Journal of Water Resources Planning and Management

The battle of background leakage assessment for water networks (BBLAWN) challenge was approached using successive linear programming. A linear representation was solved successively for the nonlinear constraints of headloss, leakage, pump energy consumption, and pipe sizing. The optimization model returned minimal cost pump scheduling and pipe sizing while minimizing leakage and maintaining minimum service pressures to the consumers. Pressure reducing valves, pump, and water tank sizing were performed manually and their effect was examined using the optimization model. Parallel pipes were added along the main supply pipes from the pumping stations to the water tanks, to allow for minimum service pressures. Pressure reducing valves were added to pipes branching from the main supply pipes to lower excess pressures to the secondary supply pipes.

Optimal management of water and energy resources worldwide is a basis for environmental and socioeconomic sustainability in urban areas, which has become even more relevant with the advent of the smart and water sensitive city paradigm. In water distribution networks (WDNs) water resource management is concerned with increased efficiency, which is primarily related to the reduction of leakages, whereas energy management refers to optimal pump, valve, and source scheduling strategies considering the hydraulic system requirements. These management goals require planning of asset renewal and improvement works in the short time (operational) and medium time (tactical) horizons, considering the financial sustainability of relevant actions. The battle of background leakage assessment for water networks (BBLAWN) was designed as a competition held at the 16th Water Distribution Systems Analysis Conference, in Bari (Italy) in 2014 (WDSA), to address the aforementioned management goals. The teams taking part in the BBLAWN were asked to develop a methodology for both reducing real water losses and saving energy in a real WDN considering the possibility of asset renewal and strengthening. Fourteen teams from academia, research centers, and industry presented their solutions at a special session of the WDSA 2014 conference. This paper briefly describes the BBLAWN and presents one of the solutions provided by the organizers to illustrate the ideas and challenges embedded in the posed problem. The overview of the solutions provided by the participants shows that management decisions need to be supported by engineering judgment and with tools that combine computationally effective multiobjective optimization and hydraulic models capable of assessing pressure-dependent background leakages.

Identification of the optimal rehabilitation plan for a large water distribution system (WDS) with a substantial number of decision variables is a challenging task, especially when no supercomputer facilities are available. This paper presents an initiative methodology for the rehabilitation of WDS based on three sequential stages of multiobjective optimization models for gradually identifying the best-known Pareto front (PF). A two-objective optimization model is used in the first two stages where the objectives are to minimize rehabilitated infrastructure costs and operational costs. The optimization model in the first stage applies to a skeletonized WDS. The PFs obtained in Stage 1 are further improved in Stage 2 using the same two-objective optimization problem but for the full network. The third stage employs a three-objective optimization model by minimizing the cost of additional pressure reducing valves (PRVs) as the third objective. The suggested methodology was demonstrated through use of a real and large WDS from the literature. Results show the efficiency of the suggested methodology to achieve the optimal solutions for a large WDS in a reasonable computational time. Results also suggest the minimum total costs that will be obtained once maximum leakage reduction is achieved due to maximum possible pipeline rehabilitation without increasing the existing tanks.

The paper describes and discusses the application of a guided evolutionary approach for the optimization of water distribution networks. Initially developed for the Battle of the Water Networks II (BWN-II), the approach was adapted and improved for competing in the Battle of Background Leakage Assessment for Water Networks (BBLAWN). The proposed evolutionary approach operates in an exclusively discrete solution space and is intended to require as little engineering judgment and time as possible while attaining acceptable and informative results that are useful for decision making. Its main features are custom crossover and mutation operators specific for water distribution network optimization tasks. A simple postprocessing greedy algorithm to locally refine pipe replacements is introduced as a means of complementing the evolutionary approach.

A multiobjective approach is used here to optimize design and operation of the C-Town pipe network, searching for trade-off solutions between (1) installation cost, (2) operational cost, and (3) cost of the pressure-reducing valves. Due to the large number of decisional variables and to the complexity of the constraints considered, the optimization problem was tackled in five steps: (1) identification of some feasible (on the basis of the many constraints) first attempt solutions; (2) application of a multiobjective genetic algorithm to the 2D optimization problem with objective functions 1 and 2, in order to obtain optimal trade-off solutions between the installation cost and operational cost, without considering the installation of pressure-reducing valves; (3) application of the multiobjective genetic algorithm to the optimization problem with objective functions 2 and 3 for each of the solution selected at the end of Step 2, in order to assess how the operational cost can decrease thanks to the installation and operation of pressure-reducing valves; (4) derivation of the 3D Pareto surface by grouping the solutions found at the end of Steps (2) and (3). A solution was extracted from the 3D Pareto surface of optimal solutions following some specific criteria. This solution was then further refined (Step 5) in order to allow for variable settings of the pressure-reducing valves installed and to make it compliant with the battle guidelines concerning leakage modeling.

This paper presents a methodological solution to The Battle of Background Leakage Assessment for Water Networks (BBLAWN) competition. The methodology employs two constrained multiple-objective optimization problems and is implemented in the context of a software application for the generic hydraulic optimization and benchmarking of water distribution system (WDS) problems. The objectives are the combined infrastructure and operational costs and system-wide leakage, both to be minimized. In order to accelerate the evaluation of potential solutions, a distributed computing approach permits multiple EPANET solutions to be evaluated in parallel. A pressure-driven demand extension to EPANET assists the optimization in accurately ranking near-feasible solutions and to dynamically allocate leakage demand to nodes. Pressure-reducing valves (PRVs) have been located in two ways: a priori, with respect to the optimization analysis, and a posteriori after the infrastructure optimization to reduce excess pressure and pipe leakage. The latter demonstrates better overall fitness, leading to optimal configurations dominating those obtained with the former. Several temporal resolutions for PRV settings have been evaluated to contrast the optimal solutions with the computational effort required.

Leaks in water distribution systems waste energy and water resources, increase damage to infrastructure, and may allow contamination of potable water. This research develops an evolutionary algorithm-based approach to minimize the cost of water loss, new infrastructure, and operations that reduce background leakage. A new design approach is introduced that minimizes capital and operational costs, including energy and water loss costs. Design decisions identify a combination of infrastructure improvements, including pipe replacement and valve installment, and operation rules for tanks and pumps. Solution approaches are developed to solve both a single-objective and multiobjective problem formulation. A genetic algorithm and a nondominated sorting genetic algorithm are implemented within a high-performance computing platform to select tank sizes, pump placement and operations, placement of pressure-reducing valves, and pipe diameters for replacing pipes. The evolutionary algorithm approaches identify solutions that minimize water loss due to leakage, operational costs, and capital costs, while maintaining pressure at nodes and operational feasibility for tanks and pumps. Solutions are compared to identify a recommended design. The framework is demonstrated to redesign a water distribution system for an illustrative case study, C-Town.

This paper proposes a methodology to decompose water distribution systems (WDSs) into a twin-hierarchy pipeline structure consisting of backbone mains and community feeders. The method has three steps: (1) clustering analysis; (2) vulnerability analysis; and (3) identification of backbone mains and community feeders. After decomposition, analysis of a whole complex WDS could be simplified to that of smaller subsystems formed by either backbone mains or community feeders. The method enables the analysis of all communities independently without physical division of the WDS. It is applied to an optimal-design problem of the C-Town network defined in the literature. The problem is to find the best tradeoff between reducing background leakage and minimizing capital and operational costs. The final solution has a total annual cost of 1.19 million Euro with 54% operational costs and 46% capital costs, respectively. The decomposition process is also consistent with engineering practice on leakage control since one practical strategy is to divide the WDSs into metered zones. Other possible applications of the twin-hierarchy decomposition are further discussed.

This paper summarizes an approach for the assessment and control of background leakage on water distribution networks. The methodology was developed for the battle of background leakage assessment for water networks (BBLAWN) held at the Water Distribution System Analysis Conference 2014 in Bari, Italy. The problem instance posed for the conference considers an aging water network with high levels of background leakage. A range of operational and design changes including new valves, pipes, pumps, tanks, and controls are available to reduce the expenditure needed to operate the system. Constraints are imposed on nodal pressures and tank levels to meet service level requirements. The solution methodology proposed in this paper decomposes the problem according to the type of intervention, considering each type separately. An initial diagnosis of the network informs the manner and order of evaluating the various interventions. Custom implementations of network simulation, heuristic algorithms, and optimization models are used to identify improvements. The recommended program of network modifications reduced the annual cost of running the system from €4 million to €1.5 million and had a return on investment in network infrastructure of 430%.

Sustainability is a major issue for water companies, who have to provide high quality services at achievable costs. In this context, water loss control and energy efficiency are two great challenges water companies have to face. Water loss represents both higher service cost (real losses) and loss of revenue (apparent losses), while the energy bill from treatment plants and pumping stations represents a significant part of the service cost. The Battle of Background Leakage Assessment for Water Networks (BBLAWN) was a competition dedicated to this subject: water distribution network (WDN) optimal management. Teams/individuals from academia, consulting firms, and utilities were invited to propose methodologies for solving the C-Town WDN problem: minimize operational and capital costs and background leakages. This paper presents one of the methodologies proposed at BBLAWN. The methodology proposed here to solve the C-Town WDN problem comprises two optimization models: a least-cost design model to identify the pipes to be replaced and size them, and an optimal operation model to define the pump controls and the PRV settings. Both models are solved by linking a hydraulic simulation model with a simulated annealing algorithm. This approach, supported by some additional engineering expertise, provided a set of good solutions in terms of operational and capital cost, and a good compromise with the environmental and financial damage caused by water losses.

The solution approach proposed in this paper is on the basis of trial-and-error methodology, using heuristic methods with simulation at the battle of background leakage assessment for water networks (BBLAWN). To achieve the optimal solution, customized researched tools were developed for water distribution system (WDS) optimization. These include subroutines for: optimization of water tanks levels to switch pumps on and off; estimation of the influence of the pressure-reducing valves (PRVs) on leakages, to make a decision whether there is a justification for adding a PRV to a pipe or not; calculation of leakages under different conditions; and replacing old pipes with new ones. For design decisions, commercially available tools were also used, carrying out comparison of various network structures (parallel pipe alternatives). The final result included the installation of 80 PRVs, the replacement of 370 pipes, and the change of 2 pump elements; the pumping schedule, on the basis of water tank levels, was also optimized.

This paper presents a methodology for optimizing the operations of water distribution networks. The methodology combines the use of best management practices with a pseudogenetic algorithm, and has been applied to solve the problem of the battle of background leakage assessment for water networks. This problem involves more than 70,000 decision variables. To reduce this number, the problem was divided into three steps. First, a preliminary analysis was performed to define criteria for the replacement of pipes and pumps with a definition of potential subareas. Then, an optimization model was used to determine the pump schedule and pipe replacement. Finally, fine adjustments were performed including pump replacement, control pressure valve usage, and valve-setting definition. The main conclusion derived from this work is that a proper combination of optimization techniques and manual adjustments based on the use of engineering judgment is suitable to solve generic problems in water supply networks.

This paper presents a methodology to rehabilitate and manage leakages on the C-Town water distribution system. A hydraulic model with emitters was considered to represent pipe leakages as concentrated flows in the nodes. The proposed methodology introduces two hydraulic concepts: the unit headloss to rehabilitate the network and the flow-pressure criterion to determine the location of valves; in addition, it uses genetic algorithms for pump optimization processes. This approach aimed to apply a pressure management scheme consisting in the allocation of valves to reduce both energy and leakage costs. The final result shows that all the requirements of the problem were satisfied with little computational effort, as expected, using hydraulic-based processes and criteria, compared to a formal heuristic approach. The introduced concepts allowed constructive and operational cost minimization. In relation to the leakage reduction, the use of emitters did not represent well pipe losses in the sense that pressure reduction strategies were not effective for this particular problem, limiting the leakage cost reduction. However, those strategies have shown good performance in other network analyses.

The design of water distribution networks (WDNs) is a complex nonlinear problem that has been solved using optimization techniques attempting to find near-globally optimal solutions. This paper demonstrates that relying on engineering judgment, with very limited use of optimization, can generate reasonable quality approximations of the Pareto front of multiobjective WDN design problems without intensive computational requirements. First the results of the implementation of a previous implementation of the engineering judgment approach to the Battle of Background Leakage Assessment for Water Networks (BBLAWN) design competition is summarized. Additionally, a simplified version of the BBLAWN problem is solved using both the engineering judgment approach and a multiobjective optimization algorithm and the corresponding Pareto fronts are compared. Relative to other BBLAWN solutions, the engineering judgment solution produced a high-quality result with a very small computational budget and was able to identify a more realistic number of changes in the WDN ($\sim 10\%$ of the network) compared with BBLAWN teams relying on global optimization algorithms.