Transient-Aware Multi-Objective Optimization Framework for Water Distribution Systems: Balancing Cost and Fire Flow Reliability

This paper proposes a multi-objective optimization framework that integrates fire flow failure probability analysis and hydraulic transient considerations into a least-cost design methodology. The framework combines (1) an analytical probabilistic model for estimating fire flow failure probability and (2) a transient model of evaluating fire flow conditions, both incorporated into a non-dominated sorting genetic algorithm. Pareto-optimal solutions are constrained to ensure transient pressure heads remain below permissible limits. The trade-off between capital cost and fire flow reliability is achieved through optimized pipe diameter selection and pump configuration. Case studies demonstrate that a minimum 150 mm distribution main—a common industry standard—not only enhances fire flow capacity but also effectively mitigates transient pressures. The results highlight that transient severity is a critical driver of both economic design and system performance reliability.