Reliability‐Constrained Pipe Network Model

Abstract

A new methodology for incorporating reliability considerations directly into least‐cost optimization design models for looped water distribution networks is presented. The essence of the methodology is the measurement of reliability and making changes to the distribution system if the reliability is found to be unsatisfactory. The optimization model constrains the probability of pipe failure for each link and the probability of demand exceeding design values at each node for a fixed flow pattern in the network. The probabilities of pipe failure and demand exceedance are combined into a single reliability measure, the probability of no node failure. Due to the relationship between changing pipe breakage rates and pipe capacity, changing the demand exceedance probability also tends to reduce the probability of pipe failure. On the basis of earlier work, a simple reduction in the probability of the node demand exceeding the design values, through increasing the severity of the design flow, is used to achieve improvement in the probability of no node failure. Use of the reliability measure and the network reliability improvement procedure is demonstrated by application to a sample network.