This paper describes a penalty-free multi-objective evolutionary optimization approach for the phased whole-life design and rehabilitation of water distribution systems. The optimization model considers the initial construction, rehabilitation and upgrading costs. Repairs and pipe failure costs are included. The model also takes into consideration the deterioration over time of both the structural integrity and hydraulic capacity of every pipe. The fitness of each solution is determined from the trade-off between its lifetime costs and its actual hydraulic properties. The hydraulic analysis approach used, known as pressure-dependent modelling, considers explicitly the pressure dependency of the water supply consumers receive. Results for two sample networks in the literature are included that show the algorithm is stable and finds optimal and near-optimal solutions reliably and efficiently. The results also suggest that the evolutionary sampling efficiency is very high. In other words, the number of solutions evolved and analysed on average before finding a near-optimal solution is small in comparison to the total number of feasible and infeasible solutions. We found better solutions than those reported previously in the literature for the two networks considered. For the Kadu network, for example, the new best solution costs Rs125,460,980-a significant improvement. Additional statistics that are based on extensive testing are included.

This paper describes the development and application of a new multiobjective evolutionary optimization approach for the design and upgrading of water distribution systems with multiple pumps and service reservoirs. The optimization model employs a pressure-driven analysis simulator that accounts for the minimum node pressure constraints and conservation of mass and energy. Pump scheduling, tank siting and tank design are integrated seamlessly in the optimization without introducing additional heuristic procedures. The computational solution of the optimization problem is entirely penalty-free, thanks to pressure-driven analysis and the inclusion of explicit criteria for tank depletion and replenishment. The model was applied to the Anytown network that is a benchmark optimization problem. Many new solutions were achieved that are cheaper and offer superior performance compared to previous solutions in the literature. Detailed and extensive simulations of the solutions achieved were carried out. Spatial and temporal variations in water quality were investigated by simulating the chlorine residual and disinfection by-products in addition to water age. The hydraulic requirements were satisfied; efficiency of pumps was consistently high; effective operation of the new and existing tanks was achieved; water quality was improved; and overall computational efficiency was high. The formulation is entirely generic.Keywords Demand-driven analysis . Pressure-driven analysis . Penalty-free constrained multiobjective evolutionary optimization . Water distribution system . Optimal pump scheduling . Service reservoir design and operation Water Resour Manage (2016) 30:3671-3688

Simulation models for water distribution networks are used routinely for many purposes. Some examples are planning, design, monitoring and control. However, under conditions of low pressure, the conventional models that employ demand-driven analysis often provide misleading results. On the other hand, almost all the models that employ pressure-driven analysis do not perform dynamic and/or water quality simulations seamlessly. Typically, they exclude key elements such as pumps, control devices and tanks. EPANET-PDX is a pressure-driven extension of the EPANET 2 simulation model that preserved the capabilities of EPANET 2 including water quality modelling. However, it cannot simulate multiple chemical substances at once. The single-species approach to water quality modelling is inefficient and somewhat unrealistic. The reason is that different chemical substances may co-exist in water distribution networks. This article proposes a fully integrated network analysis model (EPANET-PMX) (pressure-dependent multi-species extension) that addresses these weaknesses. The model performs both steady state and dynamic simulations. It is applicable to any network with various combinations of chemical reactions and reaction kinetics. Examples that demonstrate its effectiveness are included.

Water quality models are increasingly being routinely used to help ascertain the quality of water in drinking water distribution systems for design and operational management purposes. Conventional water quality models are demand driven and consequently do not incorporate the effects of any deficiency in pressure on the water quality throughout the distribution network. This paper assesses a new integrated pressure-dependent hydraulic and water quality model. The model is an extension of the well-known Epanet 2 model that has an embedded logistic pressuredependent nodal flow function. Hydraulic and water quality analyses based on two water supply zones in the UK were conducted for a range of simulated operating conditions including normal and subnormal pressure and pipe closures. It is shown that operating conditions with subnormal pressures, if severe and protracted, can lead to spatial and temporal distributions of the water age and concentrations of chlorine and disinfection by-products that are significantly different from operating conditions in which the pressure is satisfactory. The results presented may be indicative of modelling errors that may not have been recognised explicitly hitherto.

The need for accurately predicting water quality through models has increasingly been crucial in meeting rigorous standards and customer expectations. There are several endeavours on developing robust water quality models for water distribution systems. In this paper, two variants of the EPANET 2 water quality model have been assessed to inform future research. The models are the multiple species extension EPANET-MSX and the pressure-dependent extension EPANET-PDX. Water quality analysis was conducted on a hypothetical network considering various operating pressure conditions. Different kinetic models were employed to simulate water quality. First order, limited first order and zero order models were used for predicting chlorine residual, disinfection by-products (DBPs) and water age respectively. Generally, EPANET-MSX and EPANET-PDX provided identical water quality results for normal operating conditions with adequate pressure but different results for pressure-deficient networks. Also, a parallel first order model with fast and slow reacting components was used for chlorine decay and DBPs using the EPANET-MSX model for a network operating under normal pressure conditions.