Effects of rain flood control about low impact development system in West 10 Plot of Shougang based on the SWMM simulation

ObjectiveAccording to the requirements of New Shougang High-End Industry Comprehensive Service Area Control Detailed Planning, West 10 Project carries out rainwater system with the goal of eliminating Beijing's 3-year return period of 24 hours rainfall (108 mm). This study corresponds rainwater system design strategy according to the current characteristics, which concludes rainwater infiltration-retention system and storage-utilization system.

MethodFor the infiltration-retention system, two development models of low impact development and traditional development were established through SWMM, simulating rainwater runoff discharge under 24 hours rainfall in different return periods (1, 2, 3, 5, 10 and 20 years) to analyze the regulative effect of two development models in total runoff, peak flow as well as time of peak flow appearance. For the storage-utilization system, simulating the annual rainfall process in 2017 through SWMM and counting the total amount of rainwater collected by the rain retention barrel on a weekly basis, which was compared with the irrigation water demand of the West 10 Plot was to analyze the utilization of rainwater collected in the rain retention barrel.

Result(1) According to the current situation of the site, West 10 Plot had been designed six LID facilities, which was green roof, permeable pavement, rain garden, vegetative swale, bio-retention cell and rain retention barrel. In the return periods from 1 to 20 years, the reduction rate of the runoff volume of the low-impact development system in West 10 Plot was 100%, 100%, 100%, 78.79%, 50.41%, 34.73%, and the reduction rate of the peak flow was 100%, 100%, 100%, 70.12%, 33.33%, 19.44%. The peak value disappeared in the 1-3 year return periods, and the time of peak flow appearance was delayed by 375, 310 and 240 min. (2) The rain retention barrel of exogenous rainwater area stored 9 617 m³ rainfall for the whole year of 2017. The rainwater collection was mainly concentrated in the 25th to 35th week. The maximum water collection per week was 2 078 m³, which occurred in the 27th week (at the beginning of June), the water collection in the first to 20th week and the 43th to 52nd week was basically zero. In week 25, 27, 29-32, 34-35 and 41 of 2017, the amount of water collected in the rain retention barrels was still sufficient after meeting the irrigation demand of the West 10 Plot, and the vacancy rate of the rainwater storage barrels in winter was relatively high.

Conclusion(1) LID facilities had a good control effect on rain-flood problems, which can reduce the total runoff, peak flow and delay the peak time. However, with the delay of time, the capacity of LID was gradually weakened, so it can be seen that the rain-flood control capacity of low-impact development systems had an upper limit. (2)According to the statistics of the annual rainfall daily value of 2017 in Beijing, the utilization rate of runoff collection in the rain retention barrel of the exogenous rainwater area was 43.65%, and the vacancy rate of the rain retention barrel in 30 weeks (210 days) was 100%, which was relatively wasteful. Therefore, the cost and other factors should be taken into account in the low-impact development system design.