Bioretention Technology: Overview of Current Practice and Future Needs

TLDR

Bioretention, including bioinfiltration and rain gardens, is a widely used storm‑water tool in urban watersheds, driven by low‑impact development goals and evolving maintenance practices that influence long‑term performance. The study highlights persistent design questions for bioretention, including optimal bowl depth, media depth and composition, underdrain configuration, pretreatment, and vegetation selection. Bioretention removes pollutants through filtration, adsorption, and possibly biological treatment, with load reductions arising from both concentration attenuation and runoff volume reduction that link water quality to hydrologic performance. Initial studies demonstrate that bioretention substantially reduces runoff volume and peak flows, and over the past decade has consistently produced low effluent loads for suspended solids, nutrients, hydrocarbons, heavy metals, and even pathogenic bacteria and thermal pollution. Bioretention usage will grow as design guidance matures as a result of continued research and application.

Abstract

Bioretention, or variations such as bioinfiltration and rain gardens, has become one of the most frequently used storm-water management tools in urbanized watersheds. Incorporating both filtration and infiltration, initial research into bioretention has shown that these facilities substantially reduce runoff volumes and peak flows. Low impact development, which has a goal of modifying postdevelopment hydrology to more closely mimic that of predevelopment, is a driver for the use of bioretention in many parts of the country. Research over the past decade has shown that bioretention effluent loads are low for suspended solids, nutrients, hydrocarbons, and heavy metals. Pollutant removal mechanisms include filtration, adsorption, and possibly biological treatment. Limited research suggests that bioretention can effectively manage other pollutants, such as pathogenic bacteria and thermal pollution, as well. Reductions in pollutant load result from the combination of concentration reduction and runoff volume attenuation, linking water quality and hydrologic performance. Nonetheless, many design questions persist for this practice, such as maximum pooling bowl depth, minimum fill media depth, fill media composition and configuration, underdrain configuration, pretreatment options, and vegetation selection. Moreover, the exact nature and impact of bioretention maintenance is still evolving, which will dictate long-term performance and life-cycle costs. Bioretention usage will grow as design guidance matures as a result of continued research and application.