Guan'gai paishui xuebao (Aug 2022)
The Effect of Bioretention Systems on Stormwater Runoff of Shijiazhuang
Abstract
【Objective】 Bioretention is a method to purify water, and the aim of this paper is to study its effect on stormwater runoff. 【Method】 We took stormwater runoff in Shijiazhuang city as an example, investigating the outflow characteristics of the bioretention system in response to two rainfall patterns, constant pattern and Chicago pattern using column experiment and HYDRUS model. From the simulated results, we analyzed and discussed the sensitivities of the runoff to soil hydraulic parameters, catchment area and thickness of the planting soil layer. We also developed a model to predict the influence of rainfalls with different return periods (N) on outflow. 【Result】 Compared to constant rainfall, the Chicago rainfall pattern delayed the emergence of outlet-outflow and prolonged the ponding duration on the soil surface. The hydraulic parameters to which the runoff was sensitive include saturated soil permeability Ks, saturated soil water content θs, and the empirical parameter α in the van Genuchten formula. An increase in Ks increased the maximum outlet-drainage rate and brought forward its arrival time. Increasing θs prolonged the latent time and reduced the outflow rate and ponding duration. Increasing the parameter α resulted in an increase in outflow. Doubling the catchment area ratio increased the maximum drainage rate, the peak-reduction rate and ponding duration by 13%, 33% and 300%, respectively, whereas reducing the latent time by 16%. Change in thickness of the planting soil layer did not show a significant effect on the outflow pattern. 【Conclusion】 The bioretention system is more permeable with more than 90% of rainwater flowing through the planting soil layer. When the return period of the rainfall is no more than 5 years, there is no overflow with the peak reduction rate being 40.6%~76.5%, the latent time > 1 h and ponding time < 2 h.
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