Bioretention storm-water control measures help manage runoff from impervious surfaces to prevent environmental issues downstream. Researchers studied three sites and found that the key to bioretention performance is the Bioretention Abstraction Volume (BAV), which depends on the storage capacity of the soil and surface bowl. The BAV determines how much runoff can be stored, leading to predictable water volumetric performance. This study provides insights for designing effective bioretention systems.