A new analytical stormwater model for bioretention systems considering both infiltration and saturation excess runoff generation processes

Bioretention systems are increasingly used as a typical stormwater management measure due to their flexibility of scale and general aesthetic appeal. The main purpose of bioretention systems is to control runoff and their runoff reduction efficiency is affected by parameters such as contributing catchment area, fillings and sizes. Conventional analytical probabilistic studies on bioretention systems only considered saturation excess runoff for simplicity and may cause inaccuracy of estimating runoff. In this study, an analytical stochastic model (ASM) for bioretention systems considering both infiltration-excess and saturation-excess runoff generation processes was derived. The proposed ASM model was validated in a large number of case studies in Guangzhou, Jinan, and Lanzhou, China. Various climate, soil, dimension and land use conditions were investigated and compared. Close agreement was observed between the results obtained from the ASM model and continuous simulation results. The ASM model can be used to conveniently evaluate the runoff reduction efficiency of bioretention systems under different configurations of design parameters. It thus provides a computationally efficient analytical tool for the rapid design, analysis and evaluation of the nature-based solution to sustainable urban stormwater management.