Biofiltration systems usually consist of a swale or pond planted with dense semi aquatic vegetation. Rainwater collects in this area before percolating down through the biofiltration media. It will then be directed to drain away through pipes into waterways.
The primary feature of a biofiltration media is to meet specifications for hydraulic conductivity which enables the media to drain quickly in flash flood situations. It also requires a proportion of organic matter to house the necessary microbiology.