Study on bioretention for stormwater management in cold climate, Part I: Hydraulics

Hydrologic and water quality modelling of bioretention columns in cold regions

“…The storm events were conducted weekly to bring bioretention columns back to air dry state. And target contaminants were added (as shown in Appendix Table A1) into the stormwater to imitate pollutants in actual runoff, and the standard methods and HACH kits were used to measure the concentrations of the pollutants in the samples (see Li, 2019 for detail). The four bioretention columns experienced a 'mature' period in Year 1, which made them function consistently (in terms of hydraulic performances) in Year 2 (Li, 2019).…”

“…Both bioretention columns demonstrated a high pollutant load reduction capability for phosphate, nitrite, and ammonium, but chloride and nitrate loads increased after the bioretention due to the leaching effect. During the winter experiments, influent with a high concentration of sodium chloride flowed into the soil columns (Li, 2019), which made the soil reach the saturation state of solute NaCl and salt precipitated. Chloride concentration was significantly larger in the outflow with 142% and 22% increase than that of inflow in the first summer week of Year 2 right after the winter season.…”

“…The second spring runoff event was a major melt of packed snow with a lower concentration of salts (see Table A1), an inflow rate of 14 mL/min, and a volume of water (39.3 mm) in 48 h (Li, 2019). The flow rate and volume were estimated based on the average yearly melted snow depth recorded in Edmonton (GoC, 2018; Li, 2019). During the fourth and fifth stages (Year 2 summer), five 1:2 year storm events were conducted, followed by one 1:5 storm event (37.3 mm precipitation) and one 1:10 year storm event (45.2 mm precipitation) (Li, 2019).…”

“…In this study, the initial values of $$$ {\theta}_r $$$, $$$ {\theta}_s $$$, α , and n were referred to Carsel and Parrish (1988) who summarized unsaturated hydraulic parameters for different soil classifications using van Genuchten (1980) model. The initial guess of K S was taken from Clapp and Hornberger (1978) whose average values of saturated conductivity were higher than Carsel and Parrish (1988)'s estimations, and the selection was based on the observation results in Li (2019) and Kratky (2019)'s experiments. Specifically, for the topsoil layer, the initial guesses of $$$ {\theta}_r $$$, $$$ {\theta}_s $$$, α , n , and K S of topsoil were all larger than those for the middle soil media layer because the compost added in topsoil increased effective friction angle, saturated hydraulic conductivity and water content (Duzgun et al, 2021).…”

“…Li (2019) and Kratky (2019) at the University of Alberta, Canada, conducted laboratory experiments of four bioretention columns and their data were used for the HYDRUS 1D modelling in this study (the experiments have been published as Li, Kratky, et al (2021) and Kratky et al (2021)). The columns were typical bioretention cells, which consisted of vegetation and mulch layer at the top, topsoil with organic matters as plant soil, middle soil media layer, gravel layer, and underdrain, as shown in Figure 1.…”