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Valves play a critical role in a water distribution system for subsystem isolation and flow or pressure control. Among them, subsystem isolation is required to repair or to rehabilitate a broken component and can be done by closing adjacent valves. To evaluate the role of valves, the concept of "Segment" is necessary. A segment consists of a set of pipes and nodes isolated together by closing adjacent valves when a pipe fails. An efficient algorithm to identify segments in a water distribution system is proposed. In addition, when a segment is isolated, an additional subsystem may be disconnected from water sources by the segment isolation. It is a topological unintended isolation. In addition, a hydraulic failure, in terms of pressure types of failures at demand nodes should be considered. These three account for the failure impact of a pipe. Placing valves efficiently improves the reliability of a water distribution system. However, the valve reliability itself is not 100%. Therefore, valve failure consequence should be explored in determining the locations of valves. For this purpose, three methodologies, namely segment-valve matrix algorithm, decision tree approach and simulation are proposed. Another consideration for placing valves is a strategic valving rule, namely N and (N-1) valving rules. Using a formulation for node reliability in terms of failing valves, the reliability difference between the two valving rules is evaluated. We also employ a mixed N and (N-1) valving rule. Another strategic valving rule, a segment size reducing approach minimizing the number of affected customers is proposed. The developed algorithms are utilized to build software, the Strategic Valve Management Model, to solve practical problems. The methodology is applied to three real water distribution systems. / Ph. D.

The design of water distribution systems has received a great deal of attention in the last three decades because of its importance to industrial growth and its crucial role in society for community health, firefighting capability, and quality of life. The cost of installing a water distribution system is typically in the tens of millions of dollars. These systems also account for the largest costs in the municipal maintenance budgets. Furthermore, existing systems are being burdened by increasing urban development and water use. All these factors cause the pipe sizing decisions to be a critical task in designing a cost effective water distribution system that is capable of handling the demand and satisfying the minimum pressure head and hydraulic redundancy requirements. A number of research efforts have focused on the least cost pipe sizing decision, each of them generating improved solutions for several standard test problems from literature, but so far, very little work has been done to test the quality of these solutions. In this thesis, two lower bounding schemes are proposed to evaluate the quality of these solutions. These lower bounding schemes make use of the special concave-convex nature of the nonlinear frictional loss terms. We show that the first is a dual to <i>Eiger et al.’s</i> [1994] bounding procedure while the second method produces far tighter lower bounds with comparable ease. Results on applying these lower bounding schemes to some standard test problems from literature are presented. The second lower bounding scheme is then embedded in a branch-and-bound procedure along with an upper bounding scheme by suitably restricting the flows at each node of the search tree. By branching successively, we attempt to narrow the gap from optimality to generate near optimal solutions to the least cost pipe sizing problem. This results in a comprehensive reduced cost network design that satisfies all pressure and flow requirements for realistically sized problems. The proposed method is applied to standard test problems from the literature. It is hoped that this method will provide a useful tool for city engineers to design a cost effective water distribution system that meets specified hydraulic requirements. / Master of Science

Att ha ständig tillgång till ett hälsosamt, rent och gärna gott dricksvatten tas idag ofta som självklart av många människor i Sverige. Sveriges sammanlagda nybildning av vatten innebär idag inga problem för dricksvattenförsörjningen om man bortser från ojämn fördelning av vattentillgångar samt lokala kvalitetsproblem. Många områden förses med dricksvatten från något av landets omkring 2000 vattenverk. En del får sitt vatten från enskilda brunnar, medan vissa har löst vattenfrågan tillsammans med andra i samfälligheter. Vissa samfälligheter som inte har någon egen vattentäkt kan ibland förses med vatten från ett allmänt distributionsnät. I Vaxholms kommun finns nära ett 30-tal samfälligheter som får sitt vatten från Görvälnverket i Järfälla kommun vilket ägs och drivs av kommunalförbundet Norrvatten AB. Behandlat dricksvatten distribueras vidare av Norrvatten AB. I Vaxholms kommun är Vaxholmsvatten AB/ Roslagsvatten AB VA-huvudman och förvaltar kommunens allmänna VA-anläggning. Roslagsvatten AB levererar vatten till vattenkonsumenter som är anslutna till det allmänna VA-nätet i Vaxholms kommun, men bolaget levererar även dricksvatten till nämnda samfälligheter. Vattenverket behandlar (renar) det så kallade råvattnet från vattentäkten (i detta fall Mälaren) för att åstadkomma ett kvalitetsmässigt bra dricksvatten sett ur såväl kemisk som ur mikrobiologisk synvinkel. Kan då dricksvattensamfälligheterna slå sig till ro med att de har ett dricksvatten av god kvalitet? SRMH bedriver kontroll och tillsyn av dricksvattensamfälligheterna och deras distributionsanläggningar. SRMH har gjort sina första pilotinspektioner hos samfälligheterna och uppmärksammat ett antal förmodade brister med vissa rutiner och installationer. I forskningsfältet kring distributionsanläggningar för dricksvatten studeras bland annat faktorer som påverkar mikrobiologisk förekomst och tillväxt i distributionsanläggningar. Mot bakgrund av utvalda delar ur detta forskningsfält har jag skapat ett analytiskt ramverk för att söka värdera mikrobiologiska risker i samfälligheternas distributionsanläggningar. Förutom detta görs några typer av mikrobiologiska analyser för att jämföra med uppskattad risk. Förutom protokoll från SRMH:s inspektioner av samfälligheterna görs små intervjuer av vattenkonsumenter och samfällighetsansvariga. För att se var eventuella kvalitetsproblem uppstår används sekundärdata från Norrvatten som beskriver kvalitet efter vattenverkets behandling och kvalitet vid ett vattentorn på ”halva vägen” samt vid en referenspunkt i Vaxholm. Relevant dricksvattenjuridik studeras också för att ta reda på vem som ansvarar för vad samt för att se vilka kvalitetskrav som är relevanta avseende samfälligheterna. Resultatet antyder försiktigt att riskerna men även vattentemperaturen samt den mikrobiologiska vattenkvaliteten (odlingsbara mikroorganismer) i undersökningen till viss del skiljer mellan olika typer av samfälligheter. För samfälligheter med året-runt-vatten verkar problemen vara mindre, medan för samfälligheter som endast har sommarvatten verkar det finnas fler risker. Det senare verkar även gälla för samfälligheter där fritidsbostäder ingår. Skillnader i antal långsamväxande mikroorganismer mellan olika samfällighetstyper är dock mer osäkra. Kvalitetsreglerna avseende mikrobiologi i samfällighetsnätet och i det allmänna nätet styrs av livsmedelsverkets föreskrifter och EU:s dricksvattendirektiv och alla parter måste försäkra sig om att kvalitetskraven uppfylls inom respektive distributionsnät. Återströmning av vatten från samfälligheter till den allmänna distributionsanläggningen verkar inte kunna regleras av lagen om allmänna vattentjänster och därmed ej heller av det lokala regelverket ABVA för Vaxholm. Enligt min tolkning av regelverket är respektive ägare av distributionsnäten ansvariga för om kvaliteten påverkas i det egna nätet när/om återströmning sker från mottagande part. I diskussionsdelen görs även jämförelser avseende temperatur och mikrobiologiska parametrar mellan de olika typerna av studerade samfälligheter och Norrvattens perifera kommuner för att se om det finns några skillnader. / Continuous access to healthy, clean and good-tasting drinking-water is perceived as obvious for many people in Sweden. The total regeneration of water is currently not a problem in Sweden if uneven distribution and local quality problems are not accounted for. Many regions are supplied with drinking water from one of Sweden’s around 2000 water treatment plants. Other water consumers get their water from private wells, while others get water access via community-owned distribution systems. Sometimes communities that do not have their own water supply can get water supply through a public distribution system. In the municipality of Vaxholm almost 30 small communities get their water from the water treatment plant (WTP) Görvälnverket, which is owned and operated by a municipal association called Norrvatten AB. Norrvatten AB redistributes the treated drinking water. In Vaxholm, Roslagsvatten AB is the legal principal of water and sewage. Roslagsvatten AB distributes water to water consumers in the municipality of Vaxholm. The WTP treats (purifies) the surface water from the water source (in this case Mälaren) in order to provide a good quality drinking water seen from both a chemical and microbiological point of view. Under these circumstances, could the water communities be complacent that they have a good quality drinking water? Södra Roslagens Miljö- och hälsoskyddskontor (SRMH) is the local health protection agency responsible for control and enforcement of drinking water communities in Vaxholm. After having performed pilot inspections at the water communities, SRMH drew attention to some assumed risks and deficiencies with routines and water pipe installations. In the drinking water distribution systems research field, factors influencing microbiological presence and growth are investigated. In the view of selected portions from this research field, I have created an analytical framework to be able to evaluate some kind of microbiological risks in the communities’ water distribution systems. Besides this, some microbiological analyzes are made to compare with assessed risk. In addition to studied protocols from inspections of the communities, some minor interviews are made with water consumers and persons responsible for plumbing in the communities. To assess whether potential quality problems occur, secondary historical quality analysis data from Norrvatten AB is used. Quality data from directly after treatment at the WTP, from a water tower “halfway” to Vaxholm, and from a reference location in Vaxholm is used. Swedish and European Union legal framework of relevance regarding drinking water is studied to find out relevant legal quality requirements with regards to the communities. The result gently suggests that identified risks but also water temperature and investigated microbiological quality (culturable microorganisms; HPC counts, 22 °C, 3 days) in the study to some extent differ between different types of communities. For communities with full-year water supply, the problems seem to be less. On the contrary, for communities with supply only during summer, problems seem to be greater. Problems also seem to exist for communities where holiday residences exist. Differences in the number of slower growing microorganisms (HPC counts, 22 °C, 7 days) between community types is more uncertain. The microbiological quality of drinking water is regulated by Swedish national regulations and by European Union’s drinking water directive. All parties must ensure that quality standards are met in each distribution network. Backflow of water from communities’ distribution networks does not seem to be regulated by the Swedish law on public water services and thus neither by the local regulatory called “ABVA” for Vaxholm. According to my interpretation of the regulations, the respective owners of the distribution networks are responsible for if quality is adversely affected in its own network if backflow occurs from the receiving party. In the discussions chapter, temperature and HPC counts are compared between studied communities and Norrvatten’s peripheral municipalities to assess if differences exist.

Water distribution systems convey drinking water from treatment plant and make available to consumers’ taps. It consists of essential components like pipes, valves, pumps, tanks and reservoirs etc. The main concern in the working of a water distribution system is to assure customer demands under a choice of quantity and quality throughout the complete life span for the probable loading situations. However, in some cases, the existing infrastructure may not be adequate to meet the customer’s requirements. In such cases, system modeling plays an important role in proper management of water supply systems. In present scenario, modeling plays a significant task in appropriate execution of water distribution system. From the angle of taking management decisions valve throttling control and pumps speed control are very important. These operational problems can be addressed by manual control or by automatic control. The problem is the use of manual controls that slow down the effectiveness of the system. It reduces the efficiency of operation of valve or pump. To improve the efficiency of such water distribution systems, an automatic control based technology has been developed that links the operation of the variable speed pump control or valve throttling control. By employing an automatic control, the pump can adjust its speed at all times to meet the actual flow requirements of each load served. In case of real system design Simulink is the most widely used tool. Commercial software package Matlab/Simulink used for creation of WDS model. The goal was to produce a model that could numerically analyze the dynamic performance of a water distribution system. A Comparison of single platform methodology (Simulink based control) and double platform methodology (Matlab and EPANET based control) has been done. Nonlinear Dynamic Inversion (DI) Control system model is developed for WDS model in Matlab/Simulink environment. Controller gain parameters are the very important value in control prospective. If the controller gain parameters are chosen incorrectly, the controlled process input can be unstable, i.e. its output diverges, with or without oscillation Tuning is the adjustment of control parameters (gains) to the optimum values for the desired control response. There are several methods for tuning controller like manual tuning (Trial and error procedure), Ziegler-Nichols method, Output Constraint Tuning (OCT) etc. Establishment of a pump operational policy by which all the reservoirs can be fed simultaneously to meet their requirements without creating undue transients. Tune the gain of DI controllers by different tuning methods and evaluate the best tuning method on the basis of controller performance. Development of meaningful additional objective is search of lower bound pump speed on the basis of control time or settling time. To bring the pump speeds in feasible range, application of constraint in pumps speed is introduced. The magnitude of constraints can be found using Monte Carlo methods. Monte Carlo methods are frequently used in simulating physical and mathematical systems. This method may be the most commonly applied statistical method in engineering and science disciplines. Another benefit is providing increased confidence that a model is robust using Monte Carlo testing. Model development for generalized control system for water distribution network provides the simplification needed for the simulation of large systems. Model development is based on the study of symmetric and non symmetric small, irregular networks, as well as large, regular and open bifurcating water distribution system. The problem considered in this section is that of flow dynamics in simple to complex, regular network which bifurcates in the form of a branching tree. In addition the control application of the flow network is investigated using valves as the manipulated variables to control branch flow rates. Communication between the network hydraulics coming from EPANET and control algorithm develop on Matlab (Programming Language) can be generalized with the help of development of general purpose control algorithm model.

The burdensome capital cost of urban water distribution systems demands the use of efficient optimization methods capable of finding a relatively inexpensive design that guarantees a minimum functionality under all conditions of operation. The combinatorial and nonlinear nature of the optimization problem involved accepts no definitive method of solution. Adaptive search methods are well fitted for this type of problem (to which more formal methods cannot be applied), but their computational requirements demand the development and implementation of additional heuristics to find a satisfactory solution. This work seeks to employ adaptive search methods to enhance the search process used to find the optimal design of any water distribution system. A first study presented here introduces post-optimization heuristics that analyze the best design obtained by a genetic algorithm--arguably the most popular adaptive search method--and perform an ordered local search to maximize further cost savings. When used to analyze the best design found by a genetic algorithm, the proposed post-optimization heuristics method successfully achieved additional cost savings that the genetic algorithm failed to detect after an exhaustive search. The second study herein explores various ways to improve artificial neural networks employed as fast estimators of computationally intensive constraints. The study presents a new methodology for generating any large set of water supply networks to be used for the training of artificial neural networks. This dataset incorporates several distribution networks in the vicinity of the search space in which the genetic algorithm is expected to focus its search. The incorporation of these networks improved the accuracy of artificial neural networks trained with such a dataset. These neural networks consistently showed a lower margin of error than their counterparts trained with conventional training datasets populated by randomly generated distribution networks.

This study gives a description about the development of a computer model, RealPipe, which relates genetic algorithm (GA) to the well known problem of least-cost design of water distribution network. GA methodology is an evolutionary process, basically imitating evolution process of nature. GA is essentially an efficient search method basically for nonlinear optimization cases. The genetic operations take place within the population of chromosomes. By means of various operators, the genetic knowledge in chromosomes change continuously and the success of the population progressively increases as a result of these operations. GA optimization is also well suited for optimization of water distribution systems, especially large and complex systems. The primary objective of this study is optimization of a water distribution network by GA. GA operations are realized on a special program developed by the author called RealPipe. RealPipe optimizes given water network distribution systems by considering capital cost of pipes only. Five operators are involved in the program algorithm. These operators are generation, selection, elitism, crossover and mutation. Optimum population size is found to be between 30-70 depending on the size of the network (i.e. pipe number) and number of commercially available pipe size. Elitism rate should be around 10 percent. Mutation rate should be selected around 1-5 percent depending again on the size of the network. Multipoint crossover and higher rates are advisable. Also pressure penalty parameters are found to be much important than velocity parameters. Below pressure penalty parameter is the most important one and should be roughly 100 times higher than the other. Two known networks of the literature are examined using RealPipe and expected results are achieved. N8.3 network which is located in the northern side of Ankara is the case study. Total cost achieved by RealPipe is 16.74 percent lower than the cost of the existing network / it should be noted that the solution provided by RealPipe is hydraulically improved.

The topic of the thesis is multi objective condition assessment of water supply systems. The state of the art of condition assessment of water supply systems and the state of the art of multi objective optimization methods are presented within the thesis. Based on these recherches, the uniform methodology of condition assessment of water supply systems and its 7 modules was designed. The thesis deals with the selected modules to condition assessment of water pumping stations, water networks and pipe sections. The output of the methodology is the assignment of a category of the technical condition to the rated object. The proposed methodology was tested on real water facilities and proves the ability of a fair presentation of the technical condition of the object.