does not relate the standards to the risk. The greater the geometry of the pipeline the bigger the risk. A systems analysis is required to select the correct reliability factors. Pipelines are subject to failures on a scale proportional to length and diameter. Materials, laying and supply also are subject to quality variation. The cost of failures increases with risk. In an attempt to minimize risk of down-times, intermediate storage and isolating valves are required. A 400km long Glass fiber reinforced pipeline in Botswana is used as a case study. It is found in the risk study that length, diameter and laying conditions are in that order the main effects on risk. The optimization spreadsheet was designed showing the relations between the isolation valves intervals and the costs involved. The optimum cost of valves installation was computed by augmenting the cost of completed valve chambers and the cost of water lost over a certain distance. These computations were carried out for each of the four pipe diameters along the line. The least combined cost of valve chamber per kilometer and water lost cost per kilometer were used to define the optimum number of valves required over each section of the specified pipe diameter. This study also addresses the optimization of reliable emergency storage reservoirs near water treatment works. Currently, there are three major centers that are supplied by the North South Carrier pipeline, namely Palapye, Mahalapye and Gaborone. During pipeline failures these centers face shortage of water, when there is no pumping at all because all pump stations are synchronized with the three water works. Pumps run only when there is demand from the treatment plant. When the transportation system shuts down, the treatment successively comes to a halt, cutting supply to the consumers. This is the scenario, which is experienced during the down time — when the system fails. Lack of emergency supply in the system is the main source of this problem. Cost effective and efficient planning, design and construction of system elements like valves and reservoirs can be optimized to curb the down time impacts on the water authorities and the consumers.

Drinking water distribution networks are important because they provide water to meet basic human needs, and to protect humans in the event of fires and other public emergencies. With aging infrastructure, there is an urgent need to design water distribution networks to ensure safety and reliability of service in the future. The uncertainty that surrounds future scenarios of climate-induced drought, population levels, and urbanization patterns — all factors that influence water demand — means that a system design chosen today may be inadequate to meet future demands in a water distribution network. Water utilities often have to plan the design of their water distribution network with only limited information on future water demand levels. For example, if water demand in the future is higher than the level predicted at the time of design, then a municipality will eventually have to retrofit the system, perhaps at great expense, to meet the unanticipated water demand. Thus, there is a need for methods to design networks to minimize the need for future system retrofit under uncertain demands, and to make networks economically robust. In this paper a new framework is presented to design water distribution networks for economic robustness. Economic robustness supplements the least-cost optimality criterion by providing a measure of the variability involved in retrofit costs of a system under uncertain future conditions. In the new framework, water demand projected at the end of a 20-year planning period is treated as an uncertain quantity and modeled as a random variable with an error probability density function (PDF). In the proposed framework, new criteria such as the expected value and standard deviation of retrofit cost are developed to evaluate the economic robustness of water distribution networks. The framework is applied to a simple network, with comparison of design alternatives done on the basis of pipe cost and expected retrofit cost. The results obtained indicate that surplus hydraulic capacity lowers the uncertainty of future retrofit costs and increases confidence of retrofit cost estimates. Consequently, the results substantiate the intuitive understanding of the benefits of surplus hydraulic capacity in a system.

Historically, the minimum diameter of a pipe in a municipal water distribution system has been governed by fire flow requirements. In most cases across North America, the minimum allowable pipe size is six inches (150 mm), even on branching stubs that feed 100 or fewer homes. These peripheral regions of the pipe network often experience low velocities, long residence times, poor water quality and accumulation of settled deposits. As a consequence, many water utilities routinely flush these lines in an effort to cleanse them. In recent years, several water utilities (most notably in the Netherlands) have introduced the concept of a "self-cleaning" network where, for several minutes each day, a critical pipe velocity occurs and resuspends particles that settled during the low flow periods. Self-cleaning networks are a radical departure from the typical looped distribution system. Self-cleaning networks have a branch-type arrangement with downstream declining diameters and unidirectional velocities that reach at least 0.4 m/s for several minutes each day. Peak flows in the self-cleaning network are estimated using an empirical "q square root N" method, where q is the tapping unit demand usually taken as 0.083 litre per second per unit and N is the number of tapping units in the neighborhood. The problem of estimating the peak flow and, hence, the required pipe diameter can also be investigated using basic principles from the Poisson Rectangular Pulse (PRP) model for residential water demands. The objective of this paper is to apply theoretical results from the PRP model to generate reliability based estimates of the peak flow and the corresponding pipe size needed to assure a critical self-cleaning velocity as a function of neighborhood size. Results from the PRP model are compared against the conventional but conservative"q square root N" method.

This paper presents a novel methodology for assessing an isolation valve system and the portions of a water distribution network (segments) directly isolated by valve closure. Planned (e.g. regular maintenance) and unplanned interruptions (e.g. pipe burst) occur regularly in water distribution networks making it necessary to isolate pipes. To isolate a pipe in the network, it is necessary to close a subset of valves which directly isolate a small portion of the network, i.e., causing minimum possible disruption. This is not always straightforward to achieve as the valve system is not normally conceived for isolating each pipe separately (i.e. locating two valves at the end of each pipe). Therefore, for management purposes, it is important to identify the association between each subset of valves and the segments directly isolated by closing them. This is also important to improve the design of the isolation valve system in order to increase network reliability. Thus, this paper describes an algorithm for identifying the association between valves and isolated segments. The approach is based on the use of topological matrices of a network whose topology is modified in order to account for the existence of the valve system. The algorithm is tested on an Apulian network where the isolation valve system is designed using a classical multi-objective genetic algorithm as an optimizer.

Water distribution system (WDS) design has been the subject of minimal improvements over the last decade, despite the fact that the accessibility of computer models has increased. Water distribution pipes are designed to provide adequate pressure at distribution nodes and reasonable velocities in pipes. This is usually done with a hydraulic solver coupled with the engineering expertise of the designer. Storage tanks are designed according to standard requirements considering minimal values provided by local guidelines. Storage tank allocation is generally done without taking into account the network capacity and robustness. Tanks are located next to the distribution area with highest demand and considering other site-specific constraints (topology, multiple pressure-zone systems, etc.). Optimal network configuration, in terms of hydraulic efficiency and water quality, is rarely considered. Long residence time results in the loss of disinfectant residual and favors water quality degradation. Up to now, the optimization of the WDS design and operations have mostly focused on pipe sizing and pumping schedules without taking into account storage tank locations, storage capacity and water quality. The purpose of this paper is to present a new methodology to optimize water storage tank volume and location. This methodology, will take into account hydraulic requirements as well as water quality requirements (by minimizing the residence time in order to reduce disinfectant decay and disinfection by-product formation). The proposed methodology will be tested on a small study case. The optimization model, linked with EPANET, is applied to this benchmark and results are analyzed.

This paper aims at presenting the historical evolution and the present status of water distribution network design approaches in the light of water losses reduction. Although pressure management has been recognised as one of the four actions aimed at reducing water losses, very little work is currently available in the literature on design criteria that would allow improving pressure management in operation. Only recent works have aimed at improving design of new systems or expansions and rehabilitation of the existing networks by formulating a multi objective problem, where the first objective is clearly the reduction of costs (network, non revenue water, maintenance), while additional objectives, aim at improving resilience of the system by reducing the internally dissipated power and at redistributing more evenly the pressure field over the entire water distribution network. The new techniques have the advantage of producing networks that can be operated under lower pressure fields, which is the objective of pressure management. The new multi objective optimization techniques are generally based on genetic algorithms, which make extensive use of network analysis and simulation. Therefore the paper also discusses the representation of leakage losses in the current generation of water distribution networks simulation packages. The presently available approaches are shown to be unsatisfactory in that they produce considerable errors in terms of energy and head losses. The paper concludes by presenting a set of possible alternatives and future perspectives.

An efficient water network design is a balance between network cost, reliability, performance and appropriateness to the community. The application of the analytic hierarchy process and an array of reliability measures to the design of a water distribution network in a peri-urban area is described. Fieldwork was carried out to ascertain the relevant topographical, demographic and socio-economic data for the study area. In addition to the capital cost and performance indicators for the water distribution system, social and health-related issues were included in the design process. The results showed that a design with a high value of statistical entropy, reliability and redundancy would also have a higher cost. When the analytical hierarchy process was used to carry out a systematic assessment of the various trade-offs, the more expensive but reliable networks were determined to be more appropriate.

A new optimization model for determining the minimum cost for the design of water distribution systems is described in the paper based on a combination of linear programming methodology (LP) and a genetic algorithms approach (GA). A many different heuristic algorithms have been developed in the last two decades and applied to the design of water distribution systems. Although many research efforts have been made for the sake of achieving the optimal design of the looped water distribution networks, there is still some uncertainty about finding a generally reliable method. The author of the paper is proposing a method in which the main emphasis is placed on its higher reliability of finding an optimal solution in terms of closeness to a global minimum. In this study the efficiency of GA optimization was improved through a hybrid method, which combines the GA method with a linear programming methodology. The GA method is used in the outer loop of the proposed algorithm, which is intended for decomposing a complex looped network to a group of possible branched networks. The mathematical models using LP are then set up in an inner loop for each member of this group of branched networks for their optimization. After evaluating the high number of possible branch networks (by LP which is nested in a GA fitness function), an optimal solution could be found for the original looped network.

The multi-objective design and rehabilitation of water distribution systems (WDS) is defined as the search for the set of system designs which offer the best trade-off between a set of competing design objectives. Typically these objectives will consist of the cost of implementing a system design and a measure of the performance of that design. A recent development in the field of evolutionary algorithms is to use probabilistic methods to identify key building blocks (short, highly fit groups of genes). Probabilistic Model Building Genetic Algorithms replace the traditional crossover and mutation methods for the generation of offspring with the building and sampling of a probabilistic model describing the genomes in a set of promising solutions. Other methodologies use similar probabilistic methods to identify building blocks, but continue to use the traditional techniques of crossover and mutation with the condition that building blocks cannot be split. This paper compares the performance of three evolutionary algorithms which employ probabilistic building block identification to speed up convergence with that of the well known multi-objective genetic algorithm NSGAII for the multi-objective optimisation of a real world WDS. In particular the Univariate Marginal Distribution Algorithm, the hierarchical Bayesian Optimisation Algorithm and the Chi-square matrix method for building block identification are considered.

Practical hydraulic design is focused only on designing a network that will provide pressure at or above a minimum required to fight a fire in the system without any explicit consideration of potential economic damages to buildings and their contents consumed by fire. The inclusion of economic damages in the design optimization of water networks could help utilities allocate capital resources (pipes, pumps, tanks) to protect valuable infrastructure and people in key areas of a network during a fire. This paper presents a new water distribution network optimization framework that includes in its objective function the cost of pipes and the potential economic damages sustained in fires. The new optimization framework incorporates the uncertainty of design fire flows by modeling them as random variables. A new measure of expected conditional damages is developed and used to quantify potential economic damages sustained in a fire, given the uncertainty associated with design flows. The expected conditional damages function is solved with an efficient numerical integration technique. A case study is applied to the new optimization framework with a Particle Swarm Optimization (PSO) program.

The design of a water distribution system (WDS) is a challenging problem involving multiple conflicting objectives. The goal of multi-objective WDS design optimization is to find the set of solutions which embodies the Pareto-optimal trade-off between system cost and benefit (typically some measure of reliability). This provides decision-makers with a broad understanding of design possibilities, allowing them to identify a solution with the maximum cost-benefit, or maximize benefit subject to a given budget. A WDS must be designed in order to satisfy consumer demand at required pressures, handle multiple demand loading conditions, withstand component failure and degradation, and provide surplus capacity for growth. In this paper, a jumping-gene (JG) evolutionary algorithm is applied to multi-objective WDS design, and tested on a number of established WDS benchmarks. The JG algorithm is compared to the Non-dominating Sorting Genetic Algorithm II (NSGA-II). Results indicate that the JG algorithm is comparable to the NSGA-II, yet sufficiently different to warrant consideration, particularly in terms of finding high reliability looped configurations. It is argued that the JG mechanism is capable of mimicking how an engineer might exchange capacity between various parts of a system in the course of the design process, and as such is able to find robust alternative designs which may elude competing algorithms.

Design optimization of looped water distribution networks has been a thoroughly researched problem for the last four decades. However, very few works have been published dealing with the optimal design of complex water distribution networks containing various network elements, such as the "Anytown" water distribution network. The central theme of the present work is to develop a design model satisfying the following requirements: (i) GAs are developed for unconstrained optimization problems. That is, they have difficulty in handling constraints in a constrained optimization problem, so the solution strategy should reduce the number of constraints that must be handled by GA and (ii) existing/new tanks should utilize their full operational capacity and exhibit good recirculation capabilities such that water quality problems are reduced. Keeping these two aspects in mind a new optimization model including a tank design procedure, which requires complete description of a tank's parameters, is proposed. Minimization of Network cost and maximization of flow entropy are considered as the two objectives. A multi-objective genetic algorithm, namely NSGA-II, is used and the efficacy of the proposed model is demonstrated. It will be shown that the flow entropy could be used as a surrogate reliability measure and that it alleviates drawbacks of some of the other surrogate measures such as resilience index. New results obtained for the "Anytown" network show that the model manages to find better solutions and satisfy all the constraints including pressure constraints in EPS.

The optimisation of pump operations in water distribution networks is an ongoing research topic motivated by the great energy savings that a careful scheduling of pumps may achieve. State-of-the-art approaches often combine an optimisation algorithm, such as Evolutionary Algorithms, and full hydraulic simulation. Despite the advances in optimisation techniques and hardware performance, the time required to obtain a near-optimal schedule is still measured in hours. Multiple CPUs are increasingly used to parallelise tasks that require a high computation time. In fact, parallel optimisation algorithms are widely present in the literature. On the other hand, hydraulic simulators that support parallel computation are scarce. The most popular research simulator, EPANET, was not designed with concurrency in mind. In this paper, a new thread-safe variant of the EPANET Toolkit is proposed. As an application example, we propose a parallel variant of an Ant Colony Optimisation (ACO) algorithm for optimal pump scheduling in water distribution networks. The thread-safe EPANET library is combined with the parallel ACO algorithm to achieve reduced computation time in a multi-core computer. Experimental results show that an initial computation time close to 2 hours may be reduced to less than half an hour without sacrificing the quality of the results. The number of ants is also identified as a parameter that influences execution time in the parallel ACO approach proposed in this paper.

This paper presents an application of a rapid prototyping tool utilising Single-Objective and Multiple-Objective Genetic Algorithms (GA) to optimization problems defined using spreadsheets. The tool is implemented as an add-in for Microsoft Excel® which combines a robust and powerful C++ library of GAs with a familiar user interface allowing for a fast and easy definition of objective functions. The tool can also be easily linked with various hydraulic solvers (e.g. EPANET) using VBA and thus presents a great instrument for researchers and practitioners who want to solve complex optimization problems (e.g. design, rehabilitation and calibration of water distribution systems) with a minimum of additional programming. The capabilities of the tool are demonstrated on the Hanoi Water Distribution System design problem as a multiple-objective optimization and the performance in terms of quality of obtained solutions is compared with those obtained with a single-objective formulation.

The application of the reliability analysis techniques to the water distribution systems aims to properly achieve in probabilistic terms the fulfilment of the nodal demand in a conceptual and physical context subject to different causes of uncertainties. The availability of system components, like pumps or pipes subjected to failure, the uncertainty in the spatial - temporal behaviour of nodal demand, the pipe roughness, the reservoir level as well as the availability of supply resources contribute to the definition of the system reliability. Nevertheless the complexity of a reliability model increases with the number of different uncertainties, and usually, for each specific case, only few parameters are assumed as random while the remaining are fixed as deterministic. This fact always implies more or less limitations in the system description also when deterministic assumptions are based on reasonable hypotheses. To overcome this shortcoming, a mixed analytical - numerical approach, able to take into account both the mechanical failure of system components and the random spatial - temporal distribution of nodal demands, is here developed. The goal is achieved by joining a Monte Carlo numerical approach based on the head-driven simulation with a First Order Second Moment (FOSM) closed form solution (Xu and Goulter, 1998). The Monte Carlo approach lets to analyze the series of partial shutdowns related to the renewal process of pipes and the time evolution of the demand, while the spatial variability of the latter and the uncertainty in the pipe roughness are described by the FOSM approach. An illustrative example developed in the well-known case of the Anytown network, demonstrates that the uncertainty related to the spatial nodal demand and pipe roughness may have a relevant impact on the reliability evaluation of a distribution network whose pipes are subject to the mechanical failure.

In order to successfully manage critical infrastructure systems in particular those of water supply networks, there is a need to identify, assess and control various factors that may contribute to harming the supervised area. These factors have dependencies in a large set of heterogeneous information, which is often owned by different entities and data sources. All this information needs to be integrated to allow seamless use and consistent management, and after consolidation it can be reliably and quickly, communicated. This paper deals with the design of a Knowledge Based Expert System (KBES) able to provide an ‘on-line failures recognition and assessment' of tightly interconnected, technological infrastructures. This in turn contributes to a machine- readable, integrated, conceptual model of the whole system. In particular the aim of this paper is to present an intelligent software tool, using Artificial Intelligence (AI) techniques which allows the execution of an alarm analysis, through the remote sensing activity of complex plants. The AI component is based on CLIPS (C-Language Integrated Production System) which is a tool that offers a complete environment for developing a rule-based expert system. The AI component allows identification of the primary faults of the system, discriminating these former from other offshoot alarms. In other words, this tool shows which alarms are directly connected to primary faults and which alarms are consequential effects of the primary ones. The core of the software is an algorithm which uses a knowledge ontology and a set of alarm propagation rules which are both based on the Multilevel Flow Modelling (MFM) paradigm. The proposed algorithm has been tested integrating it with EPANET and by simulating some fault scenarios and analyzing the results.

This paper describes a conceptual risk-based decision support methodology for the operation of water distribution systems (WDS). More specifically, the methodology focuses on providing near real-time support to network operators to improve their response to failure conditions, such as pipe bursts, equipment failures, etc. The risk related to the impact of failures in WDS is used to guide, in near real-time, the operator's approach and response to the failures. The impact metric of each failure is formed by a value tree comprising several basic impact factors affecting either the water utility or the customers. The impact assessment is undertaken by using a pressure-driven hydraulic model coupled with a Geographic Information System (GIS) considering explicitly the vulnerability of individual types of customers within the areas (potentially) affected by the failures under investigation. An intervention manager is also developed to assist the operator in testing the appropriateness of proposed interventions/responses to each failure. The intervention manager provides suggestions for improved courses of action determined through offline analyses of the system, stored in an interventions knowledge base in the form of ordered sets. The reduction of risk for each intervention is evaluated and compared to a "do nothing" alternative explicitly supporting risk-aware, near real-time decision making.

Pressure management in water distribution systems (WDS) is an important issue for water companies as it can lead to substantial savings. This paper presents a mathematical model for evaluating the associated benefits and costs assuming the use of Pressure Reducing Valves (PRVs). The model is developed as a stand-alone methodology which subsequently could be used to provide the objective function for an optimisation algorithm that will be developed to automate the process of selecting, locating and setting up PRVs. The methodology addresses benefits and costs arsing from reduced water leakage, reduced pipe burst frequency, reduced pressure-sensitive demand, reduced energy consumed, reduced active leakage control effort, reduced frequency of customer contacts and installation/operation of PRVs. The methodology developed is tested on two real-life District Metering Areas (DMAs) in the UK where pressures are reduced by installing different types of PRVs at each DMA's entry point. The results obtained demonstrate the importance of quantifying other benefits and costs in addition to those conventionally analysed, e.g., leakage reduction benefit and the cost of PRVs.

The electric energy market liberalization recently occurred in many countries of the world has allowed the diffusion of electric rates that promote off-peak period energy usage in the night hours and penalize peak period energy usage in the diurnal hours. In this paper, a methodology for strategic planning and management of simple pumping stations in small Water Distribution Systems (WDS) for which "ad hoc" electric pumping cost estimations are not usually carried out, is proposed. In particular, an ‘a priori' evaluation of the best operating planning to be adopted in order to minimize pumping during peak periods and maximize it during off peak periods while also satisfying the system constraints and users' demands, is implemented by means of the identification of a few synthetic indices such as the capacity of the tank, the pumped water volume, the mean water demand, etc. The proposed methodology is based on the simulation of a large number of theoretical water distribution system configurations and tested in a number of Italian real-life water distribution systems. The preliminary results show the proposed indices as useful tools to be adopted for an ‘a priori' evaluation of the best operating pumping strategy in terms of both energy and costs saving.

Water service providers (WSPs) in the UK have statutory obligations to supply drinking water to all customers that complies with increasingly stringent water quality regulations and minimum flow and pressure criteria. At the same time, the industry is required by regulators and investors to demonstrate increasing operational efficiency and to meet a wide range of performance criteria that are expected to improve year-on-year. Most WSPs have an ideal for improving the operation of their water supply systems based on increased knowledge and understanding of their assets and a shift to proactive management followed by steadily increasing degrees of system monitoring, automation and optimisation. The fundamental mission is, however, to ensure security of supply, with no interruptions and water quality of the highest standard at the tap. Unfortunately, advanced technologies required to fully understand, manage and automate water supply system operation either do not yet exist, are only partially evolved, or have not yet been reliably proven for live water distribution systems. It is this deficiency that the project NEPTUNE seeks to address by carrying out research into 3 main areas; these are: data and knowledge management; pressure management (including energy management); and the associated complex decision support systems on which to base interventions. The 3-year project started in April of 2007 and has already resulted in a number of research findings under the three main research priority areas (RPA). The paper summarises in greater detail the overall project objectives, the RPA activities and the areas of research innovation that are being undertaken in this major, UK collaborative study.

Discolouration incidents in the drinking water distribution networks are caused by the resuspension of loose particles. Removing particles will consequently reduce the discolouration risk. Unidirectional water flushing can be an effective method when strict boundary conditions are met like a minimum velocity of 1.5 m/s, flushed volume 2 to 3 times the content of the pipe and using a clear water front. Supposedly adverse effects of cleaning of cast iron pipes are that the protective layer of corrosion products can be damaged leading to increased particle production post cleaning. The Resuspension Potential Measurement gives unbiased and reproducible information on the discolouration risk. This methodology is used to assess the efficacy of the flushing program of the Water Company of Limburg in the Netherlands (WML). The program is followed with an extensive measuring campaign involving 701 RPM measurements at more than 120 locations. The adverse effects of cleaning of ferrous pipes were observed in the period immediately following the cleaning. This effect was neutralized within a year which led to the conclusion that water flushing is practically as effective in ferrous pipes as it is in non-ferrous pipes provided that the operational boundaries are met on velocity, volume and order of flushing.

In recent years Italian water utilities have gone through a restructuring process which focus is on processes optimization. Nowadays, the industry is still seeing many mergers and cost-reduction strategies taking place. Due to low tariffs, the Italian Water Industry has very limited economic resources that need to be spent optimally. In this framework, the importance of optimal asset management is increasing: as the budget is limited, an asset-specific knowledge is required "to choose exactly the right assets, to optimize maintenance activities and to refurbish and replace the selected assets at just the right times in a cost-effective manner". This paper introduces the methodology that was developed to reach this objective by HERA, combining the results of a criticality analysis, performed through a detailed hydraulic model, with a Mean Time To Failure analysis based on pipe bursts-leaks data collected during a six-year period and processed in a GIS software.

Without a well designed and implemented Infrastructure Asset Management Strategy (IAM), water service providers will be constantly faced with disruptions in their ability to ensure a continuous and reliable supply of clean and safe water. A key component of IAM is pipeline integrity management. The repeat occurrence of pipeline failures in water supplies is an area of concern for the water industry. South Africa does not differ much in risk from the rest of the world due to the poor state of its water pipelines and a lack of understanding of infrastructure asset management. Ageing networks and the lack of asset management strategies at many water utilities and municipalities are the main reasons for the pipe bursts and an inability to supply water. In terms of pre-stressed concrete pipelines, previously, little information was available about the extent and rate of deterioration of the pre-stressing wires in pre-stressed concrete pipelines. Technological innovations have paved the way for improved inspection, monitoring and management of pre-stressed concrete pipelines. Recent developments in electro-magnetic inspection e.g. Eddy Current scanning technology has proved to be a huge success in terms of determining the number and position of wire breaks in pre-stressed concrete pipelines. Managers now have a greater level of information regarding the integrity of the pipeline and through ongoing monitoring can make more informed decisions by monitoring and analyzing trends. While non-destructive technologies e.g. Eddy Current Scanning represents the most accurate means of determining the integrity of the pipeline, operational challenges prevent a more regular means of assessing its integrity. As such, there is a need for the use of non-interruptive technologies to assess the risk of the probability of failure. Non-interruptive acoustic technology (which includes leak detection and fiber optic monitoring) as revolutionized the manner in which pre-stressed concrete pipelines are managed. Current research and development activities are now focused on the development of a fibre optic monitoring system which will provide real-time information regarding the integrity of the pre-stressed concrete pipeline. Finally all data collected through all monitoring technologies and applications are integrated into a web-based risk model to provide an indication of its current condition, enhance management of the pipeline thereby facilitating informed decision making.

This paper describes the steady progress that the South African Department of Water Affairs and Forestry (DWAF) has been making with formulating a national water services infrastructure asset management (IAM) strategy. A "scan" of the state of water services infrastructure and the state of its asset management, is long complete. This was followed by a process of identifying elements needed for an enabling environment to ensure sound asset management. Since then DWAF, with the assistance of an external team, has been identifying priority strategic actions, taking cognizance of its mandated responsibility and what it needs to do within its own sphere and also in conjunction with others, particularly with other national government departments. DWAF's efforts complement and are complemented by other national IAM initiatives.

It has been estimated that replacement of drinking water infrastructure will need to increase from the current estimated replacement rate of 0.3 percent per year to 2.0 percent per year by 2040 in order to meet the needs of US drinking water utilities. This is approximately four times the current replacement rate. In addition to maintenance, structural and regulatory issues, there is concern over the ability of US drinking water distribution systems to maintain water quality to the consumer. Consequently, drinking water utilities are increasingly interested in the potential for the application of techniques such as Condition Assessment (CA) methodology for managing drinking water infrastructure. The USEPA has therefore initiated a project (carried out by the Eastern Research Group) with the goal of developing new CA techniques that can assist utilities in dealing with some of these issues. Several tools have been developed (which will be discussed) including a modeling approach that can be applied to a drinking water utilities break and leak database and that will help managers understand the factors affecting the "survival" of drinking water pipe sections. The model is based on the application of the Cox Proportional Hazard Model (CPHM) modified by a frailty function. Shared frailty represents unobserved external factors, known to be important, which vary randomly and which are more consistent among sections in the same pipe run than among sections in different pipe runs. Examples of factors which may be represented in this way are soil corrosivity, variations in external mechanical loading, pressure transients, vibration, nearby construction, etc. The CPHM has been applied to a pipe break data base collected by the Laramie Water Utility (located in Laramie, Wyoming (USA)). Preliminary results, for example, indicate that, on the average, metallic pipe has fewer beaks than Poly Vinyl Chloride (PVC) pipe but is more subject to undefined random factors. That is, metallic pipe has more "random frailty" then PVC pipe. This has implications for infrastructure management policies such as the application of advanced monitoring techniques and replacement strategies. In addition to the CPHM for individual pipe sections a general pipe break model has been developed.

In the Netherlands the condition of cast iron (CI) pipes is assessed using destructive techniques (Rosenthal and Slaats, 2000). Consequently, CI pipes are normally inspected only after failure, and the assessment is limited to small sections of the worst affected pipes. Due to the irregular pattern of deterioration of cast iron pipes, the overall condition of a distribution network cannot be based on results from destructive inspection. Non-destructive inspection techniques have multiple advantages. Firstly, the condition assessment takes place on the whole length and circumference of the pipe. Secondly, water supply can in most cases continue undisturbed during the inspection. And, finally, there is no need to dig up the pipe or take samples out of it. To gain better understanding of the possibilities and difficulties, research on various non-destructive inspection techniques is being conducted in the joint research program of the Dutch and Belgian water companies. The Remote Field Technique was applied on a cast iron pipe of the Belgian water company Pidpa during a field test, after which the pipe's condition was assessed with conventional, destructive techniques. The results of both methods are compared and discussed in more detail in this paper. The comparison shows that the Remote Field Technique is both a useful inspection technique (delivering comparable results) and has added value to the destructive technique by showing the deterioration along the length and circumference of the pipe.

Decisions about pipe replacement in water distribution systems usually involve multiple rationales dealing with economic effectiveness, hydraulic consistency and management targets. In addition to these, rehabilitation planning should also take into account the effects on customers of temporary service disruptions during interventions and the potentially achievable leakage reduction subsequent to asset renewal. A multi-objective genetic algorithm is used here to identify a set of "optimal" replacement schemes that consider work allocation based on the position of existing isolation valves and leakage reduction. The effectiveness of ranking of pipes according to their frequency of selection among MOGA solutions in terms of Pareto dominance and practical use for water managers is demonstrated. The benefits of considering segment isolation due to planned/emergency interventions is discussed by comparing solutions obtained with different sets of objective functions. Finally, it is shown that including leakage reduction among the objective functions allows for a faster improvement of network performance in terms of both water savings and average system pressure increases. Analysis is performed on a real medium-size water distribution network.

A Water Distribution System (WDS) that is structurally inadequate in fully satisfying the water required by customers needs to be rehabilitated in order to restore the required performance. However, a problem that frequently arises in this analysis is the selection of which solution should be adopted in order to provide a suitable service and, simultaneously, in minimizing rehabilitation costs. This decision can be facilitated by considering the water required by users but not supplied to them because of the structural inadequacy of the system — representing a source of lost revenue for the water companies. This cost is a function of the level of inadequacy of the hydraulic system and of the unit cost of the water. On this basis, safeguarding the hydraulic reliability of a WDS also implies a reasonable rate of return on the water company's capital investment.

Quantitative risk analysis is used by various water companies, but mainly for aboveground assets for water treatment and pumping. Quantitative risk analysis is less frequently practiced for underground water distribution networks, as the condition of mains and the possible consequences of failures are difficult to predict. Nowadays, quantitative risk analysis for water distribution networks is a logical step forward as more (geographical) information becomes available and links can be made with computer models. Recent research by Kiwa Water Research executed for the Joint Research Programme of the Dutch drinking water companies, made clear that quantitative risk analysis is a feasible method for identifying critical mains sections in water distribution networks. The next step will be to investigate how quantitative risk analysis for distribution networks is to be implemented efficiently.

Development of a methodology, rational and zoning scheme for the demarcation of complicated water distribution networks is important for making the zone demarcation process more accurate, economical, less time consuming, fast, repeatable, generic and optimal with respect to the cost of flow meters required. A new water distribution zone demarcation method is presented that uses the analogy of graph theoretic and graph partitioning principles used in distributed computing to distribute workloads among processors to suggest optimal zoning schemes based on balancing length, demand or flow within zones with the objective of monitoring of unaccounted for water. The method is developed into an automated prototype optimal zoning tool using C++ programming language, a graph partition tool used in distributed computing (METIS) and the EPANET tool kit. The tool is operated by a user interface written in the Python. Case studies are presented to demonstrate how the zoning tool is applied to the zone demarcation problem for the developed zoning schemes. The developed zone demarcation tool was observed to be an efficient and effective approach for the optimal demarcation of complicated water networks into optimal zones based on balancing length, demand or flow within zones. However the tool is sensitive to the number of partitions, the topology of the Water distribution network and the partitioning algorithms used. The tool can be used as a decision support tool for the optimal development and reduction of uncertainties in development of leakage control zones by decision makers. This will enable water companies to increase their productivities and also optimise resource allocations by reduction of the time to monitor, discover leaks and partition zones. This will lead to improved operating revenues.

Despite operational improvements over the last 10–15 years, water utilities still are losing a significant amount of potable water from their networks through leakage. The leakage is managed on the one hand by reactive and proactive maintenance and on the other hand by pressure control to reduce background leakage from connection and joints. This paper is based on experience from the Process Control — Water Software Systems group which was involved in many pressure control projects and the current Neptune project (www.neptune.ac.uk). A fast and efficient method to calculate time schedules and flow modulation curves is presented. Both time and flow modulation can be applied to a single inlet DMA. Time modulation can be applied to a multi-inlet district metering area (DMA) but this is not always possible for flow modulation due to the risk of hunting. It is convenient to distinguish between boundary and internal pressure reducing valves (PRVs), the decision variable for a boundary valve is a PRV set-point whereas for the internal valves it is a valve resistance. The resistance is then automatically translated into a set-point for field implementation.

The quality of Water Distribution System (WDS) models depends on how well they have been calibrated. Calibration of a WDS model with pipes of different age is a complicated problem. The first aim of the paper is to show that the Levenberg-Marquardt algorithm (LMA) may successfully be used for calibration if a correct step along parameters is used for the calculation of partial derivatives. The LMA has been tested on the WDS containing thousands of pipes. Short computer time requirements of the LMA allowed accomplishing more intensive analysis of the WDS. Another aim of the paper is to show that the use of pressure differentials for the calibration of an operational water distribution system will exclude systematic errors, wrong data on elevation of junctions and will significantly eliminate the influence of leakages on calibration. Thorough analysis of the differences between the measured pressures and pressures, calculated by the calibrated model, will allow finding areas with leakages and areas with incorrectly registered demand. Information on the location of leakages in turn will enable to use the optimization procedure for distinction between real losses and apparent losses. This procedure is based on the demands pattern and dynamics of leakages obtained on the basis of pressure dynamics. The information obtained will be used for the new iteration of calibration.

To accurately identify a wide range of parameters is essential for establishing effective hydraulic model of a water distribution system. Although the parameter identification task can be undertaken by using an optimization method such as a competent genetic algorithm as developed in the previous published work by the author, due to a large number of different model parameters such as pipe roughness coefficients, water loss and leakages need to be identified, it is highly likely that the model parameters may compensate one another, thus it is difficult to correctly identify all model parameters. In this paper, a data requirement and usage protocol are proposed and analyzed to minimize the compensation errors. It is applied to the real water distribution systems for both calibrating a hydraulic model and detecting water loss or leakage.

The processes and mechanisms giving rise to failures in repairable systems such as underground water pipes are quite complex and not quite fully understood yet. Therefore flexible statistical models that try to explain these processes are necessary. Data available on pipe breaks is usually poor and left truncated resulting in data sets in which a significant number of pipes have no failures recorded at all. Trying to apply flexible point process models such as the NHPP to such data may limit the ability to adequately capture the failure process. In this paper a zero-inflated NHPP is proposed which tries to deal with such problems. The new model is tested on the real-life pipe data set. The results obtained show that although the zero-inflated NHPP did not outperform the NHPP in general, it provided a better fit to the data and slightly more precise results.

Minimising the loss of treated water from water supply systems due to burst and leakage is an ongoing issue for water service providers around the world. Flow monitoring techniques are currently used by the water industry to monitor leakage, generally offline through the application of mass balance type calculations or through observations of change in night line values. The data for such analysis has, until recently, been at best collected 24 hourly via SMS technology. The objective of the study reported here was to assess the online application of an AI system to a real distribution system and the potential benefits of so doing. Specifically the application of Artificial Neural Networks (ANNs) and Fuzzy Inference Systems (FIS), which are computational techniques in the field of Artificial Intelligence (AI). The online hybrid ANN/FIS system developed uniquely uses DMA (District Meter Areas) level flow data for the detection of leaks/bursts as they occur. The ANN model (a Mixture Density Network) was trained using a continually updated historic database that constructed a probability density model of the future flow profile. A FIS, used for classification, compared observed flows with the probability density function of predicted flows over time windows such that confidence intervals could be assigned to alerts and further, an accurate estimate of likely burst size provided. A Water Supply System in the UK was used for the case study. The case study pilot area has near real-time flow data provided by General Packet Radio Service (GPRS). The online AI leak/burst detection system was constructed to operate along side an existing flat line alarm system, and continuously analyse every twelve hours a set of 50 DMAs of various size, complexity and connectivity within the case study area. Results are presented from a six month period. The new system identified a number of events and alerts were raised prior to their notification in the control room; either through flat line alarms or customer contacts. Examples are given of their correlation with burst reports and subsequent mains repairs. 56% of AI alerts were found to correspond to bursts confirmed by repair data or customer contacts reporting bursts. The study shows that the integration of the AI system with near real time communications can facilitate rapid determination (i.e. before customers are impact) of abnormal flow patterns. It is concluded from the study that the system is an effective and viable tool for online burst detection in water distribution systems.

The water industry in the United Kingdom has been widely criticised for poor performance in detecting and fixing bursts. It is therefore reasonable to question if the current industry approach is adequate. Currently water distributions systems are divided up into District Meter Areas (DMA), typically consisting of around 300–5,000 properties. Ideally each DMA has a single inlet with a flow and pressure meter and a pressure meter at a critical (usually the highest connection) point. Night line flow values are then used as a guide to leakage trends. With reduction in pressure instrumentation costs, improvements in battery performance and communication technologies (such as GSM / GPRS) it is becoming feasible to increase the level of instrumentation deployed per DMA. This paper presents the development of a methodology to explore improving the location of the critical meter point(s) within DMAs for detection of leaks/bursts. The approach is based on running multiple hydraulic model simulations of various burst scenarios. The sensitivity of different monitoring points to the imposed conditions are then evaluated, and the results analysed to select the best point or best combination of two points. Results for the application of the methodology to two real DMA models are presented. These clearly demonstrate the technique's potential to improve the location of the ‘critical meter' for detection of bursts as they occur and the capability for further improvements by increasing the number of instruments is also apparent.

This paper presents the case study of leakage hotspot prediction. This has been achieved by the application of a methodology that has been developed to optimize the pressure dependent emitter locations and demand as possible leakage. A case study is included to illustrate how the optimization modeling can be applied to leakage detection. The application can be used to support traditional leakage detection methods as well as model calibration via an integrated method of simulation and optimization modeling. The results obtained are compared to those obtained from a previously developed method that also identified leakage hotspots in the field. The paper demonstrates that the new approach can be used to reducing the uncertainty of finding water leakage hotspots. It shows that the new method can assist water utilities to reduce field based leakage detection as the method can closely predict the location of many leaks thereby improving leakage detection efficiency.

Studies show that pressure has a major impact on the rate of leakage from leak openings in pipes, and that the leakage exponents in a real network 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 with increasing pressure. In this study, Finite Element Analysis was used to study the relationship between pressure and leak area in different pipes with longitudinal and circumferential cracks. It was found that both longitudinal and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including the loading state, pipe dimensions and pipe material properties. The impact of the different parameters on the pressure-area slope was investigated, and an attempt will be made to find an expression to express the pressure-area slope as a function of the parameters. If such a relationship can be established, it will be possible to predict the behaviour of different types of leak openings in different pipes and pipe materials.

Longitudinal cracks in pipes exhibit expansion under pressure increases due to increased stresses in the pipe walls. The crack expansion increases the leak area and thus the flow rate from the crack. It has theoretically been shown that when tension is applied to a plate with centre crack edges running transversely, compressive stresses occur around the crack. As the stresses reach a certain level, they will cause local buckling of the crack walls, resulting in the opening of the crack. The aim of this investigation is to understand the structural behaviour of a longitudinal crack failure of pipe materials under pressure. This objective is achieved by investigating the structural behaviour of a plate material around the crack and determining the critical stress, thus deriving an equation for the crack opening as a function of pressure and material properties, and subsequently an equation for the leakage behaviour, and establishing a relationship between the crack behaviour of a flat plate and a circular pipe material. A rectangular steel plate with a centre crack is used to investigate the structural behaviour of a pipe material with a longitudinal crack. The results of this investigation will assist in predicting the appropriate leakage equation for pipes.

With an ever-increasing population and a decrease in availability of fresh water, the sustainable and secure supply of fresh water is a growing concern worldwide, and particularly so in South Africa. On-site distribution or plumbing systems have a significant impact on both the efficient use of water and water losses. Metered consumers pay for inefficient use and on-site losses, and thus municipalities are often less concerned about these factors than about losses from their own distribution systems. This project focussed on on-site systems and had two main aims: to determine the fraction of plumbing fittings used in South Africa that do not comply to current legislation, and to determine the extent of losses from on-site distribution systems. Various research methods were employed, including literature reviews, surveys of and interviews with role-players, field investigations and analyses of plumbing replacement programmes. The study found that around 50 % of plumbing fittings installed in South Africa do not comply to legal requirements, and that at least 60% of stands in the Johannesburg area have some on-site leakage present.

The set of equations for solving for pressures and flows in water distribution systems are non-linear due to the head loss-velocity relationship for each of the pipes. The solution of these non-linear equations for the heads and flows is usually based on the Todini and Pilati method. The method is an elegant way of formulating the equations. A Newton solution method is used to solve the equations whereby the special structure of the Jacobian is exploited to minimize the computations and this leads to an extremely fast algorithm. Each iteration firstly solves for the heads and then solves for the flows. In the EPANET implementation of the Todini and Pilati algorithm an initial guess of the flows is based on an assumed velocity of 1.0 fps (0.305 m/s) in each pipe in the network. Each flow is then determined from the continuity equation by multiplying the assumed velocity by the area. Usually velocities in pipes are in the range of 0.5 to 1.5 m/s (and perhaps sometimes higher up to 3 or 4 m/s). Thus the velocities to be solved for are all of the same order of magnitude. In contrast, the range of discharges may be quite large in a system — ranging from below 10 L/s up to above 700 L/s — thus possibly three orders of magnitude of difference. As an alternative to the usual formulation of the Todini and Pilati method in terms of flows and heads, this paper recasts the Todini and Pilati formulation in terms of heads and velocities to attempt to improve the convergence properties. Results are compared for the two formulations for a range of networks from 553 to 10,354 pipes. Convergence criteria for stopping the iterative solution process are discussed. The impact of the initial guess of the velocities in each of the pipes in the network on the convergence behavior is also investigated. Statistics on mean flows and velocities in the network and the minimum and maximum velocities for each of the example networks are given and finally operation counts are also provided for these networks.

In a water distribution system (WDS), low pressure situations can arise for a variety of reasons. For example, over time, the demands may exceed the capacity of the WDS or some major components e.g. pumps and trunk mains may not be operational while repairs are carried out. The extent to which demands are satisfied in a WDS is governed by the actual amount of pressure in the system and pressure-deficient operating conditions are not uncommon. Despite this, the conventional modelling approach works well only under fully satisfactory pressure regimes, with results for subnormal pressure conditions often being inaccurate, misleading and even unreasonable. Sample results for a prototype FORTRAN computer program which can perform head-driven analysis using a globally convergent Newton-Raphson scheme are presented. Extensive testing has shown that the program is efficient and robust. It is demonstrated here that head-driven analysis is not computationally more time consuming than demand-driven analysis and that different functions for head-dependent nodal outflows can produce significantly different results.

Losses from water distribution systems are reaching alarming levels in many towns and cities throughout the world. Leakage represents a large part, frequently more than 30 %, of the water supplied. One of the major factors affecting leakage is pressure in distribution systems. Consequently, it is important to model the hydraulics of water distribution systems with pressure-dependent leakage included. The objective of this paper is to present and validate an improved formulation of the hydraulic network equations that incorporates pressure-dependent leakage. Particular effort has been made to assess the magnitude of the different terms in the equations, including leakage, inertia and head loss. Moreover, a comparison with an extended period simulation model is performed to determine the impact of pressure-dependent demands. The formulation was derived from the Navier-Stokes equations. A system of partial differential equations is solved using a finite-difference method. The feasibility of this method and efficiency of the proposed algorithms are illustrated using a number of case studies.

Stream processing is a relatively new form of programming that employs a GPU (graphical processor unit) instead of solely relying on the CPU (central processing unit). Conventional programming uses the CPU to solve problems in a sequential manner. This is not very effective in solving simultaneous equations quickly. Recently, techniques have been developed that allows a GPU to be used to solve non-graphical mathematical problems. Standard GPUs being used today have over 100 threads compared to the 2 threads typically available to CPUs. Thus certain problems can potentially be solved at substantially higher speeds. The set of equations describing water network hydraulics often contains thousands of equations, which are nonlinear and have to be solved using an iterative process. This problem is potentially well suited to stream processing. However, the Cholesky method (a variant of Gaussian elimination tailored for symmetric positive definite matrixes) currently employed in network solvers is not well suited to stream processing, and an alternative matrix solver is required. The Jacobi iteration method has been identified as a suitable replacement, since each of its coefficients is treated independently of the other coefficients when solving the matrix. While work is still in progress, the potential for significant increases in the speed of solving water distribution hydraulic equations is already apparent.

Difficulties of simulation in existing hydraulic models arising from combinations of pressure and flow controlling devices in water distribution systems have been discussed in a number of previous papers. For instance, examples for non-convergence or wrong results of the hydraulic solver EPANET (version 2.00.10) were first published by Simpson in 1999. It may be shown that the problems were caused by a singularity of the equation system that appears if in an iteration two interacting control devices are active at the same time. In terms of graph theory the part of the network between the two active valves in this case is disconnected from the rest of the system leading to the singularity. In the new EPANET version 2.00.12 that has been released recently this problem is tackled by adding a virtual coefficient to all matrix columns and rows corresponding to nodes of active flow control valves. Mathematically this method is equivalent to adding a very small diameter pipe to the actual network in parallel to the FCV resulting in a nonsingular system. The examples of networks published by Simpson (1999) where EPANET 2.00.10 failed to converge or converged to wrong results now can be solved successfully. Nevertheless the latest release of EPANET still has difficulties in modeling of combinations of control devices. Whereas the former version of EPANET (version 2.00.10) often failed to calculate the correct valve states (active, closed, open) the problems of the new version consist of numerical inexactness that is caused by the addition of the virtual matrix terms for FCVs. In addition examples can be found where version 2.00.12 of EPANET still fails to converge.

Water distribution system modelers organize system models by balancing model complexity and the effort to set up, solve and calibrate the model. The modeling goal is to represent the true system in the field with the least effort and calibration data. As a model increases in complexity as measured by the number of nodes and pipes, more field data is needed to estimate model parameters and the error associated with that model error increases. On the other hand, a simplified model may not capture the full system under all conditions. In terms of water quality, prevailing thought is that an "all-pipe" model is necessary. Here we examine the use of hydraulic equivalent systems on water quality estimates as represented by water age. A simple system is used to demonstrate the effect of applying existing series and parallel pipe simplification approaches. Although these methods preserve pressure conditions, water age is not and increasing levels of system reduction results in larger errors. We then demonstrate that a two step process can insure hydraulic and water quality equivalence for the full range of flows. This study demonstrates that a model skeletonized based on hydraulics to remove or reduce pipes must be recalibrated for water quality at each level of model simplification.

This paper presents a methodology that uses the concept of resilience to generate skeletonized or reduced models of Water Distribution Networks (WDN) with a significantly smaller number of pipes in comparison with the prototype, but that still can simulate, in a very precise manner, the hydraulic and water quality characteristics of the real network. In order to do this, the effect of each pipe on the Resilience Index of the entire WDN is evaluated under hydraulic design conditions. Next, the network is skeletonized by removing from it those pipes with the minimum impact on the Resilience Index, assuring that all consumption nodes are still connected. In order to guarantee that non permanent water quality parameters (i. e. residual chlorine in consumption nodes) of the prototype are adequately reproduced by the reduced model, a correction formula for the bulk and wall coefficient, that control chlorine decay in WDN, was developed; depending on the distance of each pipe to the reservoir or supply source, the correction factor applied to its bulk and wall coefficients is different. The proposed methodology was applied to three WDN and the results obtained are satisfactory: the skeletonized models are able to reproduce the hydraulic behavior and residual chlorine of the entire WDN with high accuracy.

The issue of detecting topological changes in pipe networks due to failing pipes is an important one, especially when performing reliability analysis of a water distribution system. This manuscript presents an improvement to a recently published algorithm, which used the pseudo-inversion of a system model matrix in order to solve a special linear version of a network simulation model for identifying the disconnected nodes. The new algorithm is based on the Cholesky incomplete factorization of the relevant system matrix. The improved algorithm is capable of automatically identifying nodes/pipes disconnected from the water source(s) in large networks. The algorithm is tested and verified on a case study involving a large network derived from a real-life system. The case study results clearly demonstrate the increased computational efficiency and the robustness of the improved algorithm when compared to the previously published one.

As application of hydraulic and water quality modeling of distribution systems continues to increase, there is a need for guidance on best practices for developing, calibrating and using the models. Data collection technologies are rapidly evolving with the implementation of GIS and SCADA systems at many US water utilities. While many utilities are developing and using skeletonized and all-pipes hydraulic models, relatively few have fully implemented more advanced applications like water quality or real-time modeling. The use of advanced optimization algorithms for design and calibration applications remains largely in academia at this time. In a project sponsored by the American Water Works Association Research Foundation (AwwaRF), we have worked with industry leaders and academic partners to develop guidance on current modeling practices. This guidance covers the gaps between textbooks and real-world modeling applications, aimed at providing practical and helpful advice for modelers ranging from beginner to advanced levels. This paper will include discussion of the development of guidance for model input data, calibration data collection, and goodness of fit for calibration. These criteria were developed for models in several categories: master planning, water quality, and advanced applications. A Model Planning Matrix was developed to assist utilities in understanding the range of options for data collection and calibration for each model application category. This matrix provides a linkage so that users can understand how lack of data or poor calibration could impact the ability to use the model for different applications. Furthermore, the range of options provided in the matrix allows users to determine where additional investment in data collection or model calibration could increase the quality of the model for the desired application.

Hydraulic models are used widely to simulate the hydraulic performance of water distribution systems in both design and operational stages. These models have a significant role on decision making procedures. It should be noticed that the quality of model outputs are directly related to the quality of input data. However, because of several reasons such as change of pipes friction factors and diameter, nodal demands, etc., the output results are error prone. On the other hand the design's criteria may be changed during operational period. Therefore, to improve the model performance and reduce the uncertainties during different consumptions procedures, it is necessary to calibrate these models. At the moment just a few commercial models such as WaterCAD which requires a considerable money expenditure are capable of calibration calculations (considering pipes friction factors or just nodal consumptions as the variable), besides the hydraulic analysis. In this research considering an optimization procedure using Genetic Algorithm, a computer code is prepared and linked to the hydraulic simulator (herein, EPANET) to calibrate the model. In this method some variables are considered: pipe friction factor (Hazen William Coefficient), nodal consumptions, combinations of both and pipe diameters. Finally to evaluate the advantages of the proposed methodology a test network is considered and the method is applied for different consumption scenarios.

The theory of unsteady pipe flow and the characteristic method are applied to solve the transient flow equations for transient flow modeling in water distribution systems (WDS), for the purpose of pipe failure prediction and prevention. Based on the investigations on the pipe strength and the pressure measurements with transient flow in pipes, hydraulic safety appraisal system based on transient flow modeling is put forward to predict the water pressure changes caused by the transient flows in the WDS. The characteristic method is improved for transient flow simulation in the complex water distribution systems by optimizing the time step and modifying the friction model, and the results show a feasible oppotunity for engineering application in operational safety management of urban water systems. A method of point rating is firstly applied in the model, and the principles of analysis boundary conformation according to different types of pipeline systems is established and the topologic structure and the date of the steady model is extracted to realize the simulation of the transient flow in complex water distribution systems.

The paper deals with resonance phenomena occurred at the downstream end of a long pipe in a water supply system realized in Northern Italy. The involved pipe connects a large artificial reservoir with a group of storage tanks; it is about 30 km long and conveys water by gravity with a difference in level of 104.5 m. At the downstream end, just before the arrival in the storage tanks, the pipe is subdivided in four branches (a "comb" distribution pipe); two water hammer preventing valves and a regulating valve are installed on each branch. During the closure operation, in certain conditions, a severe pressure oscillation with high frequency and increasing amplitude was observed, suggesting the occurrence of a resonance phenomenon; it caused ground vibrations along the conduit path, also at a large distance from the valve chamber, and damages to the water hammer preventing valves.

A methodology for determining the wall condition of water pipelines, by using an inverse transient model to interpret the measured response of the pipeline to deliberately induced controlled transients is presented. Changes in pipe wall lining and thickness theoretically give rise to reflections in measured transient responses and these can be interpreted to assess pipeline wall condition. The results of field tests on a 750mm diameter pipeline, containing reflections from a damaged section of pipeline, are presented. A distribution of known damage (determined from CCTV camera footage) and inferred damage is characterised in terms of four categories of wall deterioration. This distribution of damage is then included in a transient model of the pipeline and the measured and predicted reflection response are found to compare favourably. The transient model is then combined with a Genetic Algorithm and inverse transient analysis is performed using transient data generated from a distribution of known, inferred and arbitrary damage. The inverse transient analysis relatively accurately predicts the pre-determined distribution of damage along the pipeline.

Hydraulic analysis of a new water supply pipeline in Heilongjiang Province of China has been performed. The study consists of an appraisal of the hydraulic behavior under the steady state hydraulic analysis during the system operation and evaluation of transient conditions during the operation stoppage. Firstly, the steady state analysis is carried out. And then, the transient analysis is implemented by using the Method of Characteristics (MOC). Moreover, the Lattice Boltzmann Method (LBM) is presented as an alternative approach to modeling water hammer. The steady state analysis provides the basic framework for understanding the normal operational behavior of the pipeline. The results demonstrate the reasonable control of some valves will improve the resistance distribution along the pipeline. However, results of transient analysis are significant for individuals involved in making operational decisions of the pipeline to enhance their understanding of the behavior of the system during transient conditions. Furthermore, the accuracy and efficiency of the LBM is numerically investigated. The results indicate that the LBM is more efficient than the MOC.

Closed valves are recurring problems in water distribution systems (WDS). Valves closed during normal exercising or by contractors during construction or system maintenance are not always reopened. The existence of a closed valve not only reduces the operation efficiency, but also can cause severe safety problems when a fire occurs. A methodology to detect closed valves using reflected transients in a full hydraulic transient analysis is presented here. A valve closure varies a pipe's flow rate and often causes an immediate change of pressure and pressure transient. If the valve closure is completed somewhat slowly, a transient with a non-harmful peak is generated but a measurable signal. The premise of this methodology is that in the WDS the reflections of the pressure wave will be altered by a closed or partially closed valve. We begin with a paper study that considers that only one valve is improperly closed. The most likely locations of the closed valve are identified by enumeration. Comparisons between computed and "measured" pressure signals are made using the root mean squared error. Measured signals are developed from numerical model results with random generated measurement errors. A hydraulic transient model based on Chen (1995) is used to compute and analyze transients. Ongoing work is investigating the effect of the number of pressure meters, valve location and valve closure rate. Further work will examine cases with multiple closed valves including optimization methods for alternative optimization algorithms, objective functions and other pattern matching approaches.

Water quality failures in the developed world occur primarily in drinking water distribution systems in rural or small communities. Increased water system monitoring through the use of information technologies, such as sensors and SCADA systems, can reduce the risk of undetected water quality failures and support small utilities in keeping abreast of increasing regulatory stringency. However, because of financial constraints, rural utilities may be particularly susceptible to some of the shortcomings associated with these technologies, such as false readings and data corruption. Bayesian Belief Networks (BBNs) are proposed as a means to integrate sensor information with other operational information to mitigate technological shortcomings and increase certainty about the state of a given drinking water system. The methodology used to develop the BBN for a case study system is discussed in detail.

Heightened concern over potential acts of sabotage against water distribution systems is imparting greater importance to the conceptualization of contaminant migration and the value of simulating contaminant dispersion scenarios which are as realistic as possible and improve the safety of water distribution networks. A typical urban water distribution network presents various scenarios of pipe aging, leakage, etc., that heighten the uncertainty surrounding potential impacts of network contamination, sometimes biasing efforts undertaken by water companies to guarantee a standard quality of potable water. Modelling potential contamination of water distribution systems offers three main advantages: (1) assessment of how dramatically the situation can evolve after a nefarious action or accident, (2) guidance on how to strategically implement a warning system for revealing any dangerous contamination and (3) planning support for the maintenance of those pipes which bear an influence on diffusion and compromise network safety. In this paper, a pressure-driven algorithm with an embedded leakage model is joined with the contaminant decay model of EPANET 2 and is applied to a case study of a real water distribution network. In particular, the tested network represents a typical urban-scale scenario, where different types of users, such as domestic, industrial, commercial and public coexist.

Many of the streams and rivers in the U.S. are sources for drinking water. Water from these surface sources are processed and distributed through pipelines throughout cities and suburbs. Waste water is gathered with a second set of pipelines and treated; and, with the rain waters that wash buildings, malls and streets, is disposed of in the same streams and rivers. The streams and rivers, and treatment and pipeline systems are each critical elements of water infrastructure. Elements of the water infrastructure are hydrologically connected allowing for an examination of such matters as disposal of contaminated drinking water and contamination of streams and rivers from untreated waste water. In a case study, we have "connected-the-dots" in these three infrastructure components (surface water, drinking water, waste water) to better understand and design networked systems that are both robust to variations in the components (including localized failures) and secure against hostile intent.

Though hydraulic models are widely used to simulate contamination events in drinking water distribution systems, the use of similar tools to study the movement of contaminants within buildings is very limited. This paper describes the use of standard EPANET models of selected residential and commercial building types to assess their vulnerability to contamination of the drinking water supply resulting from events occurring within the distribution system feeding the buildings or from within the building itself. This analysis is applicable to either accidental contamination events such as cross connections within the building or intentional contamination events. Hydraulic models representing a typical high rise building and a single-family residence were constructed. The residential model includes all piping in both the cold water system and the hot water system. The high rise model includes the pumping system, tanks, check valves, major vertical backbone piping and a skeletonized representation of the delivery pipes on each floor. Both models are applied in extended period simulations and the movements of both internally and externally generated contaminants are traced through the buildings. Issues that are discussed include: representation of demands, level of skeletonization, operating rules, hydraulic and water quality time steps, potential contamination of the distribution system itself, and future applications of high resolution hydraulic models for human exposure assessments.

This paper describes a new water-quality model that allows incomplete mixing at pipe junctions in water distribution networks. The bulk advective mixing (BAM) model honors momentum transfer and separation of impinging fluid streams within a cross junction. The solution is predicated on observed flow patterns in computational fluid dynamics simulations, which were confirmed by experiments, and a mass balance that ensures solute mass is conserved. This paper focuses on the implementation of this new model in EPANET, software that models hydraulics and water quality in water distribution networks. In the new version, EPANET-BAM, a mixing parameter, s, is implemented that allows the user to select the bulk advective mixing model (s = 0), the existing complete mixing model (s = 1), or a result that is linearly scaled between the results of the two models. Aside from the mixing parameter, which has been added to the junction property field within EPANET, all other functions of the BAM model are transparent to users of EPANET-BAM. This paper presents an example of the use of EPANET-BAM and the potential impact of the new model on water quality predictions and risk assessments.

Investigation of turbulent mixing in pipe joints has been a topic of recent research interest. These investigations have relied on experimental results with downstream sensors to determine the bulk characteristics of mixing in pipe joints. High fidelity computational fluid dynamics models have also been employed to examine the fine scale physics of the mixing within the joint geometry. To date, high resolution imaging of experimental conditions within the pipe joint has not been reported. Here, we introduce high speed photography as a tool to accomplish this goal. High speed photography applied to clear pipe joints with the necessary image processing can provide qualitative and quantitative insights into mixing processes. A limitation of this approach is that it provides two-dimensional images of a three-dimensional process.

Municipal water distribution networks consist of numerous cross-, tee-, and wye- junction connectors. In recent years, a series of experimental and numerical studies have sought to understand solute mixing at a cross junction. To address solute mixing phenomena at cross junctions, a fully functional computer program (AZRED v.1.0.0) was developed based on experimental results. The code was validated using a set of network-level experimental data. In the present study, comprehensive solute mixing patterns are investigated for various combinations of cross, double-tee, and wye junction connectors with different flow directions. Mixing patterns for various junction configurations are also visualized by means of dye injections at different flow ratios. These findings are integrated into a water quality solver (AZRED v.1.1.0) suitable for large-scale network simulations. Improved water quality models will be crucial in identifying optimal locations for water quality sensors, assessing models for early warning systems, and generating the exposure information needed for quantitative risk assessment.

Water quality models for municipal pipe networks commonly use the plug flow assumption to calculate axial mass transfer for all flow regimes. Classical works on axial dispersion, conducted five decades ago (Taylor's theory), laid foundations that have been examined and applied to chemical and industrial processes for laminar and turbulent flows. However, these experimental findings have not been fully integrated into water quality models for pressurized water distribution systems. The plug flow assumption often leads to discrepancies when compared to experimental or field data in unsteady low flow (laminar and transitional) zones of municipal pipe networks. The present study examines the axial dispersion of a non-reactive tracer in a pipe under laminar and transitional flow conditions. Inlet concentration readings are used as upstream boundary conditions for Computational Fluid Dynamics (CFD) simulations and ID Advection-Dispersion (AD) models. The resulting downstream concentrations are compared with analytical approximations to determine the reliability of each approach. The present work will improve our fundamental understanding of solute transport and enhance our ability to model and predict water quality in municipal distribution systems. Improved water quality models with accurate spatio-temporal axial dispersion patterns will be critical in optimizing water quality sensor placement, assessing models for early warning systems, and generating the exposure information needed for quantitative risk assessment.

It has become generally accepted that water quality can deteriorate in a distribution system through reactions in the bulk phase and/or at the pipe wall. These reactions may be physical, chemical and/or microbiological in nature. Perhaps one of the most serious aspects of water quality deterioration in a network is the loss of the disinfectant residual that can weaken the barrier against microbial contamination. Studies have suggested that one factor contributing to the loss of disinfectant residuals is the reaction between bulk phase disinfectants and pipe wall material. Free chlorine loss in corroded metal pipes, subject to changes in velocity, was assessed during an experiment conducted under controlled conditions in a specially constructed pipe loop located at the U.S Environmental Protection Agency's (EPA's) Test and Evaluation (T&E) Facility in Cincinnati, Ohio (USA). These studies demonstrated that in older unlined metal pipes, the loss of chlorine residual increases with flow. Additional experimental studies are currently being conducted by the USEPA. They are intended to study the effect of hydrodynamics on disinfectant residual wall demand as well as the effect of total organic carbon, initial disinfectant levels, and pipe materials on chlorine and chloramine decay and disinfection by-product (DBP) formation. These experiments are being conducted in parallel using both unlined metallic and new polyvinyl chloride (PVC) pipe. The first phase of these experiments (which will be reported here) has focused on the effect of flow rate and pipe materials on the loss of chlorine disinfectant residuals. Results from these studies indicate that there is significant disinfectant wall demand in unlined metallic pipe even under stagnant and laminar flow conditions and that increases in flow rate can increase this demand. Wall demand in the PVC pipe, however, was found to be virtually nonexistent. Studies were also conducted on the rate of trihalomethanes (THM) formation under stagnant, laminar, transitional and turbulent conditions. Planned experiments include studies on chloramines and further attempts to isolate the effects of materials on disinfectant reaction kinetics. It is believed that results from these studies can be used to develop strategies to help maintain adequate disinfectant levels in distribution system networks.

Accurate prediction of chlorine residue concentration has become one of the most important tools for water quality modeling and management in water distribution systems. Although former researchers used genetic algorithm (GA) solver to calibrate relative parameters, it was found difficult to apply this method in large-scale water distribution systems due to its long computational time. In this paper, the chlorine decay rates in the wall reactions within the pipes are calibrated dynamically by a new combined optimization algorithm of CORS-RBF-GA. The CORS-RBF-GA algorithm takes CORS (Constrained Optimization using Response Surface) as the whole optimization framework, RBF (Radial Basis Function) as a surrogate of the water quality detailed model, GA as RBF optimization solver. The computational time of water quality modeling and simulation of water networks is reduced four times. One engineering case study is also presented for testifying this method, followed with more efficient and promising results of chlorine residue simulations, comparing with the field measurements.

UV irradiation has become a common technique for drinking water disinfection since it was demonstrated to be very effective against (oo) cysts of Cryptosporidium and Giardia. One of the most important factors which limited UV applications in drinking water treatment was that it had no long term disinfecting effect in a distribution system. The results showed: (1) UV disinfection alone, did not impact the biofilm densities of steady-state significantly. The biofilm densities for the un-disinfected system were similar to the UV disinfected system, and it needed only 2 days to achieve steady-state, which was shorter than the UV disinfected system of 6∼8 days. (2) The bulk fluid concentrations and biofilm densities increased equally in the first few days of operation, and it increased with the biofilm densities decreased in steady-state. (3) It was considered to have biostability in a model distribution system when the chlorine dosage was above 0.7 mg/L in the experiment. The impacts of chloramine dosages on biofilm densities were not as significant as that of chlorine dosages. To add 0.4 mg/L chloramine had a similar effect as to when the chlorine dosage was 0.7 mg/L. Thus chloramine might be a more appropriate additional disinfectant after UV. (4) The biofilm densities and residual chlorine had a certain linear relationship. This also related to the bulk fluid concentration. The residual chlorine had more control effects when added chlorine than chloramine. The biofilm could keep growing with low residual chlorine.

Single- and multi-objective sensor network designs have relied on water quality models that assume instantaneous and complete mixing of species at junctions. However, recent findings show that the perfect mixing assumption at pipe junctions potentially results in erroneous outcomes in predicting water quality in pipe networks. The latest studies, through a series of computational and experimental approaches, provide a higher-accuracy water quality model. In the present study, sensor network designs in water distribution networks are reexamined using both the perfect mixing and non-perfect mixing assumptions. The optimization algorithm minimizes the number of sensors needed for detecting potential contaminant intrusions at all the nodes (100% detection coverage), while maximizing the redundancy of sensor coverage. Extended-period simulations of a set of contamination events were performed on two water quality models and resulted in two distinct contamination-event matrices. Comparisons of the required number of sensors and corresponding locations indicate that incomplete mixing at pipe junctions has a significant impact on the optimal sensor placement. Therefore, the improvement of water quality modeling will improve the effectiveness of early warning detection systems in the event of accidental or deliberate contamination.

The City's water distribution system supplies a population of 76,000 from seven groundwater wells without using any chemical constituent. On August 27, 2007 an emergency chlorination test was conducted for two weeks by injecting chlorine to the distribution system. The objective of this chlorination test was to determine if enough chlorine residual can be observed in the whole distribution system in the event of a contamination. The first step of this study was to build the water quality model with the kinetic reaction parameters. Based on the model predictions from two demand scenarios (Average Day Demand and Maximum Day Demand), a set of 49 sampling locations was proposed prior to the test to ensure that chlorine is properly propagated in the entire system. The field measurements collected during the chlorination test show that 68 % of the sampling locations received the chlorinated water within 24 hours, 90 % of the sampling locations received the chlorinated water within two days, and 100 % were covered in four days. The model predictions were fairly accurate as the simulation results showed that between 56 % and 75 % of all the junction nodes will receive the chlorinated water within one day, and 95 % of all junction nodes are covered in four days. Several sampling locations situated in the Fairfield Island area with measured water age over 72 hours can still have chlorinated water within 24 hours if three hydrants flowing at 60 L/s are opened for 24 hours. The chlorination system can thus be used as an emergency standby system with the capability to effectively disinfect the entire system in the event of an emergency. This study demonstrated that a complex water quality network model can be used as a practical tool for the planning of sampling design to meet water quality requirements.

Contamination warning systems (CWS) are a promising approach for detecting contaminants in drinking water systems in time to allow for the effective reduction of public health or economic impacts. In this work, the authors utilize TEVA-SPOT, the Threat Ensemble Vulnerability Assessment and Sensor Placement Optimization Tool, to address one of the most significant outstanding questions about sensor network design: how many sensors are needed in a water distribution system to reduce the risk of contamination incidents? Previous work has assumed that the number of sensors was determined prior to optimization for the best locations, and was typically limited by budget constraints. In this paper, the authors use network models for several different water utilities that range in size from small to large systems. Sensor network designs are developed that minimize several objectives of concern to water utilities. The number of sensors needed is a question of acceptable risk and is shown to be dependent on the detection goals of the community, utility-specific hydraulics, the sensor technology, and the speed at which an effective emergency response can be achieved. The implications of these results to the widespread applicability and sustainability of CWS will be discussed.

With growing concerns related to potential contamination ingress via backflow and/or terrorist threats to drinking water, useful methodologies are needed to assist in identifying locations from which ingress may have occurred. An efficient data mining approach in conjunction with a maximum likelihood procedure is described, which provides a means to identify the location and timing of an intrusion event, based on limited sensor data. The effectiveness of the data mining method is demonstrated using a case study network where it takes only approximately 5 minutes to identify an injection event using 5 sensors in a 285 node water distribution network. The effectiveness of the method is demonstrated using a number of alternative applications of the data mining methodology, which ensures the robustness of the methodology in locating potential sources of the ingress event.

We provide a preliminary set of results to evaluate a model-based algorithm for detecting anomalous distribution system water quality events in real time. This model-based algorithm relies on a real-time hydraulic and water quality model to estimate the water quality signature, for comparison with sensed water quality signals. The difference between the modelled and the sensed water quality would be processed (e.g., filtered) to detect changes that are inconsistent with noise and thus likely to be associated with a contamination incident. Our preliminary results evaluate the damaging influence of errors in model predictions caused by errors in the estimation of real-time water demands using a predictor-corrector algorithm. For one test network, even when the chlorine predictions are corrupted by significant appears qualitatively different from the noise generated by demand errors, providing hope that such signals could led to improvements in both sensitivity and specificity for event detection.

This paper presents a novel risk-based approach to determine efficiently and effectively the optimal sensor locations to detect contaminants in a water distribution network (WDS). If the contamination is detected in time, it is prevented from spreading through the network and customer safety is ensured. The optimisation task formulated here has two objectives: (1) minimise the risk of contamination and (2) minimise the number of sensors used. The former expresses the likelihood that a set of sensors cannot detect a contaminant and the associated amount of polluted water that is consumed prior to detection, while the latter acts as a surrogate for the sampling design cost. The problem is solved using the NSGA-II algorithm (Deb et al., 2002) assuming that a single contaminant intrusion can occur anywhere in the system at any ten minute time interval during 24 hours. An importance-based contamination scenario selection is used to reduce the computational requirements associated with evaluating a potentially large number of samples and to accelerate the optimisation process while preserving accuracy. The methodology is tested on a benchmark network from the Battle of the Water Sensor Networks held in 2006 (Ostfeld et al., 2008). The results obtained demonstrate that only a small portion of a network needs to be monitored to provide a reasonable amount of safety.

In collaboration with Kiwa Water Research, TNO (Netherlands Organisation for Applied Scientific Research) has investigated the possibilities to detect and classify aberrant sounds in water networks, using acoustic sensors. Amongst the sources of such sounds are pumps, drills, mechanical impacts, which could indicate, for instance, a terrorist's attempt to inject a toxicant into the water mains. In parallel, an important spin-off is recognised in the detection of other sounds, such as those caused by leaks in water pipes and leaking valves. The acoustic water pipe monitoring project was carried out between 2003 and 2007 in three distinct phases: 1). The first phase was carried out in 2003–2004 to gain knowledge on the subject. Models were developed for the sound propagation in water pipes and computer simulations were carried out to specify detection ranges. 2). In the second phase, in 2005–2006, the knowledge created in phase 1 was applied for detection of leakage and terrorist attacks. To this end, a number of field experiments were carried out to characterise background noise and suspicious sounds. It was shown that both leakage and intrusion sounds could be detected up to a range of 100 m in regular 110-mm diameter PVC pipes. At this point, Kiwa Water Research and TNO decided to focus their efforts on terrorist detection in the third and last phase of the project. 3). In the third phase, carried out in 2006–2007, a demonstrator was developed for the detection and classification of aberrant sounds and tested on an operational water supply system. Overall, the TNO acoustic monitoring demonstrator, equipped with two sensors fixed on fire hydrants and two on service taps, has proven to be a suitable and promising system for protection of buildings: it is capable of working in real time and detected about 90% of terrorist intrusion sounds within a range of 110 m (a range suitable for building protection). Using the techniques developed for leakage detection in phase 2, and a similar acoustic demonstrator, the performance of operational systems could further be assessed to detect leakage.