assessment, bioretention facilities, minimum inter-event time, swmm, volume capture ratio of annual rainfall, Environmental technology. Sanitary engineering, TD1-1066

Volume capture ratio of annual rainfall (VCRAR) is the key parameter of low-impact development (LID) facilities design, which is significantly affected by the rainfall event division method. However, there is no universal agreement on how to determine an optimal division method to achieve it. A modified minimum inter-event time (MIT) method based on MATLAB software was proposed to find an optimal MIT value. The result showed that the optimal MIT value in Beijing is 200 min based on the daily rainfall data from 1987 to 2016, and the annual average rainfall events were 34.2 with an average rainfall depth of 13.7 mm. Taking bioretention facilities as an example, the errors of design VCRAR under different MIT values were compared based on a Stormwater Management Model (SWMM). The results showed that when design VCRAR was ≤50, 55–60, 60–75, 75–80 and >80%, the optimal MIT value for LID facilities design was 60, 120, 200, 360 and 1,440 min, respectively. Therefore, the optimal MIT should be flexibly selected with the changing of design VCRAR, to ensure that LID facilities meet the design goals. HIGHLIGHTS Combining the MIT with threshold statistical methods based on MATLAB software to obtain an optimal MIT value.; Comparing the effect of different MIT values on the design VCRAR based on SWMM.; RER, ERD and MERDR were analyzed under different MIT values.; The different optimal MIT values of different design VCRARs were obtained in Beijing.;