Optimising Permeable Infrastructure Networks in Sponge City Design for Urban Flood Resilience Using Coupled Hydrological, Clogging and Lifecycle Modelling

Abstract Urban pluvial flooding is intensifying as impervious surfaces expand and extreme rainfall events become more frequent. Sponge city design (SCD) relies on decentralised retention and infiltration, yet planners still lack tools that (i) link the progressive, sediment-driven loss of permeability to maintenance actions, (ii) allocate permeable infrastructure across heterogeneous catchments and (iii) weigh flood-damage savings against lifecycle maintenance costs. This study couples the Storm Water Management Model (SWMM) with a Green–Ampt infiltration scheme modified by an exponential sediment-clogging factor and a lifecycle cost–benefit module. Four scenarios were tested on a synthetic 4.5 km² high-density urban catchment under a 50-year, 24-hour design storm: a pipe-only baseline, 30% permeable interlocking concrete pavers (PICP), 50% permeable infrastructure with bioretention, and an optimised network with subsurface detention and controlled underdrains. The model was calibrated against observed flow data (NSE = 0.88, PBIAS = + 4.2%, RSR = 0.32). The optimised network reduced peak runoff by 43.7% (from 42.6 to 24.0 m³ s⁻¹), reduced total runoff volume by 49.1% and delayed the runoff peak by 68 min. Without maintenance, PICP conductivity fell by 72% within three years, whereas twice-yearly vacuum sweeping sustained about 88% of the initial conductivity. Capital expenditure exceeded that of a conventional upgrade (US$18.4 million versus US$15.5 million), but the discounted payback period was 7.2 years and the 30-year benefit–cost ratio was 2.41; the dominant sensitivities were the flood-damage benefit and the discount rate. The results provide design, maintenance and fiscal guidance for municipal planners moving from reactive to proactive, sponge-city-based drainage planning.