Optimal Layout and Pipe Sizing of Urban Drainage Networks to Improve Robustness and Rapidity

It has been recently observed that traditional probability-based design of urban drainage systems often fails because of frequent heavy rainfall events due to global climate change. Therefore, it is critical to consider a system's ability to prepare, react, and recover from a failure (i.e., resilience) in urban drainage network design. This study proposes a resilience-constrained optimal design model of urban drainage networks that minimizes total system cost while satisfying predefined levels of failure depth and duration. Failure (e.g., flooding) depth refers to the level of system performance degradation, whereas failure duration is the time taken for a system's recovery to its normal state. Optimal layout and pipe sizes are identified by the proposed model comprising the harmony search algorithm for optimization and the storm water management model (SWMM) for dynamic hydrology-hydraulic simulations. The proposed model is demonstrated through the design of two grid networks and an A-city drainage network. The obtained resilience-based design is compared to the least-cost design obtained with no resilience consideration according to optimized layout and pipe sizes and the resulting topological characteristics.