Hydrological performance and design of bioretention systems for heavy rainfall management: A laboratory study

• A laboratory rainfall simulator was developed to test full-scale bioretention cells under heavy rainfall. • Standard bioretention designs (5% area coverage, 100–300 mm/hr conductivity) were ineffective for peak runoff control. • Increasing area coverage to 10–30% improved peak discharge reduction (up to 50%) and delay (up to 82 min). • SWMM model calibration showed strong agreement with observed data (r > 0.9; NSE > 0.8), with noted underdrain flow limitations. • Empirical design equations were proposed for estimating detention time, volume, and peak flow parameters. Bioretention systems are widely used for urban stormwater management, yet their performance under intense rainfall—especially in tropical regions—remains underexplored. This study evaluated the hydrological performance of three full-scale bioretention cells (100 × 50 × 70 cm) with varying soil–sand compositions, tested using a custom rainfall simulator. Saturated hydraulic conductivities ranged from 63.3 to 325.6 mm/hr. The Storm Water Management Model (SWMM) was used to simulate the bioretention cells and was calibrated and validated against experimental data, showing strong agreement ( r > 0.9; NSE > 0.8). Results indicated that standard designs (100–300 mm/hr conductivity; 5% area coverage) were insufficient for mitigating peak flows under heavy rainfall events ( P > 100 mm; i ave > 10 mm/hr). Increasing area coverage from 5% to 30% reduced peak discharge by up to 50%, delayed peak runoff by 82 min, and extended detention time. Runoff volume reductions ranged from 2.1–11.2% for 2-year design storms and 1.4–6.8% for 50-year events. An area coverage of 10–20% is recommended for effective mitigation. Dimensionless empirical equations were developed for design applications, and refinements to SWMM’s percolation modeling are suggested to improve model accuracy.