Abstract
The optimisation of water distribution networks (WDNs) by evolutionary algorithms has gained much coverage in the literature since it was first proposed in the early 1990s. Despite being well studied, the problem and objectives continue to evolve as demands on water companies change. Motivated by the increased focus on reducing the risk of discolouration, this study examines a three objective version of the WDN design problem which takes into account cost, head excess and discolouration risk. Using this formulation, this paper presents a method for producing optimised network designs aimed at reducing discolouration risk in the network design phase and thus reducing the associated long-term maintenance and operational burdens of the system. This paper discusses the use of a discolouration risk model and, using this model, the optimisation of network design, specifically pipe diameters, to produce a range of high quality self-cleaning networks. The network designs are optimised using the Markov-chain hyper-heuristic (MCHH), a new multi-objective online selective hyper-heuristic. The MCHH is incorporated in to the known NSGA-II and SPEA2 and supplied with a range of heuristics tailored for use on the WDN design problem. The results demonstrate an improvement in performance obtained over the original algorithms.
Highlights
The UK water industry is tightly regulated by Ofwat, the UK regulatory body, with the performance of water companies closely monitored by a range of indicators; from water quality, customer service to customer satisfaction
In this paper we investigate the use of discolouration risk as an objective in a multi-objective algorithm and propose a new hyper-heuristic called the Markov-chain hyper-heuristic (MCHH) for the multi-objective optimisation of water distribution networks (WDNs)
A key aim of this study is to examine the impact of pipe diameters on discolouration risk and demonstrate a method to reduce that risk in parallel with optimising network design and/or rehabilitation cost whilst meeting head requirements in a novel consideration of the WDN design and rehabilitation problems
Summary
The UK water industry is tightly regulated by Ofwat, the UK regulatory body, with the performance of water companies closely monitored by a range of indicators; from water quality, customer service (e.g., sufficient pressure) to customer satisfaction. An emphasis has been placed on customer satisfaction in particular, which is partly measured by monitoring customer complaints and contacts Motivated by these regulatory demands, water companies are focusing efforts on reducing the frequency of water discolouration events (Cook ) prior to customer contacts occurring. Discolouration events (the visible discolouration of water at the tap) have been attributed to approximately 30% of all complaints received by water companies in the UK (Cook ). It should be noted, that the drive to reduce the number of discolouration events is not isolated to the UK, but experienced in many countries, worldwide. The notion of self-cleaning thresholds have been investigated a number of times by Boxall & Prince ( )
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