Factors affecting the permeability of the growing media used in bioretention systems

Bioretention systems reduce rainfall runoff and improve runoff quality in "low impact development practices". However, existing studies have rarely focused on factors that affect the permeability of the media used in bioretention systems. Experiments were conducted to simulate runoff suspended solid (SS) load into bioretention systems. The media permeability performances of 10 types of bioretention systems were analyzed. The influence of different factors (media composition, media thickness, plants, influent load, and submerged area) on the permeability of the media in bioretention systems was discussed. The results show that the saturated permeability coefficients of the devices with SS influent finally maintained at 9.77-72.63% of the initial K values and reached the asymptotic values. Different design factors considerably influenced the permeability performance of bioretention systems. The proper composition of the materials in the media layer improves penetration performance, but attention also needs to be paid to its anti-clogging performance to maintain better permeability after construction. Although designs that reduce the thickness of the media layer have a high initial permeability coefficient and will improve initial permeability, they are not conducive to the maintenance of permeability after construction. Plants with thicker rhizomes and fewer fibrous roots are more conducive to maintaining the permeability of the facility. The increase in influent SS load has a more adverse effect on the permeability of the device compared to the increase in hydraulic load. Setting submerged zone reduces the initial permeability of the facility, the anti-clogging performance of the device, and is not conducive to the maintenance of permeability after the system has been constructed.