The terms “high-rate biofiltration” and “runoff reduction” aren’t often used in the same sentence. The engineering community has a preconceived notion that a high-rate biofilter with an underdrain (like Filterra®) can’t provide runoff reduction benefits because the stormwater it treats moves through the practice too quickly. However, with the proper design considerations, we can maximize the capability of a high-rate biofilter to provide appreciable runoff reduction. 

When it comes to using hydrodynamic separator (HDS) treatment devices, it is becoming commonplace to integrate them into storm sewer networks without worrying