Influence analysis of different design conditions on urban runoff and nonpoint source pollution

Urban waterlogging and nonpoint source (NPS) pollution caused by urbanization have considerably increased, and their control effects are affected by many factors. This study established a distribution model to analyze the influences of different rainfall conditions and rain garden layouts on runoff output and NPS pollution. Simulation results showed that (a) the reduction rates of the runoff and pollution load decreased from 45% to 23% and from 57% to 23% with increasing rainfall duration (1-24 hr). The flow and concentration peaks, total discharge amount and load increased, and the reduction rates of the runoff and pollution load decreased from 47% to 32% and from 60% to 21%, respectively, with increasing recurrence period (1-50 annual). The changes in the rain peak coefficient had minimal reduction effect on water quantity and quality. (b) Under different rain garden layouts, the reduction rates of the runoff and pollution load were 37%-52% and 13%-57%, respectively. The reduction effects of the runoff and pollution load improved, whereas amplitudes decreased with increasing rain garden layouts (0%-4%). (c) Rainfall duration and rain garden proportion greatly influenced the runoff and load reductions, respectively. PRACTITIONER POINTS: The reduction effects of runoff and pollution load under different rainfall conditions were simulated and analyzed. The reduction effects of runoff and pollution load under different setting proportions of rain garden were simulated and analyzed. The influence degrees of different design conditions on water quantity and quality reduction rates were evaluated.