Carla Tricarico

Battle of the Water Networks II

The Battle of the Water Networks II (BWN-II) is the latest of a series of competitions related to the design and operation of water distribution systems (WDSs) undertaken within the Water Distribution Systems Analysis (WDSA) Symposium series. The BWN-II problem specification involved a broadly defined design and operation problem for an existing network that has to be upgraded for increased future demands, and the addition of a new development area. The design decisions involved addition of new and parallel pipes, storage, operational controls for pumps and valves, and sizing of backup power supply. Design criteria involved hydraulic, water quality, reliability, and environmental performance measures. Fourteen teams participated in the Battle and presented their results at the 14th Water Distribution Systems Analysis conference in Adelaide, Australia, September 2012. This paper summarizes the approaches used by the participants and the results they obtained. Given the complexity of the BWN-II problem and the innovative methods required to deal with the multiobjective, high dimensional and computationally demanding nature of the problem, this paper represents a snap-shot of state of the art methods for the design and operation of water distribution systems. A general finding of this paper is that there is benefit in using a combination of heuristic engineering experience and sophisticated optimization algorithms when tackling complex real-world water distribution system design problems

Economic level of reliability for the rehabilitation of hydraulic networks

The problem of water distribution system rehabilitation is formulated here as a multiobjective optimisation problem under uncertainty. The two objectives are to minimise the structural rehabilitation cost and to maximise the hydraulic reliability of the system. In this context, reliability is defined as a probability of simultaneously satisfying minimum pressure head constraints at all nodes in the network. An economic analysis has been performed, taking into account not only the structural costs but also lost revenue owing to the volume of water required by users but not supplied to them because of the structural inadequacy of the network. Because of the uncertainty in water demand, a probabilistic approach is used within the optimisation model. The probabilistic distribution and its parameters were estimated through an experimental study conducted on a real water distribution network. The recently developed robust Non-dominated Sorting Genetic Algorithm II optimisation algorithm is used to solve the optimisation problem. The methodology presented allows the identification of the specific optimal solution of the Pareto front that corresponds to minimal structural cost and minimal lost revenue yet corresponding to a high level of reliability – the economic level of reliability. This value could be assumed as the optimal solution or as a lower threshold, which restricts the gamut of technically feasible solutions that could be adopted in a rehabilitation programme.

Novel Approach for Side Weirs in Supercritical Flow

AbstractSide weirs are hydraulic structures widely used in practice and extensively studied in the technical literature. The flow along a side weir is a classic example of spatially varied flow, the study of which is generally performed by means of a momentum or energy approach. The momentum approach is usually more accurate but requires the experimental estimation of correction coefficients leading to a formulation that is difficult to apply to a practical design. The energy approach, instead, is not as accurate when the flow depths on the side weir are significantly higher than the same weir crest. A novel, simplified theoretical model for the study of single side weir in a circular pipe, operating in supercritical flow, is proposed. The model originates from an experimental analysis of the flow power variation along the side weir. The proposed model has shown good performance in free surface representation and is capable of estimating the lateral outflow with good accuracy. The suggested formulation is...

WATER DEMAND MODELS FOR A SMALL NUMBER OF USERS

A better knowledge of the residential water consumption and the maximum water requirement allows for a more effective design or management of a Water Distribution System (WDS). The analysis of the behaviour of a small number of users in the request of water might be important also to understand the flow demand of numerous clusters of users supplied by a WDS. Indeed, each flow demand node can be seen as the aggregation of several consumers and, consequently, it represents the sum of several water requirements. An empirical study has been developed by monitoring a WDS in a small town, in southern Italy of about 1,200 inhabitants, in order to investigate water demand patterns and which probabilistic model could be better suitable to represent the residential water consumption. In particular, analysis on the experimental data collected from the system under consideration, has allowed to define probabilistic models which characterise the daily residential water demand. This study has highlighted that the goodness of those models depends on the number of users supplied and on the probability that a tap is opened. By means of statistical inferences on a large data sample, it has been shown that — at least for the range of users herein investigated — the Gumbel and Log-Normal distributions best represent the peak water demand; the mean water demand can be considered Normally distributed; the night flow requirement is well characterised with the Poisson model. In addition, in relation to the number of users supplied, the parameters of the probabilistic models have been estimated. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).

RESIDENTIAL WATER DEMAND - DAILY TRENDS

The behavior of residential users in the request of water influences the demand patterns which characterize the water consumption at each node of the network during the time. This stochastic variable influences greatly the performance of hydraulic networks and a better understanding of residential water consumption variability might allow for a more effective design or management of Water Distribution Systems. In order to contribute to this analysis, stochastic models are herein defined and proposed for representing demand variation, especially at the peak condition. This study is based on an experimental approach, comparing empirical data collected in several real water distribution networks which refer to different habits and number of users. Statistical inferences on large data samples have allowed defining probabilistic models and relative parameters which characterize the maximum water consumption at network nodes. The study has been developed considering both the deterministic cyclical component of the demand variability and its uncertain component that accommodates the random nature of the water requirement. Results obtained have shown that Gumbel and Log-Normal distributions best represent the peak water demand for all the monitoring systems considered.

Hybrid Evolutionary Optimization/Heuristic Technique for Water System Expansion and Operation

AbstractThis 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 press...

MULTIOBJECTIVE OPTIMAL REHABILITATION OF HYDRAULIC NETWORKS BASED ON THE COST OF RELIABILITY

The problem of Water Distribution System (WDS) rehabilitation is formulated here as a multiobjective optimisation problem under uncertain demands. The objectives are to minimise the total rehabilitation cost and to maximise the hydraulic reliability of the WDS. In this context, reliability is defined as a probability of simultaneously satisfying the minimum pressure head constraints at all nodes in the network. The total rehabilitation cost takes into account, not just the structural costs, but also the revenue lost due to the volume of water required by users but not supplied to them because of the structural inadequacy of the network. On this basis, safeguarding the hydraulic reliability of a WDS also implies a reasonable rate of return on the water company’s capital investment. A probabilistic approach is used to characterise demand uncertainties within the optimisation model. The relevant probability density functions and their parameters are estimated through an experimental study conducted on a real-life WDS. The rNSGAII optimisation algorithm is used to solve the optimisation problem. The lost revenue estimation is first performed as a part of the post-optimisation procedure, and then as an integral part of the optimisation process. The results obtained in the two approaches are compared showing the better performance of the integrated type approach. The methodology presented allows the identification of the specific optimal solution of the Pareto front that corresponds to the minimal total rehabilitation cost (structural cost plus lost revenue) yet corresponding to an high level of reliability, – the Economic Level of Reliability (ELR). This value could be assumed as the optimal solution or, allowing for socio-economic considerations (if higher WDS performance standards are required), as a lower threshold of reliability which restricts the range of technically feasible solutions that could be adopted in a rehabilitation programme. This way, the proposed methodology contributes to the definition of the reliability threshold values with which studying or designing a WDS.