27 - Bioretention Lessons Learned

This presentation offers key insights drawn from more than two decades of research into bioretention practices. Bioretention, encompassing both biofiltration and bioinfiltration, is a vital component of sustainable stormwater management. However, it is essential to recognize the nuanced differences between these practices and their distinct objectives. Biofiltration primarily aims to filter stormwater before it re-enters the runoff management system. Our research has revealed an often-overlooked issue: the release of significant quantities of phosphate, a major pollutant in receiving water bodies, from biofilters. This emphasizes the need for a deeper understanding of what transpires within the filter bed. On the other hand, bioinfiltration is designed to facilitate the infiltration of stormwater into the ground, which is an improvement over biofiltration. However, assumptions about the ground's ability to adsorb dissolved pollutants may not hold true in all cases, raising questions about the efficacy of this practice. In terms of assessing infiltration rates, our research suggests that synthetic runoff tests provide the most precise measurements, aligning closely with the desired outcome. Comparatively, infiltration point measurements, while valuable, introduce uncertainty due to their focus on saturated hydraulic conductivity, which must be translated into drainage time. Measuring infiltration rates post-runoff events, while an option, is less accurate and costlier than the aforementioned methods. Looking forward, there remains a significant research gap: the design of bioinfiltration facilities often lacks reliable data on infiltration rates, and the field requires the development of a methodology to ascertain whether bioinfiltration is a suitable design choice for specific locations.