Enhancing urban stormwater resilience through lot-scale outlet strategies

Urban lot-scale drainage design plays a crucial role in mitigating surface runoff and enhancing stormwater resilience in residential areas. This study investigated the hydrological responses of three outlet configurations—direct, garden, and bioretention cell (BRC) modes—under varying pervious-area ratios (αPA). A conceptual lot-scale model was developed using the Storm Water Management Model (SWMM) to simulate rainfall–runoff processes for five representative residential lots. Model performance was evaluated in terms of runoff volume reduction, peak discharge reduction, and flow delay. One-way ANOVA and Bonferroni post-hoc tests were applied to assess the statistical significance of outlet configurations and antecedent moisture conditions (AMCs), while a sensitivity analysis was conducted on the saturated hydraulic conductivity (Ksat) of BRC media. The results show that outlet configuration significantly influences lot-scale hydrologic performance. The BRC mode consistently achieved the greatest reductions in runoff volume and peak discharge, followed by the garden and direct modes. Statistical tests confirmed that outlet configuration effects were significant (p < 0.05), whereas AMCs exerted minimal influence. Sensitivity analysis indicated that performance was stable across a realistic Ksat range (100–300 mm/hr), confirming model robustness. Notably, runoff mitigation benefits became more evident when the pervious-area ratio exceeded approximately 25 %–35 %, suggesting a practical design threshold. Although the analysis was limited to a single 2-year design storm without field calibration, the findings provide comparative insights for optimizing lot-scale drainage design. Overall, the study highlights the potential of decentralized outlet strategies—particularly BRC systems—to enhance urban flood resilience and support sustainable stormwater management.