Reliability Assessment Model for Water Distribution Networks

The aging water distribution networks in the US are approaching the end of their useful life, and more than 240,000 pipeline breaks are estimated to occur every year, which corresponds to an average of 25 breaks (or 100 mi) per year. Due to financial restrictions to maintain and rehabilitate their water distribution networks, many municipalities need to assess the reliability of their network and properly plan for their maintenance. Previous studies have mainly focused on the reliability assessment of individual network components such as pipes. Moreover, very limited network reliability models addressed the importance of network segments with customer accessibility to drinking water. Therefore, a model is developed in this study to evaluate the reliability of water distribution networks taking into consideration the weight of the importance of their segments. A modified Preference Ranking Organization METhod for Enrichment Evaluations (PROMETHEE) technique was applied to obtain the weight of the importance of segments using expert opinions. The working and failing states of pipes and segments were determined by developing the network's failure tree, and their impacts on the network reliability were estimated. The evidential reasoning was applied to aggregate the effects of failure and working states of each component on the whole network and its segments. The failure rate and reliability of each component were determined based on what is available in the literature. Results obtained from PROMETHEE application showed that network segments of health care facilities are first in rank of the highest importance. Hence, maintenance and rehabilitation of these segments shall receive the top priority. A network in a Canadian city, which was evaluated using the proposed model, was found to have a reliability index of 0.93.