Risk assessment of water supply interruptions due to mechanical pipe failures

The mechanical pipe failures (i.e. pipe bursts) in Water Distribution Systems (WDS) typically cause severe interruptions in supply to the nearby properties and a partial reduction in supply to the customers living in a wider area (usually as a consequence of a reduced system pressure in the area). A procedure for the quantitative risk assessment of water supply under such conditions is presented here. The risk is defined as the product of the probability of failure (i.e. pipe burst(s)) and the consequence of that failure (quantity of water not delivered). The risk assessment procedure uses the recently developed pressure head-driven hydraulic model used to perform Extended Period Simulation (EPS). The new model is capable of automatic detection of topological network changes due to pipe(s) mechanical failures. The model is run iteratively to integrate the supply interruption risk under a number of different pipe failure scenarios. The relevant risk measures are defined at two levels (network node and whole system) to capture different spatial scales of the problem. The procedure is tested and verified on a real-life case study involving the water distribution system of Apulia (Italy). It is envisaged that the risk assessment procedure developed and presented here can be effectively used as a part of a decision support system for planning maintenance and/or rehabilitation activities of a water distribution system.