An SWMM-Based Approach to Urban Stormwater Drainage Network Optimization

Abstract

This study is motivated by the increasing need to mitigate storm-induced urban flooding, particularly in highly developed environments near floodplains or humid coastal regions, where climate change has intensified extreme rainfall events. The study explores a top-down approach to stormwater drainage system design, contrasting with the conventional bottom-up implementation commonly seen in urban planning.Two drainage pipe network layouts are evaluated within the Storm Water Management Model (SWMM) under identical storm conditions: one with a 4:1 inlet-to-outlet ratio per junction (shorter total flow path) and another with a 2:1 inlet-to-outlet ratio per junction (longer flow path with intermediate layer of pipes). Performance is compared based on runoff-outflow delay and internal system storage volume, using a controlled study area with consistent input parameters. To improve simulation accuracy, additional pipe flow networks replicating overland flow paths are incorporated, ensuring the full water movement process is represented—from surface accumulation to final discharge. Findings indicate that reducing in-system flow path length minimally impacts outflow delay, whereas shortening overland flow paths by increasing drainage inlets significantly improves performance. Results also suggest that dynamic storage volume does not correlate with discharge flow rate, indicating potential for increasing internal storage through intermediate pipe layers and extended conduit paths without negatively affecting system efficiency.