Probabilistic Model for Water Distribution Reliability

Abstract

A two-stage methodology for assessment of reliability of water distribution networks recognizing uncertainties in nodal demands, pipe capacity, reservoir/tank levels, and availability of system components is proposed. In the first stage, the probability distribution functions for nodal heads are derived from a linearized hydraulic model on the basis of known probability distribution functions of the nodal demands, pipe roughnesses, and reservoir/tank levels. The effects of nonlinearity in the network hydraulic model are accounted for in this step by partitioning the nodal demands into a number of categories or intervals. The probability of supply failure calculated in this first stage assumes that the system state or configuration is fixed, e.g., certain pipes and pumps are specified as being out of operation; that the pipe capacity varies randomly; and that demands vary around a specified level. The second step involves combining this probability with the probabilities of different system configurations and demand levels to generate the overall reliability measured for the whole system or a particular area of the system.