Reliability-based strengthening and expansion of water distribution networks

An iterative method based on the trade-off between reliability and cost is proposed for the strengthening and expansion of water distribution networks (WDNs) to obtain a level-one redundant network, i.e., a network that can sustain single pipe failure without affecting the consumer services either in part or in full. Reliability is assessed using the node and volume reliability factors which are evaluated considering the performance of WDNs under different conditions. Reliability of an existing network is improved at every iteration by either adding a parallel pipe of minimum size to one of the existing links, or increasing the size of one of the newly added (strengthened or expanded) pipes to the next higher size by considering the largest ratio of the marginal capacity factor to the marginal increase in cost. The method is initially illustrated with an example of a multisource network having time-varying demands. Then, a network in Washington, D.C. having multiple demand patterns is designed and the results are compared with those obtained by a linear-programming based algorithm.