Variance of pipe flow-series as surrogate reliability measures in design of water distribution networks

Water distribution systems (WDSs) are designed to provide consumers adequate quantity of water with sufficient pressure and of acceptable quality at all the times under a range of operating conditions. How best a network satisfies to achieve this objective is termed as its reliability. Reliability is classified into different types as described in previous studies such as mechanical reliability, hydraulic reliability and water quality reliability. Hydraulic reliability refers to network tolerance for demand changes. Mechanical reliability refers to how well WDS can perform under abnormal situations such as pipe bursts and pump failure conditions. Water quality reliability measures refer to quality of water delivered to consumers under any mechanical or hydraulic uncertainty over time. Reliability based design of water distribution network is an active area of research and is a challenging task as it requires complex sampling and iteration procedures. Focussing on this aspect, recently various reliability surrogate measures are introduced by different researchers for hydraulic reliability and mechanical reliability of WDS. These surrogate measures mainly aims at simplifying the reliability considerations in design. The improvement in surrogate measures shows improvement in performance of network under failure and uncertain conditions.