Simulation of Runoff Pollutant Control Effectiveness of Rain Garden Facilities Based on SWMM

In order to enhance Low Impact Development (LID) technology and promote a green, energy-efficient development concept, we conducted research on the soil composition and the runoff purification effectiveness of rain gardens located in a residential area of Pudong, Shanghai. Using data from monitoring stations and exploratory information, along with the building and drainage master plans, we developed a model of the area's facilities and drainage network in SWWM. Using four pollutants: TSS, TP, TN, and COD. We simulated the reduction effects of four rain garden optimization schemes on surface runoff and pollutants in runoff under four recurrence periods: 0.5, 1, 2, and 5 years. The results indicate that the optimal runoff control effect is achieved in synthetic soil, followed by gravelly sand soil. Compared to the scenario without a rain garden, the average runoff control rate of both types of soil exceeds 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup>, meeting the rain garden control effect requirements for the region. In comparison, loam-organic mixtures and bark mulch show some control effect on stormwater runoff in planting soil design schemes, but the effect is relatively poor. The synthetic soil exhibits a higher reduction rate for suspended solids (SS) and total nitrogen (TN), with a reduction rate of 33%, significantly decreasing the peak concentration and total amount of SS in runoff. The gravelly soil demonstrates the highest efficiency in reducing chemical oxygen demand (COD), achieving a reduction rate of up to 34%. Standard planting soil shows the best retention effect for total phosphorus (TP), with a reduction rate of 21%. Overall, the loamy organic mixture is the most suitable for future construction in the study area.