Segment Based Reliability Assessment for Water Distribution Systems under Multiple Failure States

In recent years, water utilities have placed a greater emphasis on the reliability and resilience of their water distribution networks. This focus has increased due to the continuing aging of such infrastructure and the potential threat of natural or man-made disruptions. As a result, water utilities continue to look for ways to evaluate the resiliency of their systems with a goal of identifying critical elements that need to be reinforced or replaced. Most research in the past has assumed that pipe breaks can be characterized as the loss of a single pipe element. This assumes that each pipe has an isolation valve on both ends of the pipe that can be readily located and operated under emergency conditions. This is seldom the case. The proposed methodology takes into account that multiple pipes may be impacted during a single failure as a result of the necessity to close multiple isolation values in order to isolate the “segment” of pipes necessary to contain the leak. This paper presents a simple graphical metric for use in evaluating the performance of a system in response to a pipe failure using three different performance metrics: percent loss of system demand, percent loss of acceptable pressures, and percent loss of adequate water age. The associated metric is applied to three different water distribution systems in an attempt to illustrate the fact that different pipe segments may impact system performance in different ways. This information is critical for use by system managers in deciding which segments to prioritize for upgrades or replacement.