Fractal theory based simplification of complex urban stormwater pipe networks for efficient hydraulic simulation

Study region This study was conducted in Sandringham, Victoria, Australia, including the Melbourne Bay suburbs of Beaumaris, Black Rock, and Sandringham, as well as parts of Cheltenham, Hampton, Highett, and Mentone. This area is a fully residential catchment of about 750 ha, drained by a 46.8 km stormwater pipe network comprising 1480 conduits, 1478 nodes, and five independent outfalls. Study focus The structural complexity of urban drainage networks makes it difficult to balance simulation accuracy and computational efficiency. This study proposes a fractal-based simplification framework for urban stormwater drainage networks to reduce model complexity while preserving the dominant hydraulic response. The framework was applied to the Sandringham stormwater network to evaluate staged reduction criteria and the hydraulic fidelity of the simplified models to the detailed SWMM numerical baseline. New hydrological insights At the intermediate reduction level, simulation time decreased by 52.5%–57.6%, while the maximum absolute errors in outlet peak flow and total outflow volume across six rainfall scenarios were 5.28% and 8.55%, respectively. More aggressive simplification produced non-monotonic responses and larger local discrepancies. These results indicate that fractal characteristics can support structurally interpretable network reduction, but applicability requires evaluation using multiple hydraulic indicators. Without field observations, the comparisons demonstrate agreement with the SWMM baseline rather than predictive accuracy. The framework may support repeated scenario assessment subject to hydraulic-performance constraints.