A methodology is being developed that may be incorporated in a hydraulic network modelling tool to analyse redundancy in the trunk main network of a water distribution system. A rigorous definition of the terms redundancy and security are given in this paper. Redundancy in the trunk main infrastructure is assessed in terms of supply security, which is the probability of water of adequate pressure, quality and appearance reaching the demand nodes. Supply security is increased by providing multiple supply routes to demand nodes so that there is minimal supply interruption in the case of failure of a network component.
This paper presents a method that evaluates supply security under network conditions caused by trunk main failures. The supply security level ensured by multiple pipe routes is compared with the costs of maintaining additional routes. Three indices are used as measures of the cost of additional infrastructure: network condition, water age and link failure probability. The fitness of a trunk main system is evaluated in terms of supply security and infrastructure costs. The system may then be modified using a genetic algorithm to create a population of reduced networks, from which infrastructure which may be redundant has been removed. The fitness of each reduced network is assessed, compared with the fittest network, and progressive generations are developed using the algorithm, until an improved network is selected.