Modelling water distribution systems with deficient pressure

The pressure dependency of withdrawals from water distribution systems under conditions of abnormal stress, such as mains failure or fire fighting, is well accepted. A simple sequential solution seeking iterative approach to obtain a solution for pressure constrained outflows (including leakage) based on repetitive substitution into conventional computational algorithms, where demands are generally predetermined, has been developed. The methods are presently configured to use the computational efficiency and versatility of the widely used EPANET-2 software routine, offering the benefits of full network operational specifications at the level of ‘commercial’ network applications. Application of the new algorithm to UK water networks under various partial failure conditions has given insight into the ‘true’ extent and scale of supply deficiency as a consequence of pressure shortfall. The failures of one link of the network at a time have been simulated. The results suggest that, in terms of the nodes (properties) affected by shortfall in pressure, the more rigorous approach reduces the zone of deficient service compared with that flagged by conventional investigations. A case study used the methodology to investigate loss of resilience arising from pressure management and to assess the susceptibility to supply interruption of sensitive customers.