A New Reliability Index for Evaluating the Performance of Water Distribution Network

Various reliability indices have been defined by researchers for the water distribution networks. Due to the complexity and heterogeneous nature of distribution networks, results of indicies can vary substantially and municipalities have hard time to select the most practical indicies for their networks. This study was undertaken to develop a new method for identifying the best reliability index by considering various factors including the appropriate sensitivity to changes in network parameters, the appropriate shift in extreme conditions, the capability in covering critical condition, hydraulic condition, and water quality reliability. To accomplish the objective of the study, several water distribution networks were evaluated under multiple scenarios and the optimum reliability indices were verified with an example real water distribution network in Ahar. Controlling parameters included in scenario analysis for network reliability indices include: minimum, maximum and optimal pressure, residual chlorine in nodes, velocity in pipes, nodal pressure reliability, pipe velocity reliability, and nodal residual chlorine reliability . To evaluate the performance of defined index, a two-loop test (critical) were compared with the conventional single-lop test (normal). The performance assessment of indices obtained from this study showed that the index values ranged between 0.11 and 1.0, which indicate the normality and the appropriate sensitivity of the indices. Also, by increasing the residual chlorine of the reservoir, the network reliability index changed from 0.54 to 0.75 and then as the residual chlorine decreases in the distributon network the reliability index decreased back to 0.54. This appropriate shift in reliability index while changing residual chlorine in the network, cearly shows the the effectiveness of new method in determining the reliability indicies under extreme conditions. Also, the new method did not respond to the failure of some network components, as were evident with insignificant change in the indices values under critical conditions. From the results of this study generally can be concluded that the newly defined relability indices is an efficient way for evaluating the performance of water distribution networks.