Urban stormwater bioretention reduces runoff and improves water quality: A global meta-analysis of field studies

Abstract

• Bioretention systems retained 63 % of inflow volumes and reduced peak flows by 74 %. • Load reduction was higher than concentration reduction due to volume retention. • Filter media sand content was positively correlated to peak flow reduction. • Smaller bioretention basins were better at reducing volumes than larger ones. • Lined systems did not reduce less volume than unlined ones, but were much smaller. Urbanisation adversely impacts waterway health, which can result in increased flow volumes, flow frequency and stormwater pollutant loads. Stormwater bioretention is a stormwater management tool that can reduce stormwater flow volumes and pollutants. Whilst these systems are constructed worldwide, we still have limited knowledge about how they behave in reality when installed in urban landscapes. As such, this investigation aimed to identify the stormwater retention and pollutant load reduction performance of stormwater bioretention systems monitored across the globe in urban areas and identify parameters that may influence the performance. We conducted a meta -analysis of stormwater retention performance and pollutant load and concentration reduction by field bioretention systems published in academic literature. Based on 50 assets, we found that in the urban landscape, bioretention systems can, on average, reduce stormwater runoff volume by 63 % (SD = 26 %) and reduce peak flows by 74 % (SD = 29 %). Additionally, bioretention systems were able to reduce total suspended solids load by an average of 80 % (SD = 21 %), total nitrogen loads by 55 % (SD = 25 %), and total phosphorus loads by 62 % (SD = 29 %). Lower performance was noted in terms of pollutant concentration reduction compared to load reduction. There were several critical findings in this study, such as smaller bioretention surface area had higher volumetric percent reduction which indicates good flow distribution, and field studies confirm the presence of saturated zone increases TN removal, as in lab studies. This investigation provides evidence that field-scale stormwater bioretention basins in urban landscapes can reduce stormwater volumes, peak flows, and improve stormwater quality.

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