Mitigating the Effects of Low-Impact Development on Waterlogging and Non-Point Pollution Under Different Confluence Relationships

Intensifying urbanization and climate change have highlighted the growing role of low-impact development (LID) practices in urban rainwater management systems. However, there is still room for improvement to optimally deploy LID practices, especially under different confluence relationships. In this study, 36 scenarios were designed based on different rainfall conditions, LID practices, confluence relationships, and locations, which were analyzed using hybrid hydraulic and water quality modeling. The following key results were obtained: (1) Series II was the main confluence path in the study area. The greenbelt occupied a large share; accordingly, the control of waterlogging and non-point source pollution in series II was better in the designed rainfall scenarios. (2) In the designed rainfall scenarios, series I had the best mitigation effect on waterlogging and non-point source pollution, with 24.5%, 16.4%, and 15.2% lower values than those of the series II and Parallel scenarios. There were no significant differences among the three confluence relationships under extreme rainfall. (3) Among the different LID practices, bioretention cells contributed to the maximum reduction in pollution (29.91%). Green roofs and permeable pavement resulted in the maximum reductions in total runoff (27.99% and 22.94%, respectively), and permeable pavement also reduced pollution by 26.50%. These results suggest that the pavement at some waterlogging points should be replaced with permeable pavement to avoid the negative effects of future extreme rainfall.