Optimal Reliability-Based Design of Bulk Water Supply Systems

The hydraulic reliability of bulk water-supply systems can be defined in terms of the failure frequency of the municipal storage tanks they supply: the system fails when the tank runs dry and is functional otherwise. Municipal storage tanks are normally sized according to deterministic guidelines that make allowances for balancing, fire and emergency storage. In this study, genetic algorithm (GA) optimization was used together with stochastic analyses to find the optimal combination of feeder pipe configuration, feeder pipe capacity and tank capacity for a given risk of failure. A sensitivity analysis was conducted to determine the factors that have the greatest impact on the optimal design for an example system. The results showed that the optimal pipe configuration is a single feeder pipe in most cases, but that two parallel pipes are preferable for shorter feeder pipes. It was found that it is often cost-effective to trade off a smaller tank size for a greater feeder pipe capacity. Based on this finding, design guidelines are likely to specify suboptimal solutions in many cases.